Staphylococcal Cassette Chromosome mec (SCCmec) Analysis of MRSA

Evaluation of a nucleic acid amplification system, GENECUBE, for rapid detection of staphylococcal nuc and mecA in blood culture samples

OBJECTIVE

This study determined whether the GENECUBE rapid nucleic acid amplification test could directly detect nuc and mecA genes in clinical blood culture samples of Staphylococcus and various other pathogens.

METHODS

Between September 2020 and December 2021, 537 blood culture samples from 192 patients with suspected bacteremia were tested using conventional assays (MicroScan WalkAway96 or VITEK 2 systems) and GENECUBE nuc and mecA assays. Isolates from samples with discrepant results between the conventional and GENECUBE assays were further evaluated using MALDI-TOF mass spectrometry, disk diffusion testing using cefoxitin, broth microdilution testing using oxacillin, and sequencing for mecA. Bacterial solutions containing a mixture of methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant Staphylococcus epidermidis (MRSE) were prepared to evaluate the limit of detection (LOD) of mecA.

RESULTS

Using conventional assays as the reference, the sensitivity, specificity, and positive and negative predictive values (95 % confidence interval) of GENECUBE were 100 % (96.8-100 %), 100 % (99.1-100 %), 100 % (96.8-100 %), and 100 % (99.1-100 %), respectively, for nuc detection and 100 % (96.1-100 %), 98.9 % (97.4-99.6 %), 94.9 % (88.5-98.3 %), and 100 % (99.2-100 %), respectively, for mecA detection. Sequencing analysis of five samples identified as methicillin-sensitive staphylococci using conventional assays and methicillin-resistant staphylococci using GENECUBE revealed the presence of methicillin-resistant isolates in all samples. The estimated LOD of mecA was 104 colony-forming units (CFU)/mL of MRSE with GENECUBE, compared with 105 CFU/mL with conventional assays.

CONCLUSION

The GENECUBE assay accurately detected mecA in positive blood culture samples and had higher sensitivity than conventional assays.

Tandem mobilization of anti-phage defenses alongside SCCmec elements in staphylococci

Recent research has identified multiple immune systems that bacteria use to protect themselves from viral infections. However, little is known about the mechanisms by which these systems horizontally spread, especially among bacterial pathogens. Here, we investigate antiviral defenses in staphylococci, opportunistic pathogens that constitute leading causes of antibiotic-resistant infections. We show that these organisms harbor a variety of anti-phage defenses encoded within or near SCC (staphylococcal cassette chromosome) mec cassettes, mobile genomic islands that confer methicillin resistance. Importantly, we demonstrate that SCCmec-encoded recombinases mobilize not only SCCmec, but also tandem SCC-like cassettes enriched in genes coding for diverse defense systems. Further, we show that phage infection stimulates cassette mobilization (i.e. excision and circularization). Thus, our findings indicate that SCC/SCCmec cassettes not only spread antibiotic resistance but can also play a role in mobilizing anti-phage defenses.

The CRISPR/Cas system as an antimicrobial resistance strategy in aquatic ecosystems

With the growing population, demand for food has dramatically increased, and fisheries, including aquaculture, are expected to play an essential role in sustaining demand with adequate quantities of protein and essential vitamin supplements, employment generation, and GDP growth. Unfortunately, the incidence of emerging/re-emerging AMR pathogens annually occurs because of anthropogenic activities and the frequent use of antibiotics in aquaculture. These AMR pathogens include the WHO's top 6 prioritized ESKAPE pathogens (nosocomial pathogens: Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.), extended-spectrum beta lactases (ESBLs) and carbapenemase-producing E. coli, which pose major challenges to the biomagnification of both nonnative and native antibiotic-resistant bacteria in capture and cultured fishes. Although implementing the rational use of antibiotics represents a promising mitigation measure, this approach is practically impossible due to the lack of awareness among farmers about the interplay between antimicrobial use and the emergence of antimicrobial resistance (AMR). Nevertheless, to eradicate these 'superbugs,' CRISPR/Cas (clustered regularly interspersed short palindromic repeats/CRISPR associate protein) has turned out to be a novel approach owing to its ability to perform precise site-directed targeting/knockdown/reversal of specific antimicrobial resistance genes in vitro and to distinguish AMR-resistant bacteria from a plethora of commensal aquatic bacteria. Along with highlighting the importance of virulent multidrug resistance genes in bacteria, this article aims to provide a holistic picture of CRISPR/Cas9-mediated genome editing for combating antimicrobial-resistant bacteria isolated from various aquaculture and marine systems, as well as insights into different types of CRISPR/Cas systems, delivery methods, and challenges associated with developing CRISPR/Cas9 antimicrobial agents.

