Staphylococcus aureus (S. aureus) infection is a serious threat to global health. This study aimed to investigate the anti-virulence efficacy of tigecycline against S. aureus. We used highly virulent S. aureus strains SA75 and JP30 to evaluate the effect of tigecycline on virulence, both of them isolated from the clinic. The MIC value of tigecycline against SA75 was 0.125 µg/mL, and that against JP30 was 0.25 µg/mL. Tigecycline did not affect the growth ability of bacteria at 0.015 µg/mL. Thus, subsequent discussions will focus on the effect of antibiotics at the latter subinhibitory concentrations that did not affect growth. First, the sub-MICs of tigecycline not only enhanced the sensitivity of S. aureus to oxidants and human whole blood but also weakened the hemolytic activity and cell adhesion level of S. aureus. Second, it undermined the survival of S. aureus in RAW264.7 and attenuated the macrophage inflammatory response induced by S. aureus. On the contrary, tigecycline decreased the hemolytic activity, as well as the skin abscess formation and bacterial burden in mice. Most importantly, it significantly decreased the expression of hla, hlgB, hlgC, spa, sbi, saeR, sak, tst, and coa genes by RT-qPCR and the protein expression of α-toxin. Altogether, the sub-MICs of tigecycline might be a promising agent to attenuate the virulence of S. aureus and its host immune response by inhibiting the SaeRS two-component system and the product of α-toxin.IMPORTANCEIn this study, the sub-MICs of tigecycline decreased the resistance of S. aureus to oxidants and human whole blood. Moreover, tigecycline weakened the cell adhesion level of S. aureus and skin abscess formation in mice by reducing bacterial burden. Remarkably, tigecycline decreased the hemolytic activity and significantly downregulated the expression of various virulence genes and α-toxin. This research highlighted that the sub-MICs of tigecycline might be a promising agent to attenuate the virulence of S. aureus by inhibiting the product of α-toxin.

SUMMARYStaphylococcus aureus is a major human pathogen. It can cause many types of infections, in particular bacteremia, which frequently leads to infective endocarditis, osteomyelitis, sepsis, and other debilitating diseases. The development of secondary infections is based on the bacterium's ability to associate with endothelial cells lining blood vessels. The success of endothelial colonization and infection by S. aureus relies on its ability to express a wide array of cell wall-anchored and secreted virulence factors. Establishment of endothelial infection by the pathogen is a multistep process involving adhesion, invasion, extravasation, and dissemination of the bacterium into surrounding tissues. The process is dependent on the type of endothelium in different organs (tissues) and pathogenetic potential of the individual strains. In this review, we report an update on the organization of the endothelium in the vessels, the structure and function of the virulence factors of S. aureus, and the several aspects of bacteria-endothelial cell interactions. After these sections, we will discuss recent advances in understanding the specific mechanisms of infections that develop in the heart, bone and joints, lung, and brain. Finally, we describe how neutrophils bind to endothelial cells, migrate to the site of infection to kill bacteria in the tissues, and how staphylococci counteract neutrophils' actions. Knowledge of the molecular details of S. aureus-endothelial cell interactions will promote the development of new therapeutic strategies and tools to combat this formidable pathogen.

This study reviews Staphylococcus aureus, a significant pathogen in both hospital and community-acquired infections, addressing its epidemiology, pathogenesis, and antimicrobial resistance. It highlights virulence mechanisms, such as adhesion factors, toxins, enzymes, and biofilms, which contribute to survival and immune evasion. The spread of resistance occurs through the transfer of mobile genetic elements like SCCmec and genetic mutations. The analysis also compares hospital and community strains, including multidrug-resistant lineages like MRSA, VISA, and VRSA. The study concludes that S. aureus presents a major public health challenge, requiring new therapeutic approaches and preventive strategies.

Panton-Valentine leukocidin (PVL) is a staphylococcal toxin associated with chronic/recurrent skin and soft tissue infections (SSTIs) and necrotizing pneumonia. Its detection in clinical isolates of Staphylococcus aureus warrants aggressive therapy and infection control measures. However, PVL detection relies on molecular methods of limited use, especially in outpatient or resource-poor settings. In order to aid the development of a lateral flow (LF) test for PVL, clinical isolates from SSTIs were collected in 2020/21 at three laboratories in two cities in the Eastern part of Germany. After the exclusion of duplicate and serial isolates, 83 isolates were eligible. These were tested using an experimental LF test for PVL production. They were also characterized using DNA microarrays, facilitating the detection of virulence and resistance markers as well as the assignment to clonal complexes and epidemic/pandemic strains. Thirty-nine isolates (47%) were PVL-positive, and the LF results were in 81 cases (97.6%) concordant with genotyping. One false-positive and one false-negative case were observed. This translated into a diagnostic sensitivity of 0.974 and a diagnostic specificity of 0.977. The most common PVL-positive MSSA lineages were CC152 (n = 6), CC121 (n = 4), and CC5 and CC30 (each n = 2). Thirty isolates (36%) were mecA-positive. The MRSA rate among PVL-negatives was 20% (nine isolates), but among the PVL-positives, it was as high as 54% (n = 21). The most common PVL-MRSA strains were CC398-MRSA-VT (n = 5), CC5-MRSA-IV "Sri Lanka Clone" (n = 4), CC8-MRSA-[mec IV+Hg] "Latin American USA300" (n = 4), and CC22-MRSA-IV (PVL+/tst+) (n = 2). While the PVL rate was similar just like the German isolates from a previous study a decade before, the MRSA rate among PVL-positives was clearly higher. All PVL-MRSA strains detected, as well as the most common methicillin-susceptible lineage (CC152), are known to be common locally in other parts of the world, and might, thus, be regarded as travel-associated. Therefore, patients with suspected PVL-associated disease should be asked for their history of travel or migration, and, in case of hospitalization, they should be treated as MRSA cases until proven otherwise.

