Molecular identification and genotyping of MRSA isolates

The aim of this study was to identify and characterize 97 methicillin-resistant Staphylococcus aureus (MRSA) isolates. Two conventional multiplex PCR assays, a real-time PCR assay and two PCR-based genotyping techniques including the spa - and hypervariable region (HVR)-typing methods were used to identify and characterize 97 MRSA strains isolated between April 2006 to September 2007 from the Steve Biko Academic Hospital. All MRSA isolates were positive for 16S rRNA gene, 99% were positive for the mec A gene and 4% positive for the Panton–Valentine leukocidin (PVL) gene. Staphylococcal cassette chromosome mec (SCC mec ) typing showed 67% of isolates were SCC mec II [health-care-associated MRSA (HA-MRSA)], 14% were SCC mec III (HA-MRSA) and 4% were SCC mec IVd [community-associated MRSA (CA-MRSA)]. These CA-MRSA isolates showed a prevalence of 100% for the PVL gene. Using spa typing, three distinct clusters could be identified while HVR typing revealed six different clusters. CA-MRSA isolates were clustered together using spa and HVR typing. This study showed the prevalence of the CA-MRSA strains, PVL genes, the SCC mec types and the clonality of the MRSA strains. The high prevalence of the PVL gene in CA-MRSA isolates already residing in intensive care units was alarming and indicated the emergence of new MRSA lineages with a particular fitness for community and hospital transmission.     

Comparative genomics and drug resistance of a geographic variant of ST239 methicillin-resistant Staphylococcus aureus emerged in Russia

Two distinct classes of methicillin-resistant Staphylococcus aureus (MRSA) are spreading in hospitals (as hospital-acquired MRSA, HA-MRSA) and in the community (as community-acquired MRSA, CA-MRSA). Multilocus sequence type (ST) 239 MRSA, one of the most worldwide-disseminated lineages, has been noted as a representative HA-MRSA. Here, we isolated ST239 MRSA (spa type 3 [t037] and staphylococcal cassette chromosome mec [SCCmec] type III.1.1.1) and its novel variant with ST239/spa351 (t030)/SCCmecIII.1.1.4 (SCCmecIII(R)) not only from hospitals but also from patients with urethritis in the community in Russia. The Russian variant (strain 16K) possessed a hybrid genome consisting of CC8 and CC30, similar to the ST239/spa3/SCCmecIII.1.1.1 HA-MRSA (TW20) genome, but with marked diversity. The 16K' CC30 section had SCCmecIII(R) carrying the dcs-carrying unit (which corresponded to the SCCmecIVc J3 joining region of ST30 CA-MRSA), lacked SCCmercury, and possessed a novel mobile element structure (MES16K) carrying the ccrC-carrying unit (with the recombinase gene ccrC1 allele 3) and drug resistance tranposons. The Russian variant included strains with a high ability to transfer its multiple drug resistance by conjugation; e.g., for strain 16K, the transfer frequency of a chloramphenicol resistance plasmid (p16K-1 with 2.9 kb in size) reached 1.4×10(-2), followed by Tn554 conjugative transfer at 3.6×l0(-4). The Russian variant, which has been increasing recently, included divergent strains with different plasmid patterns and pulsed field gel electrophoresis profiles. The data demonstrate the alternative nature of ST239 MRSA as CA-MRSA and also as a drug resistance disseminator, and its micro but dynamic evolution in Russia.     

Polyclonal non multiresistant Staphylococcus aureus isolates from clinical cases of infection occurring in Palermo, Italy, during a one-year surveillance period