Identification and characterization of SCCmec typing with psm-mec positivity in staphylococci from patients with coagulase-negative staphylococci peritoneal dialysis-related peritonitis

BACKGROUND

Peritonitis is the most important complication of peritoneal dialysis (PD) and coagulase-negative staphylococci (CNS) are a frequent cause of dialysis-related infections. The association between SCCmec typing with psm-mec positivity in staphylococci and PD-related infections has not been identified. We aim to investigate the molecular epidemiology of CNS isolated from PD-peritonitis in a single Chinese center, focusing on the genetic determinants conferring methicillin resistance.

METHODS

We collected 10 genetically unrelated CNS isolates from 10 patients with CNS PD-related peritonitis. The patients were divided into two groups based on the results of MIC to oxacillin: the methicillin-resistant CNS (MRCNS) and methicillin-sensitive CNS (MSCNS) groups. The biofilm formation group (BFG) and the non-biofilm formation group (NBFG) were used as the control groups. Phenotypic and molecular methods were used to analyze SCCmec types I, II and III, associated genes and biofilm formation and the existence of psm-mec. The demographic data and clinical indicators were collected.

RESULTS

Ten CNS PD-related peritonitis patients were enrolled for this study. There were 6 MRCNS and 4 MRCNS isolates. SCCmec types were fully determined in 10 isolates. Seven staphylococci (70%) carried SCCmec, of which 4 isolates carried single SCCmec type I (40%) and 3 isolates had multiple SCCmec elements (I + III). Of the 6 MRCNS isolates, 3 carried SCCmec type I (50%) and 2 isolates carried SCCmec type I + III (33.3%). A high diversity of ccr types, mec complexes and ccr-mec complex combinations was identified among the 10 CNS isolates. The psm-mec gene was detected in 2/10 (20%) CNS isolates. There was no mutation in the psm-mec gene.

CONCLUSIONS

The majority of isolates were hospital-associated isolates. Furthermore, 2 psm-mec positive isolates were MRCNS in the NBFG. The PD patients frequent exposure to hospital would be the main risk factor. The presence of the psm-mec signal in the spectra of the MRCNS tested here demonstrates the presence of certain SCCmec cassettes that convey methicillin resistance.

Prevalence, drug resistance, molecular typing and comparative genomics analysis of MRSA strains from a tertiary A hospital in Shanxi Province, China

Staphylococcus aureus (S. aureus) is an important zoonotic pathogen that causes a high incidence rate and mortality worldwide. This study investigated the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) strains in a tertiary A hospital in Shanxi Province, China, in order to determine the major epidemic clones as well as their antibiotic resistance and virulence characteristics. A total of 212 S. aureus strains were collected in this hospital, and were subjected to antimicrobial susceptibility testing, detection of virulence genes, resistance genes, and efflux pump genes. Among them, 38 MRSA strains were further subjected to detection of biofilm genes, assessment of biofilm formation ability, MLST, spa typing, SCCmec typing, and phylogenetic analysis. The majority of S. aureus strains came from the neonatology department, with secretions and purulent fluid being the main source of samples. The strains showed high resistance to penicillin (98.11%), erythromycin (64.62%) and clindamycin (59.91%), while being sensitive to vancomycin and linezolid. The detection rates of efflux pump genes and resistance genes were high, and there was a significant correlation between resistance gene types and phenotypes, with mecA showing a close correlation with oxacillin. The detection rates of virulence genes and the toxin gene profiles of MSSA and MRSA strains showed significant differences. And the detection rate of biofilm genes in MRSA strains was relatively high, with 13.16% of MRSA strains showing strong biofilm formation ability. The most common epidemic clone of MRSA was ST59-SCCmecIV-t437, followed by ST59-SCCmecV-t437. The former had a higher detection rate of resistance genes and a stronger biofilm formation ability, while the latter had a higher positive rate for pvl gene and stronger pathogenicity, making it more likely to cause systemic infections. Phylogenetic analysis showed that all MRSA strains in this study clustered into three major branches, with distinct differences in antibiotic resistance and virulence characteristics among the branches. ST59-MRSA strains from different species showed consistency and inter-species transmission, but there were differences among ST59-MRSA strains from different geographical locations. In general, most MSSA and MRSA strains exhibited multidrug resistance and carried multiple resistance genes, virulence genes, and biofilm formation genes, warranting further research to elucidate the mechanisms of drug resistance and pathogenesis.