Panton-Valentine leukocidin (PVL)-producing Staphylococcus aureus (S. aureus) is a rare but clinically significant cause of community-acquired pneumonia (CAP). This toxin leads to extensive tissue destruction and severe inflammation, often progressing to necrotizing pneumonia, septic shock, and multiorgan failure, representing a challenge in medical practice due to its rapid progression and poor prognosis. We discuss a case of a 65-year-old diabetic male who developed severe CAP leading to septic shock, respiratory failure, and multiorgan dysfunction. Despite initial empirical antibiotic therapy, the patient deteriorated and died within 24 hours of ICU admission. Blood and sputum cultures later revealed methicillin-sensitive S. aureus (MSSA) positive for PVL. This case highlights the challenge of early diagnoses, the importance of prompt recognition, and the role of targeted therapies in infection control, antibiotics, and intravenous immunoglobulin. Early identification of PVL in suspected cases of severe pneumonia can improve survival, especially if treated with appropriate antibiotics and immune modulators within the first 24-48 hours. Although it is not a common diagnosis, clinicians should be aware of this possibility, especially if dealing with severe refractory shock, even in immunocompetent individuals.

Pandemics from viral respiratory tract infections in the 20th and early 21st centuries were associated with high mortality, which was not always caused by a primary viral infection. It has been observed that severe course of infection, complications and mortality were often the result of co-infection with other pathogens, especially Staphylococcus aureus. During the COVID-19 pandemic, it was also noticed that patients infected with S. aureus had a significantly higher mortality rate (61.7%) compared to patients infected with SARS-CoV-2 alone. Our previous studies have shown that S. aureus strains isolated from patients with COVID-19 had a different protein profile than the strains in non-COVID-19 patients. Therefore, this study aims to analyze S. aureus strains isolated from COVID-19 patients in terms of their pathogenicity by analyzing their virulence genes, adhesion, cytotoxicity and penetration to the human pulmonary epithelial cell line A549. We have observed that half of the tested S. aureus strains isolated from patients with COVID-19 had a necrotizing effect on the A549 cells. The strains also showed greater variability in terms of their adhesion to the human cells than their non-COVID-19 counterparts.

Bacterial infections of the respiratory tract cause millions of deaths annually. Several diseases exist wherein (1) bacterial infection is the main cause of disease (e.g., tuberculosis and bacterial pneumonia), (2) bacterial infection is a consequence of disease and worsens the disease prognosis (e.g., cystic fibrosis), and (3) bacteria-triggered inflammation propagates the disease (e.g., chronic obstructive pulmonary disease). Current approaches to combat infections generally include long and aggressive antibiotic treatments, which challenge patient compliance, thereby making relapses common and contributing to the development of antibiotic resistance. Consequently, the proportion of infections that cannot be treated with conventional antibiotics is rapidly increasing, and novel therapies are urgently needed. In this context, antimicrobial peptides (AMPs) have received considerable attention as they may exhibit potent antimicrobial effects against antibiotic-resistant bacterial strains but with modest toxicity. In addition, some AMPs suppress inflammation and provide other host defense functions (motivating the alternative term host defense peptides (HDPs)). However, the delivery of AMPs is complicated because they are large, positively charged, and amphiphilic. As a result of this, AMP delivery systems have recently attracted attention. For airway infections, the currently investigated delivery approaches range from aerosols and dry powders to various self-assembly and nanoparticle carrier systems, as well as their combinations. In this paper, we discuss recent developments in the field, ranging from mechanistic mode-of-action studies to the application of these systems for combating bacterial infections in the airways.

This study aims to enhance understanding of necrotizing pneumonia and toxic shock syndrome by analyzing an adult case of community-acquired necrotizing pneumonia caused by co-infection of Influenza A (H1N1) and Staphylococcus aureus with LukS-PV and LukF-PV virulence factor genes.

The clinical data of one patient admitted to the intensive care unit (ICU) with co-infection of Influenza A (H1N1) and Staphylococcus aureus was retrospectively analyzed.

The patient exhibited typical clinical manifestations of viral and Staphylococcus aureus co-infection, including necrotizing pneumonia and toxic shock syndrome. The presence of LukS-PV and LukF-PV virulence factor genes of Staphylococcus aureus was detected in the patient's bronchoalveolar lavage fluid. Unfortunately，although antiviral agents (oseltamivir) and antibiotics (linezolid, imipenem-cilastatin) were timely administrated, as well as corticosteroids for anti-inflammatory purposes, the patient's condition was progressively deteriorated and eventually led to death.

Clinical practitioners should be vigilant about the co-infection of Influenza virus and Staphylococcus aureus, particularly when the latter carries virulence factors. The presence of virulence factor genes of Staphylococcus aureus can lead to necrotizing pneumonia with a poor prognosis. This is a particular concern because both infections can be life threatening in young adults.

Toxic shock syndrome (TSS) is a rare disease responsible for significant morbidity and mortality. Intravenous immunoglobulin (IG) therapy in paediatric TSS could improve shock and organ failure, but more consistent efficacy and safety data are needed. Our objective was to determine whether a randomised clinical trial (RCT) assessing intravenous IG in TSS in children is feasible.