ABSTRACT: BACKGROUND: The evolving epidemiology of methicillin resistant Staphylococcus aureus (MRSA) is characterized by the emergence of infections caused by non multiresistant MRSA carrying staphylococcal chromosomal cassette (SCC)mec IV or V in the healthcare settings. A molecular epidemiological analysis of non multiresistant MRSA isolates from four acute general hospitals was performed in Palermo, Italy, during a one year period. METHODS: For the purpose of the study, MRSA isolates were defined as non multiresistant when they were susceptible to at least three classes of non beta-lactam antibiotics. Seventy-five isolates were submitted to antimicrobial susceptibility testing, multilocus sequence typing (MLST) and polymerase chain reaction (PCR) for SCCmec, accessory gene regulator (agr) groups, arginine catabolic mobile element (ACME) and Panton Valentine leukocidin (PVL) toxin genes. For epidemiological typing, Multiple-Locus Variable-Number Tandem Repeat Fingerprinting (MLVF) was performed on all isolates and pulsed field gel electrophoresis (PFGE) on ST8 isolates. RESULTS: Non multiresistant MRSA isolates were isolated from all hospitals. Resistances to ciprofloxacin, macrolides and tetracycline were the most prevalent. MLST attributed 46 isolates with ST22, 13 with ST8, eight with ST1, three with ST50 and three with ST398. SCCmec type IV was found in all isolates. PVL was detected in one ST22 isolate. All isolates tested negative for the ACME element. MLVF identified 31 different patterns, some subtype clusters ranging in size between two and 22 isolates. The closely related PFGE patterns of the ST8 isolates differed from USA300. CONCLUSIONS: A polyclonal circulation of non multiresistant MRSA along with blurring of boundaries between healthcare associated (HA)-MRSA and community associated (CA)-MRSA appear to be occurring in our epidemiological setting. A better understanding of spread of MRSA with the support of molecular typing can provide invaluable information in the epidemiological, microbiological and clinical fields.     

A study of the polymorphism of mec dna in methycillin-resistant strains of Staphylococcus aureus isolated at permanent stations in different regions of Russia

Polymorphism of the chromosome staphylococcus cassette mec (SCCmec), a mobile and heterological genetic element providing resistance to beta-lactam antibiotics was studied in methycillin-resistant strains of Staphylococcus aureus (MRSA) isolated at permanent stations situated in different regions of Russia. Type SCCmec was identified using the PCR method by determining allotypes of 3 different structural genetic complexes incorporated in the cassettes mec. It was found that the isolates studied in this work contained 3 different types of SCCmec: I, III, and IVb. Both isolates containing 2 different copies of SCCmec and isolates containing defective copies of SCCmec were identified. It was demonstrated that determination of the SCC-mec type provided an opportunity to differentiate the isolates studied in this work from one another. The isolates attributed to the same genotype variant (identified by polymorphism of coagulase gene) but isolated at different hospitals located in different regions of Russia were found to contain the same type of the chromosome staphylococcus cassette mec, whereas the isolates of different coagulase groups (i.e., different genotype variants) contained different types of SCCmec. It was found that at least 2 epidemic strains circulated in the permanent hospitals of Russia. The strains differ from one another by the polymorphism of the coagulase gene and the mec DNA polymorphism. According to results of studies of several molecular markers (including mec DNA), these strains proved to be identical to the international strains EMRSA-1 and EMRSA-2. Possible mechanisms of MRSA formation and circulation in Russia and CIS countries are discussed.     

Identification in methicillin-susceptible Staphylococcus hominis of an active primordial mobile genetic element for the staphylococcal cassette chromosome mec of methicillin-resistant Staphylococcus aureus

We previously reported that the methicillin resistance gene mecA is carried by a novel type of mobile genetic element, SCCmec (staphylococcal cassette chromosome mec), in the chromosome of methicillin-resistant Staphylococcus aureus (MRSA). These elements are precisely excised from the chromosome and integrated into a specific site on the recipient chromosome by a pair of recombinase proteins encoded by the cassette chromosome recombinase genes ccrA and ccrB. In the present work, we detected homologues of the ccr genes in Staphylococcus hominis type strain GIFU12263 (equivalent to ATCC 27844), which is susceptible to methicillin. Sequence determination revealed that the ccr homologues in S. hominis were type 1 ccr genes (ccrA1 and ccrB1) that were localized on a genetic element structurally very similar to SCCmec except for the absence of the methicillin-resistance gene, mecA. This genetic element had mosaic-like patterns of homology with extant SCCmec elements, and we designated it SCC(12263) and considered it a type I staphylococcal cassette chromosome (SCC). The ccrB1 gene identified in the S. hominis strain is the first type 1 ccrB gene discovered to retain its function through the excision process as judged by two criteria: (i) SCC(12263) was spontaneously excised during cultivation of the strain and (ii) introduction of the S. hominis ccrB1 into an MRSA strain carrying a type I SCCmec whose ccrB1 gene is inactive generated SCCmec excisants at a high frequency. The existence of an SCC without a mec determinant is indicative of a staphylococcal site-specific mobile genetic element that serves as a vehicle of transfer for various genetic markers between staphylococcal species.     