Whole-genome sequencing analysis of molecular epidemiology and silent transmissions causing meticillin-resistant Staphylococcus aureus bloodstream infections in a university hospital

BACKGROUND

The emergence of novel genomic-type clones, such as community-associated meticillin-resistant Staphylococcus aureus (MRSA) and livestock-associated MRSA, and their invasion into hospitals have become major concerns worldwide; however, little information is available regarding the prevalence of MRSA in Japan. Whole-genome sequencing (WGS) has been conducted to analyse various pathogens worldwide. Therefore, it is important to establish a genome database of clinical MRSA isolates available in Japan.

AIM

A molecular epidemiological analysis of MRSA strains isolated from bloodstream-infected patients in a Japanese university hospital was conducted using WGS and single-nucleotide polymorphism (SNP) analysis. Additionally, through a review of patients' clinical characteristics, the effectiveness of SNP analysis as a tool for detecting silent nosocomial transmission that may be missed by other methods was evaluated in diverse settings and various time points of detection.

METHODS

Polymerase-chain-reaction-based staphylococcal cassette chromosome mec (SCCmec) typing was performed using 135 isolates obtained between 2014 and 2018, and WGS was performed using 88 isolates obtained between 2015 and 2017.

FINDINGS

SCCmec type II strains, prevalent in 2014, became rare in 2018, whereas the prevalence of SCCmec type IV strains increased from 18.75% to 83.87% of the population, and became the dominant clones. Clonal complex (CC) 5 CC8 and CC1 were detected between 2015 and 2017, with CC1 being dominant. In 88 cases, SNP analyses revealed nosocomial transmissions among 20 patients which involved highly homologous strains.

CONCLUSIONS

Routine monitoring of MRSA by whole-genome analysis is effective not only for gaining knowledge regarding molecular epidemiology, but also for detecting silent nosocomial transmission.

Progress in the Prevalence, Classification and Drug Resistance Mechanisms of Methicillin-Resistant Staphylococcus aureus

Staphylococcus aureus is a common human pathogen with a variety of virulence factors, which can cause multiple infectious diseases. In recent decades, due to the constant evolution and the abuse of antibiotics, Staphylococcus aureus was becoming more resistant, the infection rate of MRSA remained high, and clinical treatment of MRSA became more difficult. The genetic diversity of MRSA was mainly represented by the continuous emergence of epidemic strains, resulting in the constant changes of epidemic clones. Different classes of MRSA resulted in different epidemics and resistance characteristics, which could affect the clinical symptoms and treatments. MRSA had also spread from traditional hospitals to community and livestock environments, and the new clones established a relationship between animals and humans, promoting further evolution of MRSA. Since the resistance mechanism of MRSA is very complex, it is important to clarify these resistance mechanisms at the molecular level for the treatment of infectious diseases. We firstly described the diversity of SCCmec elements, and discussed the types of SCCmec, its drug resistance mechanisms and expression regulations. Then, we described how the vanA operon makes Staphylococcus aureus resistant to vancomycin and its expression regulation. Finally, a brief introduction was given to the drug resistance mechanisms of biofilms and efflux pump systems. Analyzing the resistance mechanism of MRSA can help study new anti-infective drugs and alleviate the evolution of MRSA. At the end of the review, we summarized the treatment strategies for MRSA infection, including antibiotics, anti-biofilm agents and efflux pump inhibitors. To sum up, here we reviewed the epidemic characteristics of Staphylococcus aureus, summarized its classifications, drug resistance mechanisms of MRSA (SCCmec element, vanA operon, biofilm and active efflux pump system) and novel therapy strategies, so as to provide a theoretical basis for the treatment of MRSA infection.