We performed a multicentre, feasibility, double-blind RCT assessing efficacy of high-dose intravenous IG versus albumin 4% (control group) within the first 12 hours of shock onset. Included patients were aged above 1 month and below 18 years with suspected TSS and septic shock. Feasibility was assessed by measuring inclusion rate, protocol compliance and missing data regarding death and the Pediatric Logistic Organ Dysfunction-2 (PELOD-2) Score. Other secondary clinical outcomes were evaluated during hospital stay, at 60 day and 1 year.

28 patients, admitted in 6 paediatric intensive care units during 36 consecutive months and followed for 1 year, received the allocated treatment: 13 in intravenous IG group, 15 in control group. The median age was 10.6 years and the sex ratio was 1. Inclusion rate was above 50%, protocol deviations were below 30% and missing data regarding death and PELOD-2 Score below 10%. No difference concerning secondary clinical outcomes between groups was observed, and more adverse events were reported in the control group.

It seems to be feasible to conduct an RCT assessing intravenous IG efficacy and safety in paediatric TSS but must be realised internationally, with choice of a clinically relevant endpoint and a specific design in order to be realistic.

NCT02219165.

How to cite this article: Khilnani GC, Tiwari P, Mittal S, Kulkarni AP, Chaudhry D, Zirpe KG, et al. Guidelines for Antibiotics Prescription in Critically Ill Patients. Indian J Crit Care Med 2024;28(S2):S104-S216.

A previously healthy woman, 5 weeks pregnant, was admitted to the intensive care unit in critical condition for septic shock and acute respiratory distress syndrome due to methicillin-resistant Staphylococcus aureus (MRSA) after being infected with Influenza for 3 days. The patient in this case suffered from severe sequelae due to necrotizing pneumonia and later died on the 20th day after admission. We would like to remind clinicians to be aware of this rare but serious diagnosis. The key is to begin appropriate treatment immediately because MRSA necrotizing pneumonia is mediated by toxins and once the toxins are released they cannot be limited by antibiotic treatments. Necrotizing pneumonia related to MRSA should be considered in young patients with pneumonia, sepsis, and neutropenia following seasonal influenza infection with rapidly progressive symptoms.

We present a case report of diffuse alveolar hemorrhage (DAH), which presented with massive hemoptysis and impending airway compromise. A previously healthy 33-year-old female presented to the emergency department with dyspnea, chest pain, and massive hemoptysis. Due to impending respiratory failure, the patient was placed on mechanical ventilation and a bronchoscopy revealed a diagnosis of DAH. Throughout the hospital course, the patient received antibiotics, steroids, fresh frozen plasma (FFP), cryoprecipitate, tranexamic acid (TXA), and multiple blood transfusions. The patient was subsequently placed on extracorporeal membrane oxygenation (ECMO), but despite these life-saving measures, the patient died less than 48 hours after her initial presentation. This case serves as a harrowing reminder of DAH's destructive capabilities and the importance of rapid, aggressive management.

Staphylococcus aureus bacteremia continues to be associated with significant morbidity and mortality, despite improvements in diagnostics and management. Persistent infections pose a major challenge to clinicians and have been consistently shown to increase the risk of mortality and other infectious complications. S. aureus, while typically not considered an intracellular pathogen, has been proven to utilize an intracellular niche, through several phenotypes including small colony variants, as a means for survival that has been linked to chronic, persistent, and recurrent infections. This intracellular persistence allows for protection from the host immune system and leads to reduced antibiotic efficacy through a variety of mechanisms. These include antimicrobial resistance, tolerance, and/or persistence in S. aureus that contribute to persistent bacteremia. This review will discuss the challenges associated with treating these complicated infections and the various methods that S. aureus uses to persist within the intracellular space.

Staphylococcus aureus is one of the primary pathogenic agents found in cheeses produced with raw milk. Some strains of S. aureus are enterotoxigenic, possessing the ability to produce toxins responsible for staphylococcal food poisoning when present in contaminated foods. This study aimed to genotypically characterize, assess the antimicrobial resistance profile, and examine the enterotoxigenic potential of strains of S. aureus isolated from artisanal colonial cheese. Additionally, a bacterial diversity assessment in the cheeses was conducted by sequencing the 16S rRNA gene. The metataxomic profile revealed the presence of 68 distinct species in the cheese samples. Fifty-seven isolates of S. aureus were identified, with highlighted resistance to penicillin in 33% of the isolates, followed by clindamycin (28%), erythromycin (26%), and tetracycline (23%). The evaluated strains also exhibited inducible resistance to clindamycin, with nine isolates considered multidrug-resistant (MDR). The agr type I was the most prevalent (62%) among the isolates, followed by agr type II (24%). Additionally, ten spa types were identified. Although no enterotoxins and their associated genes were detected in the samples and isolates, respectively, the Panton-Valentine leukocidin gene (lukS-lukF) was found in 39% of the isolates. The presence of MDR pathogens in the artisanal raw milk cheese production chain underscores the need for quality management to prevent the contamination and dissemination of S. aureus strains.

Staphylococcus aureus (S. aureus) is an important pathogen in both community-acquired and hospital-acquired pneumonia. S. aureus pneumonia has a high mortality rate and serious complications. Resistance to multiple antibiotics is a major challenge in the treatment of S. aureus pneumonia. Understanding the antibiotic resistance profile of S. aureus and the risk factors for mortality can help optimize antibiotic regimens and improve patient outcomes in S. aureus pneumonia.