Extensive Dissemination of Methicillin-Resistant Staphylococcus aureus (MRSA) between the Hospital and the Community in a Country with a High Prevalence of Nosocomial MRSA

According to the EARS-Net surveillance data, Portugal has the highest prevalence of nosocomial methicillin-resistant Staphylococcus aureus (MRSA) in Europe, but the information on MRSA in the community is very scarce and the links between the hospital and community are not known. In this study we aimed to understand the events associated to the recent sharp increase in MRSA frequency in Portugal and to evaluate how this has shaped MRSA epidemiology in the community. With this purpose, 180 nosocomial MRSA isolates recovered from infection in two time periods and 14 MRSA isolates recovered from 89 samples of skin and soft tissue infections (SSTI) were analyzed by pulsed-field gel electrophoresis (PFGE), staphylococcal chromosome cassette mec (SCCmec) typing, spa typing and multilocus sequence typing (MLST). All isolates were also screened for the presence of Panton Valentine leukocidin (PVL) and arginine catabolic mobile element (ACME) by PCR. The results showed that ST22-IVh, accounting for 72% of the nosocomial isolates, was the major clone circulating in the hospital in 2010, having replaced two previous dominant clones in 1993, the Iberian (ST247-I) and Portuguese (ST239-III variant) clones. Moreover in 2010, three clones belonging to CC5 (ST105-II, ST125-IVc and ST5-IVc) accounted for 20% of the isolates and may represent the beginning of new waves of MRSA in this hospital. Interestingly, more than half of the MRSA isolates (8/14) causing SSTI in people attending healthcare centers in Portugal belonged to the most predominant clones found in the hospital, namely ST22-IVh (n = 4), ST5-IVc (n = 2) and ST105-II (n = 1). Other clones found included ST5-V (n = 6) and ST8-VI (n = 1). None of the MRSA isolates carried PVL and only five isolates (ST5-V-t179) carried ACME type II. The emergence and spread of EMRSA-15 may be associated to the observed increase in MRSA frequency in the hospital and the consequent spillover of MRSA into the community.     

Characterization of methicillin-resistant Staphylococcus aureus isolates from food and food products of poultry origin in Germany

During a survey of fresh chicken and turkey meat as well as chicken and turkey meat products for the presence of methicillin-resistant Staphylococcus aureus (MRSA) isolates in Germany, 32 (37.2%) of 86 samples were MRSA positive. Twenty-eight of these MRSA isolates belonged to clonal complex 398 (CC398), which is widespread among food-producing animals. These CC398 isolates carried SCCmec elements of type IV or V and exhibited spa type t011, t034, t899, t2346 or t6574 and either the known dru types dt2b, dt6j, dt10a, dt10q, dt11a, dt11v, and dt11ab or the novel dru types dt6m, dt10as, and dt10at. In addition, two MRSA sequence type 9 (ST9) isolates with a type IV SCCmec cassette, spa type t1430, and dru type dt10a as well as single MRSA ST5 and ST1791 isolates with a type III SCCmec cassette, spa type t002, and dru type dt9v were identified. All but two isolates were classified as multiresistant. A wide variety of resistance phenotypes and genotypes were detected. All isolates were negative for the major virulence factors, such as Panton-Valentine leukocidin, toxic shock syndrome toxin 1, or exfoliative toxins. In contrast to the MRSA CC398 isolates, the four ST9, ST5, or ST1791 isolates harbored the egc gene cluster for enterotoxin G, I, M, N, O, and U genes. Although the relevance of contamination of fresh poultry meat or poultry products with MRSA is currently unclear, the presence of multiresistant and, in part, enterotoxigenic MRSA emphasizes the need for further studies to elucidate possible health hazards for consumers.     