Tandem mobilization of anti-phage defenses alongside SCCmec cassettes

Bacterial viruses (phages) and the immune systems targeted against them significantly impact bacterial survival, evolution, and the emergence of pathogenic strains. While recent research has made spectacular strides towards discovering and validating new defenses in a few model organisms1-3, the inventory of immune systems in clinically-relevant bacteria remains underexplored, and little is known about the mechanisms by which these systems horizontally spread. Such pathways not only impact the evolutionary trajectory of bacterial pathogens, but also threaten to undermine the effectiveness of phage-based therapeutics. Here, we investigate the battery of defenses in staphylococci, opportunistic pathogens that constitute leading causes of antibiotic-resistant infections. We show that these organisms harbor a variety of anti-phage defenses encoded within/near the infamous SCC (staphylococcal cassette chromosome) mec cassettes, mobile genomic islands that confer methicillin resistance. Importantly, we demonstrate that SCCmec-encoded recombinases mobilize not only SCCmec, but also tandem cassettes enriched with diverse defenses. Further, we show that phage infection potentiates cassette mobilization. Taken together, our findings reveal that beyond spreading antibiotic resistance, SCCmec cassettes play a central role in disseminating anti-phage defenses. This work underscores the urgent need for developing adjunctive treatments that target this pathway to save the burgeoning phage therapeutics from suffering the same fate as conventional antibiotics.

Changes in the Genotypic Characteristics of Community-Acquired Methicillin-Resistant Staphylococcus aureus Collected in 244 Medical Facilities in Japan between 2010 and 2018: a Nationwide Surveillance

Although community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has emerged worldwide, no nationwide CA-MRSA surveillance has been conducted in Japan to determine the changes in its molecular characteristics over time. We aimed to characterize the molecular epidemiology of Panton-Valentine leucocidin (PVL)-positive CA-MRSA strains collected from across Japan in the past decade. We isolated 1,770 MRSA strains from the skin and pus samples of outpatients of 244 medical facilities in 31 prefectures between 2010 and 2018 (2010, 2012, 2014, 2016, and 2018). Regions, hospitals, and periods in which strains were isolated and patient age group and sex were tabulated. Staphylococcal cassette chromosome mec (SCCmec) typing, detection of virulence factor genes, and antimicrobial susceptibility testing were performed. Whole-genome analysis was performed for the PVL-positive strains isolated in 2018. All strains harbored the mecA gene. Compared to that in 2010, the percentage of SCCmec type IV increased in 2018, with a corresponding increase in the proportion of PVL-positive strains (10% to 26%). Of the isolates obtained in 2018, clonal complex 8 (CC8) was dominant among PVL-positive strains. Core-genome single-nucleotide polymorphism analysis, using whole-genome sequencing, suggested that the CC8 PVL-positive strains spread throughout Japan over the last decade. Furthermore, a unique ST22 clone carrying both the PVL- and toxic shock syndrome toxin-1-encoding genes has emerged. We demonstrated that the molecular epidemiology of CA-MRSA in Japan differs from that in Europe and the United States; thus, it is crucial to monitor the trend of changes in CA-MRSA characteristics in Japan.

IMPORTANCE Community-associated MRSA, which is a multidrug-resistant organism and can cause infections in otherwise-healthy individuals, has become a global problem. This paper describes a nationwide surveillance conducted in Japan to investigate changes in molecular epidemiological characteristics of CA-MRSA over the past decade and provides a detailed review of the characteristics of Panton-Valentine leucocidin (PVL)-positive strains isolated in 2018. Although CA-MRSA is rare in Japan to date, we found that the isolation of PVL-positive strains has been increasing over the past decade. In particular, the PVL-positive strains wherein CC8 was dominant exhibited high interstrain similarity, suggesting that a limited number of clones have spread over the past decade. Furthermore, a unique ST22 clone carrying both PVL-encoding and toxic shock syndrome toxin-1-encoding genes has emerged. This study shows that various changes can be observed when molecular epidemiological analysis, combined with next-generation sequencing, is conducted over a long period.