A prospective cohort study of 118 patients diagnosed with S. aureus pneumonia between May 2021 and June 2023 was conducted, with a 30-day follow-up period. Demographic information, comorbidities, Charlson Comorbidity Index, clinical characteristics, outcomes, and complications were collected for each enrolled case. The data were processed and analyzed using R version 3.6.2.

S. aureus pneumonia has a 30-day mortality rate of approximately 50%, with complication rates of 22% for acute respiratory distress syndrome (ARDS), 26.3% for septic shock, and 14.4% for acute kidney injury (AKI). Among patients with methicillin-resistant S. aureus (MRSA) pneumonia treated with vancomycin (n = 40), those with a vancomycin minimum inhibitory concentration (MIC) ≤ 1 had significantly higher cumulative survival at day 30 compared to those with MIC ≥ 2 (log-rank test p = 0.04). The prevalence of MRSA among S. aureus isolates was 84.7%. Hemoptysis, methicillin resistance, acidosis (pH < 7.35), and meeting the Infectious Diseases Society of America/American Thoracic Society (IDSA/ATS) criteria for severe pneumonia were significantly associated with mortality in a multivariate Cox regression model based on the adaptive least absolute shrinkage and selection operator (LASSO).

S. aureus pneumonia is a severe clinical condition with high mortality and complication rates. MRSA has a high prevalence in Can Tho City, Vietnam. Hemoptysis, methicillin resistance, acidosis (pH < 7.35), and meeting the IDSA/ATS criteria for severe pneumonia are risk factors for mortality in S. aureus pneumonia.

Persistent nasal carriage has been associated with Staphylococcus aureus infection. Previous S. aureus studies in Asia have primarily focused on clinical patients, providing limited information on persistent nasal carriage among the general adult population.

This study examined 143 healthy adults in a community in Jiangsu, China. Nasal swab samples were collected 10 times. The colonization status was identified using SPA typing. We also determined antimicrobial susceptibility, genotype, and genomic characteristics of S. aureus.

The prevalence of S. aureus nasal carriage among the community individuals was on average 16.78%. The carriage rates of methicillin-resistant S. aureus and multidrug-resistant S. aureus were 6.29% and 7.69%, respectively. We identified 8.39% persistent carriers, 39.16% intermittent carriers, and 52.45% noncarriers. Furthermore, family members displayed concordance in terms of genotype and genomic characteristics.

Persistent nasal sampling captured intermittent carriers that were missed during short-term sampling, thus highlighting the necessity for regular community testing. SPA typing can serve as a rapid method for determining S. aureus colonization. The potential for intrafamilial transmission of S. aureus is evident, with persistent carriers being the most probable source of infection.

Staphylococcus aureus is a Gram-positive bacterium and one of the most prevalent infectious disease-related causes of morbidity and mortality in adults. This pathogen can trigger a broad spectrum of diseases, from sepsis and pneumonia to severe skin infections that can be fatal. In this review, we will provide an overview of S. aureus and discuss the extensive literature on epidemiology, transmission, genetic diversity, evolution and antibiotic resistance strains, particularly methicillin resistant S. aureus (MRSA). While many different virulence factors that S. aureus produces have been investigated as therapeutic targets, this review examines recent nanotechnology approaches, which employ materials with atomic or molecular dimensions and are being used to diagnose, treat, or eliminate the activity of S. aureus. Finally, having a deeper understanding and clearer grasp of the roles and contributions of S. aureus determinants, antibiotic resistance, and nanotechnology will aid us in developing anti-virulence strategies to combat the growing scarcity of effective antibiotics against S. aureus.

A 22-year-old Vietnamese man was referred to our hospital owing to cough, dyspnea, and difficulty moving. The patient was diagnosed with community-acquired Panton-Valentine leukocidin-positive methicillin-resistant Staphylococcus aureus (MRSA) bacteremia and necrotizing pneumonia. Treatment involved vancomycin (VCM) and meropenem, and the MRSA bacteremia improved. However, lung tissue destruction progressed. Therefore, linezolid was added to the VCM regimen, and this intervention led to the patient's recovery, and he was discharged from the hospital. Here, we report a case in which the patient was treated with a combination of two anti-MRSA drugs and was cured.

Staphylococcus aureus (S. aureus) is a prominent pathogen responsible for both hospital-acquired and community-acquired infections. Among its arsenal of virulence factors, Panton-Valentine Leucocidin (PVL) is closely associated with severe diseases such as profound skin infections and necrotizing pneumonia. Patients infected with pvl-positive S. aureus often exhibit more severe symptoms and carry a substantially higher mortality risk. Therefore, it is crucial to promptly and accurately detect pvl-positive S. aureus before initiating protective measures and providing effective antibacterial treatment.

In this study, we propose a precise identification and highly sensitive detection method for pvl-positive S. aureus based on recombinase-assisted amplification and the CRISPR-ERASE strip which we previously developed.

The results revealed that this method achieved a detection limit of 1 copy/μL for pvl-positive plasmids within 1 hour. The method successfully identified all 25 pvl-positive and 51 pvl-negative strains among the tested 76 isolated S. aureus samples, demonstrating its concordance with qPCR.

These results show that the CRISPR-ERASE detection method for pvl-positive S. aureus has the advantages of high sensitivity and specificity, this method combines the characteristics of recombinase-assisted amplification at room temperature and the advantages of ERASE test strip visualization, which can greatly reduce the dependence on professional laboratories. It is more suitable for on-site detection than PCR and qPCR, thereby providing important value for rapid on-site detection of pvl.