Evaluation of in-house cefoxitin screening broth to determine methicillin-resistant staphylococci

Methicillin-resistant staphylococci (MRS), including methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant coagulase-negative staphylococci (MRCoNS), have a global impact as a public health threat contributing significantly to morbidity, mortality, and socio-economic costs. Accurate and rapid detection of MRS results in effective antimicrobial therapy, immediate patient isolation, dissemination control, and appropriate disinfection measures. Herein, we developed an in-house cefoxitin screening broth and compared it to the cefoxitin disk diffusion method and polymerase chain reaction (PCR) for the detection of MRS. Verification of this screening broth on 52 MRSA, 37 MRCoNS, 44 methicillin-susceptible S. aureus (MSSA), and 11 MSCoNS revealed greater validity for MRSA/MSSA than for MRCoNS/MSCoNS. The kappa coefficient of 0.87 was superior for determination of MRSA and MSSA, whereas it was 0.54, which was considered poor, for determination of MRCoNS and MSCoNS. Application of this assay to screen MRSA should be useful in clinical laboratories and hospital infection-control units.

Current Status of Staphylococcal Cassette Chromosome mec (SCCmec)

Staphylococcal cassette chromosome mec (SCCmec) typing was established in the 2000s and has been employed as a tool for the molecular epidemiology of methicillin-resistant Staphylococcus aureus, as well as the evolution investigation of Staphylococcus species. Molecular cloning and the conventional sequencing of SCCmec have been adopted to verify the presence and structure of a novel SCCmec type, while convenient PCR-based SCCmec identification methods have been used in practical settings for many years. In addition, whole-genome sequencing has been widely used, and various SCCmec and similar structures have been recently identified in various species. The current status of the SCCmec types, SCCmec subtypes, rules for nomenclature, and multiple methods for identifying SCCmec types and subtypes were summarized in this review, according to the perspective of the International Working Group on the Classification of Staphylococcal Cassette Chromosome Elements.

Whole-Genome Sequencing and Machine Learning Analysis of Staphylococcus aureus from Multiple Heterogeneous Sources in China Reveals Common Genetic Traits of Antimicrobial Resistance

Staphylococcus aureus is a worldwide leading cause of numerous diseases ranging from food-poisoning to lethal infections. Methicillin-resistant S. aureus (MRSA) has been found capable of acquiring resistance to most antimicrobials. MRSA is ubiquitous and diverse even in terms of antimicrobial resistance (AMR) profiles, posing a challenge for treatment. Here, we present a comprehensive study of S. aureus in China, addressing epidemiology, phylogenetic reconstruction, genomic characterization, and identification of AMR profiles. The study analyzes 673 S. aureus isolates from food as well as from hospitalized and healthy individuals. The isolates have been collected over a 9-year period, between 2010 and 2018, from 27 provinces across China. By whole-genome sequencing, Bayesian divergence analysis, and supervised machine learning, we reconstructed the phylogeny of the isolates and compared them to references from other countries. We identified 72 sequence types (STs), of which, 29 were novel. We found 81 MRSA lineages by multilocus sequence type (MLST), spa, staphylococcal cassette chromosome mec element (SCCmec), and Panton-Valentine leukocidin (PVL) typing. In addition, novel variants of SCCmec type IV hosting extra metal and antimicrobial resistance genes, as well as a new SCCmec type, were found. New Bayesian dating of the split times of major clades showed that ST9, ST59, and ST239 in China and European countries fell in different branches, whereas this pattern was not observed for the ST398 clone. On the contrary, the clonal transmission of ST398 was more intermixed in regard to geographic origin. Finally, we identified genetic determinants of resistance to 10 antimicrobials, discriminating drug-resistant bacteria from susceptible strains in the cohort. Our results reveal the emergence of Chinese MRSA lineages enriched of AMR determinants that share similar genetic traits of antimicrobial resistance across human and food, hinting at a complex scenario of evolving transmission routes. IMPORTANCE Little information is available on the epidemiology and characterization of Staphylococcus aureus in China. The role of food is a cause of major concern: staphylococcal foodborne diseases affect thousands every year, and the presence of resistant Staphylococcus strains on raw retail meat products is well documented. We studied a large heterogeneous data set of S. aureus isolates from many provinces of China, isolated from food as well as from individuals. Our large whole-genome collection represents a unique catalogue that can be easily meta-analyzed and integrated with further studies and adds to the library of S. aureus sequences in the public domain in a currently underrepresented geographical region. The new Bayesian dating of the split times of major drug-resistant enriched clones is relevant in showing that Chinese and European methicillin-resistant S. aureus (MRSA) have evolved differently. Our machine learning approach, across a large number of antibiotics, shows novel determinants underlying resistance and reveals frequent resistant traits in specific clonal complexes, highlighting the importance of particular clonal complexes in China. Our findings substantially expand what is known of the evolution and genetic determinants of resistance in food-associated S. aureus in China and add crucial information for whole-genome sequencing (WGS)-based surveillance of S. aureus.