Acute respiratory distress syndrome (ARDS) is one of the major problems in COVID-19 that is not well understood. ARDS is usually complicated by co-infections in hospitals. Although ARDS is inherited by Europeans and Africans, this is not clear for those from the Middle East. There are severe limitations in correlations made between COVID-19, ARDS, co-infectome, and patient demographics. We investigated 298 patients for associations of ARDS, coinfections, and patient demographics on COVID-19 patients' outcomes. Of the 149 patients examined for ARDS during COVID-19, 16 had an incidence with a higher case fatality rate (CFR) of 75.0% compared to those without ARDS (27.0%) (p value = 0.0001). The co-infectome association showed a CFR of 31.3% in co-infected patients; meanwhile, only 4.8% of those without co-infections (p value = 0.01) died. The major bacteria were Acinetobacter baumannii and Escherichia coli, either alone or in a mixed infection with Klebsiella pneumoniae. Kaplan-Meier survival analysis of COVID-19 patients with and without ARDS revealed a significant difference in the survival time of patients with ARDS (58.8 +/- 2.7 days) and without ARDS (41.9 +/- 1.8 days) (p value = 0.0002). These findings prove that increased hospital time was risky for co-infectome-induced SDRS later on. This also explained that while empiric therapy and lethal ventilations delayed the mortality in 75% of patients, they potentially did not help those without co-infection or ARDS who stayed for shorter times. In addition, the age of patients (n = 298) was significantly associated with ARDS (72.9 +/- 8.9) compared to those without it (56.2 +/- 15.1) and was irrespective of gender. However, there were no significant differences neither in the age of admitted patients before COVID-19 (58.5 +/- 15.3) and during COVID-19 (57.2 +/- 15.5) nor in the gender and COVID-19 fatality (p value 0.546). Thus, Gram-negative co-infectome potentially induced fatal ARDS, aggravating the COVID-19 outcome. These findings are important for the specific differential diagnosis of patients with and without ARDS and co-infections. Future vertical investigations on mechanisms of Gram-negative-induced ARDS are imperative since hypervirulent strains are rapidly circulating. This study was limited as it was a single-center study confined to Ha'il hospitals; a large-scale investigation in major national hospitals would gain more insights.

Staphylococcus aureus stands as one of the most pervasive pathogens given its morbidity and mortality worldwide due to its roles as an infectious agent that causes a wide variety of diseases ranging from moderately severe skin infections to fatal pneumonia and sepsis. S. aureus produces a variety of exotoxins that serve as important virulence factors in S. aureus-related infectious diseases and food poisoning in both humans and animals. For example, staphylococcal enterotoxins (SEs) produced by S. aureus induce staphylococcal foodborne poisoning; toxic shock syndrome toxin-1 (TSST-1), as a typical superantigen, induces toxic shock syndrome; hemolysins induce cell damage in erythrocytes and leukocytes; and exfoliative toxin induces staphylococcal skin scalded syndrome. Recently, Panton-Valentine leucocidin, a cytotoxin produced by community-associated methicillin-resistant S. aureus (CA-MRSA), has been reported, and new types of SEs and staphylococcal enterotoxin-like toxins (SEls) were discovered and reported successively. This review addresses the progress of and novel insights into the molecular structure, biological activities, and pathogenicity of both the classic and the newly identified exotoxins produced by S. aureus.

Methicillin-resistant Staphylococcus aureus (MRSA) is a leading cause of severe and often fatal infections. MRSA epidemics have occurred in waves, whereby a previously successful lineage has been replaced by a more fit and better adapted lineage. Selection pressures in both hospital and community settings are not uniform across the globe, which has resulted in geographically distinct epidemiology. This review focuses on the mechanisms that trigger the establishment and maintenance of current, dominant MRSA lineages across the globe. While the important role of antibiotic resistance will be mentioned throughout, factors which influence the capacity of S. aureus to colonize and cause disease within a host will be the primary focus of this review. We show that while MRSA possesses a diverse arsenal of toxins including alpha-toxin, the success of a lineage involves more than just producing toxins that damage the host. Success is often attributed to the acquisition or loss of genetic elements involved in colonization and niche adaptation such as the arginine catabolic mobile element, as well as the activity of regulatory systems, and shift metabolism accordingly (e.g., the accessory genome regulator, agr). Understanding exactly how specific MRSA clones cause prolonged epidemics may reveal targets for therapies, whereby both core (e.g., the alpha toxin) and acquired virulence factors (e.g., the Panton-Valentine leukocidin) may be nullified using anti-virulence strategies.

USA300 is an MRSA clone producing PVL, a toxin associated with SSTIs. ΨUSA300 is a USA300 variant recently identified in Japan by Takadama et al. (15). Here, we found that the prevalence rate of PVL-positive MRSA in S. aureus was elevated in the Japanese community, and ΨUSA300 accounted for most of them. ΨUSA300 strains have been isolated from several areas in Japan and were associated with deep-seated SSTIs. This study highlighted the emerging threat posed by ΨUSA300 in Japan.