Staphylococcus saprophyticus Causing Infections in Humans Is Associated with High Resistance to Heavy Metals

Staphylococcus saprophyticus is a common pathogen of the urinary tract, a heavy metal-rich environment, but information regarding its heavy metal resistance is unknown. We investigated 422 S. saprophyticus isolates from human infection and colonization/contamination, animals, and environmental sources for resistance to copper, zinc, arsenic, and cadmium using the agar dilution method. To identify the genes associated with metal resistance and assess possible links to pathogenicity, we accessed the whole-genome sequence of all isolates and used in silico and pangenome-wide association approaches. The MIC values for copper and zinc were uniformly high (1,600 mg/liter). Genes encoding copper efflux pumps (copA, copB, copZ, mco, and csoR) and zinc transporters (zinT, czrAB, znuBC, and zur) were abundant in the population (20 to 100%). Arsenic and cadmium showed various susceptibility levels. Genes encoding the ars operon (arsRDABC), an ABC transporter and a two-component permease, were linked to resistance to arsenic (MICs ≥ 1,600 mg/liter; 14% [58/422]; P < 0.05). At least three cad genes (cadA or cadC and cadD-cadX or czrC) and genes encoding multidrug efflux pumps and hyperosmoregulation in acidified conditions were associated with resistance to cadmium (MICs ≥ 200 mg/liter; 20% [85/422]; P < 0.05). These resistance genes were frequently carried by mobile genetic elements. Resistance to arsenic and cadmium were linked to human infection and a clonal lineage originating in animals (P < 0.05). Altogether, S. saprophyticus was highly resistant to heavy metals and accumulated multiple metal resistance determinants. The highest arsenic and cadmium resistance levels were associated with infection, suggesting resistance to these metals is relevant for S. saprophyticus pathogenicity.

Molecular characteristics of Staphylococcus aureus strains isolated from nasal samples of sixth year medical students during their pediatric services practices

Background

Methicillin-resistant Staphylococcus aureus (MRSA) strains are prevalent in healthcare services. Medical students are at risk for MRSA carriage, subsequent infection and potential transmission of nosocomial infection.Few studies have examined MRSA carriage among medical students.

Methods

In this prospective cohort study, between July 2016 and June 2017, two nasal swab samples were taken per student 4 weeks apart during their pediatric internship. MRSA typing was performed by staphylococcal cassette chromosome mec (SCCmec) types, Panton Valentine leukocidin (PVL) encoding genes.

Results

A total of 239 sixth year medical students, 164 (68.6%) male (M/F:2.1),with median age 25 years (min–max; 23–65 years) were included in this prospective cohort study. Among 239 students, 17 students (7.1%) were found to be colonized with methicillin-sensitive S. aureus (MSSA) at the beginning of pediatric internship. After 4 weeks, at the end of pediatric internship totally 52 students were found to be S. aureus colonized (21.8%). Three of 52 S. aureus isolates were MRSA (1.3%) and the rest was MSSA (20.5%), all were PVL gen negative. Two of three MRSA isolates were characterized as SCCmec type IV, one isolate was untypeable SCCmec. Nasal carriage of S. aureus increased from 7.1% to 21.5% (p < 0.001). Nasal S. aures colonization ratio was higher in students working in pediatric infectious disease service (p = 0.046). Smoking was found to be associated with a 2.37-fold [95% CI (1.12–5.00); p = 0.023] and number of patients in pediatric services was 2.66-fold [95% CI (1.13–6.27); p = 0.024] increase the risk of nasal S. aureus colonization. Gender was not found to increase risk of MRSA carriage.