This study aimed to investigate the presence of mecA and pvl genes in coagulase negative Staphylococcus (CNS) species isolated from bovine mastitis in smallholder dairy farms by using PCR. A total of 602 mammary quarter milk samples belong to 170 cows with mastitis were used. Identification of species was achieved by using the commercial Gram-positive identification kit and a total of 52 (8.6%) CNS species were isolated. The most frequently isolated species was Staphylococcus capitis (n = 15, 28.8%), followed by Staphylococcus saccharolyticus (n = 12, 23.1%), Staphylococcus simulans (n = 8, 15.4%), Staphylococcus haemolyticus (n = 5, 9.6%), Staphylococcus cohnii (n = 4, 7.7%), Staphylococcus lentus (n = 4, 7.7%), Staphylococcus epidermidis (n = 2, 3.8%) and Staphylococcus saprophyticus (n = 2, 3.8%). The mecA gene positivity was found in the 13 (25%) of strains. Of the strains carrying mecA gene, eight also harbored the pvl gene. A total of pvl gene positivity was found as 30.8% (n = 16) in 52 CNS species. In conclusion, the present study showed that CNS isolated from cows with mastitis may be reservoir of mecA and pvl genes. To our knowledge, this is the first study showing the presence of mecA and pvl genes in CNS species isolated from bovine with mastitis in the smallholder dairy farms in Turkey.

To investigate the characteristics of Methicillin-Resistant Staphylococcus aureus (MRSA) in bone and joint infection (BJI) among children.

A total of 338 patients diagnosed with BJI from 2013 to 2022 in Children's Hospital of Fudan University were enrolled. Demographic information, microbiology culture results and laboratory findings, including white blood counts (WBC), C-reactive protein (CRP), procalcitonin (PCT), interleukin-6 (IL-6), and erythrocyte sedimentation rate (ESR) were collected and analyzed. MRSA was confirmed by antimicrobial susceptibility testing. Other MRSA-caused infections were randomly selected for comparison. Twenty-three virulence and antimicrobial resistance (AMR) genes were screened for MRSA strains. Multilocus sequence typing (MLST) and Staphylococcal protein A (spa) typing were performed using PCR amplification and sequencing.

Of the identified pathogens in BJI, MRSA accounted for 21.0% (47/224). Patients with BJI had high levels of initial CRP, white blood cell count (WBC) and IL-6. ST59 (43.9%) and t437 (37.6%) were the main MRSA subtypes isolated from the children. The major genotypes in BJI were ST59-t437 (29.8%) and ST22-t309 (14.9%), with high carriage of hemolysins including hla (94.4-100%), hlb (66.2-93.3%), and hld (100%). Notably, Panton-Valentine leukocidin (pvl) had a high prevalence (53.3%) in ST22-t309-MRSA. Other virulence genes including tst, seg and sei were more commonly detected in ST22-t309-MRSA (40.0-46.7%) than in ST59-t437-MRSA (4.2-9.9%). High-carriage AMR genes in MRSA included aph(3')/III (66.7-80%), ermB (57.5-73.3%) and ermC (66.7-78.9%). MRSA presented high-resistance to erythromycin (52.0-100%) and clindamycin (48.0-92.5%), different genotypes displayed variation in their susceptibilities to antibiotics.

The major MRSA genotype in BJI was ST59-t437, followed by ST22-t309, with a higher prevalence of the pvl gene. Continuous surveillance of pvl-positive ST22-t309-MRSA in pediatric BJI infections is thus required.

Staphylococcus aureus is a common cause of hospital-acquired pneumonia associated with high mortality. Adequate clinical treatment is impeded by increasing occurrence of antibiotic resistances. Understanding the underlying mechanisms of its virulence during infections is a prerequisite to finding alternative treatments. Here, we demonstrated that an increased nuclease activity of a S. aureus isolate from a person with cystic fibrosis confers a growth advantage in a model of acute lung infection compared to the isogenic strain with low nuclease activity. Comparing these CF-isolates with a common MRSA-USA300 strain with similarly high nuclease activity but significantly elevated levels of Staphylococcal Protein A (SpA) revealed that infection with USA300 resulted in a significantly increased bacterial burden in a model of murine lung infection. Replenishment with the cell wall-bound SpA of S. aureus, which can also be secreted into the environment and binds to tumor necrosis factor receptor -1 (TNFR-1) to the CF-isolates abrogated these differences. In vitro experiments confirmed significant differences in spa-expression between USA300 compared to CF-isolates, thereby influencing TNFR-1 shedding, L-selectin shedding, and production of reactive oxygen species through activation of ADAM17.

Background Panton-Valentine leukocidin (PVL) is one of the most important determinants of virulence in Staphylococcus aureus. It is associated with a propensity for complicating skin and soft tissue infections and necrotizing pneumonia. This study aims to quantitively examine the effect of ascorbic acid and nicotinamide on PVL production in the reference strain USA300. Methodology Sandwich enzyme-linked immunosorbent assay (ELISA) was used to quantitively measure the production of PVL via the commercial LukS sandwich ELISA kit (IBT Bio-services, MD, USA). Results Incubating USA300 with subinhibitory concentrations of antioxidants resulted in a statistically significant eight-fold reduction in PVL production at 1.25 mg/mL and 30 mg/mL for ascorbic acid and nicotinamide, respectively. Although the mechanism by which antioxidants inhibit PVL production is yet to be elucidated, we suggest that it can be due to interrupting PVL gene expression. Conclusions Ascorbic acid and nicotinamide have the potential to be toxin-suppressing agents that may be effective in supporting the bactericidal effect of antibiotics to improve the outcome of PVL-associated infections; however, further extensive research is required.

Staphylococcus aureus gamma-hemolysin CB (HlgCB) is a core-genome-encoded pore-forming toxin that targets the C5a receptor, similar to the phage-encoded Panton-Valentine leucocidin (PVL). Absolute quantification by mass spectrometry of HlgCB in 39 community-acquired pneumonia (CAP) isolates showed considerable variations in the HlgC and HlgB yields between isolates. Moreover, although HlgC and HlgB are encoded on a single operon, their levels were dissociated in 10% of the clinical strains studied. To decipher the molecular basis for the variation in hlgCB expression and protein production among strains, different regulation levels were analyzed in representative clinical isolates and reference strains. Both the HlgCB level and the HlgC/HlgB ratio were found to depend on hlgC promoter activity and mRNA processing and translation. Strikingly, only one single nucleotide polymorphism (SNP) in the 5' untranslated region (UTR) of hlgCB mRNA strongly impaired hlgC translation in the USA300 strain, leading to a strong decrease in the level of HlgC but not in HlgB. Finally, we found that high levels of HlgCB synthesis led to mortality in a rabbit model of pneumonia, correlated with the implication of the role of HlgCB in severe S. aureus CAP. Taken together, this work illustrates the complexity of virulence factor expression in clinical strains and demonstrates a butterfly effect where subtle genomic variations have a major impact on phenotype and virulence. IMPORTANCE S. aureus virulence in pneumonia results in its ability to produce several virulence factors, including the leucocidin PVL. Here, we demonstrate that HlgCB, another leucocidin, which targets the same receptors as PVL, highly contributes to S. aureus virulence in pvl-negative strains. In addition, considerable variations in HlgCB quantities are observed among clinical isolates from patients with CAP. Biomolecular analyses have revealed that a few SNPs in the promoter sequences and only one SNP in the 5' UTR of hlgCB mRNA induce the differential expression of hlgCB, drastically impacting hlgC mRNA translation. This work illustrates the subtlety of regulatory mechanisms in bacteria, especially the sometimes major effects on phenotypes of single nucleotide variation in noncoding regions.

The aim of this study was to determine the prevalence and characterization of Staphylococcus aureus isolated from 145 shrimp samples from 39 cities in China. The results show that 41 samples (28%) from 24 cities were positive, and most of the positive samples (39/41, 95.1%) were less than 110 MPN/g. Antimicrobial susceptibility testing showed that only seven isolates were susceptible to all 24 antibiotics, whereas 65.1% were multidrug-resistant. Antibiotic resistance genes that confer resistance to β-lactams, aminoglycosides, tetracycline, macrolides, lincosamides and streptogramin B (MLSB), trimethoprim, fosfomycin and streptothricin antibiotics were detected. All S. aureus isolates had the ability to produce biofilm and harbored most of the biofilm-related genes. Genes encoding one or more of the important virulence factors staphylococcal enterotoxins (sea, seb and sec), toxic shock syndrome toxin 1 (tsst-1) and Panton-Valentine leukocidin (PVL) were detected in 47.6% (30/63) of the S. aureus isolates. Molecular typing showed that ST15-t085 (27.0%, 17/63), ST1-t127 (14.3%, 9/63) and ST188-t189 (11.1%, 7/63) were the dominant genetic types. The finding of this study provides the first comprehensive surveillance on the incidence of S. aureus in raw shrimp in China. Some retained genotypes found in this food have been linked to human infections around the world.

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the major causes of a variety of infections in hospitals and the community. Their spread poses a serious public health problem worldwide. Nevertheless, in Tunisia and other African countries, very little molecular typing data on MRSA strains is currently available. In our study, a total of 64 MRSA isolates were isolated from clinical samples collected from burned patients hospitalized in the Traumatology and Burns Center of Ben Arous in Tunisia. The identification of the collection was based on conventional methods (phenotypic and molecular characterization). The characterization of the genetic support for methicillin resistance was performed by amplification of the mecA gene by polymerase chain reaction (PCR), which revealed that 78.12% of S. aureus harbors the gene. The resistance of all the collection to different antibiotic families was studied. Indeed, the analysis of strain antibiotic susceptibility confirmed their multi-resistant phenotype, with high resistance to ciprofloxacin, gentamicin, penicillin, erythromycin, and tetracycline. The resistance to the last three antibiotics was conferred by the blaZ gene (73.43%), the erm(C) gene (1.56%), the msr(A) gene (6.25%), and tet(M) gene (7.81%), respectively. The clonal diversity of these strains was studied by molecular typing of the accessory gene regulator (agr) system, characterization of the SCCmec type, and spa-typing. The results revealed the prevalence of agr types II and III groups, the SCCmec type III and II cassettes, and the dominance of spa type t233. The characterization of the eight enterotoxins genes, the Panton-Valentine leukocidin and the toxic shock syndrome toxin, was determined by PCR. The percentage of virulence genes detected was for enterotoxins (55%), tst (71.88%), leukocidin E/D (79.69%), and pvl (1.56%) factors. Furthermore, our results revealed that the majority of the strains harbor IEC complex genes (94%) with different types. Our findings highlighted the emergence of MRSA strains with a wide variety of toxins, leukocidin associated with resistance genes, and specific genetic determinants, which could constitute a risk of their spread in hospitals and the environment and complicate infection treatment.