Conclusion

MSSA nasal carriage increased at the end of pediatric internship and significantly high in students working in pediatric infectious diseases services. Smoking and high number of patients in pediatric services significantly increase S.aureus colonization.

Increased Incidence and Plasma-Biofilm Formation Ability of SCCmec Type IV Methicillin-Resistant Staphylococcus aureus (MRSA) Isolated From Patients With Bacteremia

In Japan, Staphylococcal cassette chromosome mec (SCCmec) type IV methicillin-resistant Staphylococcus aureus (MRSA) is an increasingly prominent cause of bacteremia, but the virulence of most of these strains is unclear. We aimed to investigate the relationship between the molecular characteristics and the ability to form biofilms in the presence of blood plasma (plasma-biofilms) of MRSA strains isolated from bloodstream infections. In this study, the molecular characteristics and biofilms of MRSA strains isolated from blood cultures between 2015 and 2017 were analyzed by PCR-based assays, crystal violet staining, and confocal reflection microscopy methods. Among the 90 MRSA isolates, the detection rate of SCCmec type II clones decreased from 60.7 to 20.6%. The SCCmec type IV clone replaced the SCCmec type II clone as the dominant clone, with a detection rate increasing from 32.1 to 73.5%. The plasma-biofilm formation ability of the SCCmec type IV clone was higher than the SCCmec type II clone and even higher in strains harboring the cna or arcA genes. Plasma-biofilms, mainly composed of proteins, were formed quickly and strongly. Our study demonstrated the increased plasma-biofilm formation ability of SCCmec type IV strains.

Two Cases of Intrafamilial Transmission of Community-Acquired Methicillin-Resistant Staphylococcus aureus Producing Both PVL and TSST-1 Causing Fatal Necrotizing Pneumonia and Sepsis

Introduction

Staphylococcus aureus produces numerous toxins, such as toxic shock syndrome toxin 1 (TSST-1) and Panton–Valentine leukocidin (PVL). We isolated community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) strains producing both TSST-1 and PVL isolated from severe necrotizing pneumonia cases in a Nepali family. Detection of these CA-MRSA strains is rare in the world, and infection with these strains can take a rapidly progressive and lethal course. In this study, we traced the clinical course of this case and conducted a genetic analysis of the isolated strains.

Case Report

We described 2 familial cases (a 20-year-old male and 61-year-old female) of severe necrotizing pneumonia caused by CA-MRSA with the TSST-1 and PVL genes. A 20-year-old Nepalese male was admitted to our hospital after a 3-day history of high fever and coughing. Despite resuscitation efforts, he died of multiple organ failure. A 61-year-old Nepalese female was admitted to our hospital with a complaint of high fever and dyspnea for 1 day. She was the grandmother of the male subject and mostly stayed at his residence in Japan. We administered intravenous antibiotics, including anti-MRSA antibiotics, and she improved in 2 weeks. The sequence type of the isolates was ST22/SCCmec type IVa, and the spa type was t005. The virulence genes detected were as follows: PVL gene (lukSF-pv), TSST-1 gene (tst-1), sec, seg, sei, sel, sem, sen, seo, and seu. ST22 was not the dominant CA-MRSA clone type in Japan. Some of the reports demonstrated that PVL-/TSST-1-positive ST22-MRSA strains are prevalent in Nepal. Therefore, the MRSA strains were thought to be acquired from Nepal.

Conclusion

These cases highlight the emergence of TSST-1- and PVL-positive CA-MRSA infection and its association with life-threatening community-acquired necrotizing pneumonia. Clinicians should note the possibility of introducing MRSA strains from abroad and be aware of this illness to initiate appropriate treatment.