Methicillin-resistant Staphylococcus aureus (MRSA) are spreading worldwide in hospital and community settings, thus posing a serious public health problem. Panton-Valentine Leukocidin (PVL), an important virulence factor of S. aureus, is a marker of community-acquired MRSA. Here we determined the prevalence of pvl genes among S. aureus isolates from different hospitals in the Gaza Strip, Palestine. A total of 285 S. aureus isolates were collected from five different hospitals in the Gaza Strip. All isolates were characterized for their susceptibility patterns to available antimicrobial agents and by using multiplex PCR for the detection of mecA and pvl genes. The overall prevalence of MRSA in Gaza hospitals was 70.2% (range: 76.3% to 65.5%) and that of pvl among S. aureus isolates was 29.8% (range: 32.9% to 26.2%). The pvl gene was equally prevalent among MRSA isolates (30.5%) and MSSA isolates (28.2%). The most effective antibiotics were rifampicin, vancomycin, and clindamycin, with susceptibility rates of 91.2%, 88.7%, and 84.6%, respectively. The highest percentage of strains were observed to be resistant to penicillin and amoxicillin with clavulanic acid-96.1% and 73.6%, respectively. Our results showed a high prevalence of MRSA and pvl-positive isolates in Gaza Strip hospitals, which likely reflects the situation in the community. It is mandatory to implement systematic surveillance of both hospital and community isolates, together with interventions (such as increased hand hygiene, use of hydroalcoholic solutions, and isolation of carriers) to limit their spread.

Background and Objectives: The purpose of this study was to assess the cytotoxicity and antibacterial effects of AgNP-impregnated Tetracalcium phosphate-dicalcium phosphate dihydrate (TTCP-DCPD). Materials and Methods: Using in vitro experiments, the cytotoxicity of AgNP-impregnated TTCP-DCPD against fibroblasts and osteocytes was assessed in terms of cell viability by water-soluble tetrazolium salt assay. To assess antibacterial effects, a disc diffusion test was used; osteomyelitis was induced first in vivo, by injection of methicillin-resistant Staphylococcus aureus into the tibia of rats. AgNP-impregnated TTCP-DCPD bone cement was then applied at various silver concentrations for 3 or 12 weeks. Antibacterial effects were assessed by culturing and reverse transcription-polymerase chain reaction (RT-PCR). For histological observation, the bone tissues were stained using hematoxylin and eosin. Results: Cell viability was decreased by the impregnated bone cement but did not differ according to AgNP concentration. The diameter of the growth-inhibited zone of MRSA was between 4.1 and 13.3 mm on the disks treated with AgNP, indicating antimicrobial effects. In vivo, the numbers of bacterial colonies were reduced in the 12-week treatment groups compared to the 3-week treatment groups. The groups treated with a higher (10×) dose of AgNP (G2-G5) showed a tendency of lower bacterial colony counts compared to the group without AgNP (G1). The PCR analysis results showed a tendency of decreased bacterial gene expression in the AgNP-impregnated TTCP-DCPD groups (G2-G5) compared to the group without AgNP (G1) at 3 and 12 weeks. In the H&E staining, the degree of inflammation and necrosis of the AgNP-impregnated TTCP-DCPD groups (G2-G5) showed a tendency to be lower at 3 and 12 weeks compared to the control group. Our results suggest that AgNP-impregnated TTCP-DCPD cement has antimicrobial effects. Conclusions: This study indicates that AgNP-impregnated TTCP-DCPD bone cement could be considered to treat osteomyelitis.

The bacterial pathogen Staphylococcus aureus harbors numerous virulence factors that impact infection severity. Beyond virulence gene presence or absence, the expression level of virulence proteins is known to vary across S. aureus lineages and isolates. However, the impact of expression level on severity is poorly understood due to the lack of high-throughput quantification methods of virulence proteins.

We present a targeted proteomic approach able to monitor 42 staphylococcal proteins in a single experiment. Using this approach, we compared the quantitative virulomes of 136 S. aureus isolates from a nationwide cohort of French patients with severe community-acquired staphylococcal pneumonia, all requiring intensive care. We used multivariable regression models adjusted for patient baseline health (Charlson comorbidity score) to identify the virulence factors whose in vitro expression level predicted pneumonia severity markers, namely leukopenia and hemoptysis, as well as patient survival.

We found that leukopenia was predicted by higher expression of HlgB, Nuc, and Tsst-1 and lower expression of BlaI and HlgC, while hemoptysis was predicted by higher expression of BlaZ and HlgB and lower expression of HlgC. Strikingly, mortality was independently predicted in a dose-dependent fashion by a single phage-encoded virulence factor, the Panton-Valentine leucocidin (PVL), both in logistic (OR 1.28; 95%CI[1.02;1.60]) and survival (HR 1.15; 95%CI[1.02;1.30]) regression models.

These findings demonstrate that the in vitro expression level of virulence factors can be correlated with infection severity using targeted proteomics, a method that may be adapted to other bacterial pathogens.

Introduction. Panton-Valentine leucocidin (PVL) toxin is a potential determinant of virulence associated with S. aureus infection.Gap Statement. The contribution of PVL to S. aureus pathogenicity remains unclear.Aim. To compare clinical outcomes in hospitalized patients with PVL-positive and PVL-negative community-acquired (CA) S. aureus bacteraemia.Methods. Three national datasets were combined to provide clinical and mortality data for patients with CA S. aureus blood culture isolates sent to the UK reference laboratory for PVL testing, August 2018 to August 2021. Multivariable logistic regression models were built for the effect of PVL positivity on 30 day all-cause mortality and 90 day readmission.Results. In 2191 cases of CA S. aureus bacteraemia, there was no association between PVL and mortality (adjusted odds ratio, aOR: 0·90, 95 % confidence interval, CI: 0·50-1·35, P=0·602) and no difference in median LOS (14 versus 15 days, P=0.169). PVL-positive cases had lower odds of readmission (aOR 0·74, CI 0·55-0.98, P=0·038). There was no evidence that MRSA status modified this effect (P=0·207).Conclusions. In patients with CA S. aureus bacteraemia PVL toxin detection was not associated with worse outcomes.