金黄色葡萄球菌所致肺部感染的耐药特点及其Panton—Valentine杀白细胞素基因的携带状况分析

目的分析金黄色葡萄球菌所致肺部感染的耐药性特点及其Panton—Valentine杀白细胞素基因的携带状况。方法回顾性调查了温州医学院第一附属医院2005年1月至2006年1月医院感染的金黄色葡萄球菌所致肺部感染患者132例,对其体外药敏试验进行分析;并利用多重PCR检测其PVL基因,应用多位点基因序列分型（multilocus sequence typing,MLST）技术对PVL基因阳性的菌株进行序列分型。耐甲氧西林金黄色葡萄球菌（methicillin-resistant Staphylococcus aureus,MRSA）的SCCmec基因分型采用多重聚合酶链反应。结果致肺部感染的132株金黄色葡萄球菌的耐药现象较为严重,仅对万古霉素、呋喃妥因及复方新诺明等药物的敏感率较高;其中经多重PCR筛选出10株携带PVL基因的金葡菌,全部为MRSA菌株,3株为ST239-SCCⅢ,2株为ST398-SCCmecⅢ,2株为ST398-SCCmecⅣ,ST25-SCCmecⅢ、ST59-SCCmecⅠ和ST88-SCCmecⅢ各1株。结论肺部感染的金黄色葡萄球菌对多种抗生素耐药,呈多重耐药性;其携带PVL基因占一定比例。     

The emergence and evolution of methicillin-resistant Staphylococcus aureus

Significant advances have been made in recent years in our understanding of how methicillin resistance is acquired by Staphylococcus aureus. Integration of a staphylococcal cassette chromosome mec (SCCmec) element into the chromosome converts drug-sensitive S. aureus into the notorious hospital pathogen methicilin-resistant S. aureus (MRSA), which is resistant to practically all beta-lactam antibiotics. SCCmec is a novel class of mobile genetic element that is composed of the mec gene complex encoding methicillin resistance and the ccr gene complex that encodes recombinases responsible for its mobility. These elements also carry various resistance genes for non-beta-lactam antibiotics. After acquiring an SCCmec element, MRSA undergoes several mutational events and evolves into the most difficult-to-treat pathogen in hospitals, against which all extant antibiotics including vancomycin are ineffective. Recent epidemiological data imply that MRSA has embarked on another evolutionary path as a community pathogen, as at least one novel SCCmec element seems to have been successful in converting S. aureus strains from the normal human flora into MRSA.     

Diversity of staphylococcal cassette chromosome in coagulase-negative staphylococci from animal sources

Aims:  To type the staphylococcal cassette chromosome (SCC) in coagulase-negative staphylococci (CoNS) from animal sources.
Methods and Results:  A total of 92 CoNS isolates recovered from farm animals was analysed. The top three staphylococcal species were Staphylococcus lentus (34), S. sciuri (31), and S. xylosus (13). The presence of the cassette chromosome recombinase (ccr) genes ccrA1 , ccrB1 , ccrA2 , ccrB2 , ccrA3 , ccrB3 and ccrC , the mec regulatory genes mecI and mecR1 , and Tn 554 was used to differentiate the SCC. A total of 60 of the 92 isolates were methicillin resistant. Among the 60 methicillin-resistant Staphylococcus spp. isolates, SCC mec ( mecA -carrying SCC) types I, III, IV and V were identified in 24 isolates based on the combinations of the ccr genes and the mec regulatory genes, with type III being predominant. The single S. epidermidis carried SCC mec type IV. SCC type III was also identified in two of 32 methicillin-susceptible isolates. Identical SCC mec types were present in different species of CoNS. Pulsed-field gel electrophoresis (PFGE) generated 64 patterns out of 81 PFGE typeable isolates. Indistinguishable clones were detected in animals from different farms.
Conclusions:  Heterogeneous SCC existed in CoNS of diverse genetic background. Both clonal transmission of methicillin-resistant CoNS and horizontal transfer of SCC mec occurred in the animal production environment.
Significance and Impact of the Study:  This study adds to our knowledge of SCC mec type and the diversity of SCC in CoNS.     

Characteristics of the community-genotype sequence type 72 methicillin-resistant <Emphasis Type="Italic">Staphylococcus aureus</Emphasis> isolates that underlie their persistence in hospitals

Panton-Valentine leukocidin-negative methicillin-resistant Staphylococcus aureus (MRSA) clone ST72, known as a major community-associated MRSA in Korea, has emerged as an important pathogen in hospitals. To understand bacterial properties that underlie transformation of this clone into a nosocomial pathogen, we compared characteristics of the community-genotype ST72 MRSA isolates with those of ST5 and ST239 MRSA, which have been predominant nosocomial MRSA clones in Korea. Several genes associated with adhesion and virulence were absent or rarely found in ST72 isolates. Many ST72 isolates (70.1%) belonged to agr group I, but the agr group of other ST72 isolates could not be determined. As indicated by d-hemolysin production, ST72 isolates expressed fully functional agr, whereas agr dysfunction was observed in ST5 and ST239 isolates. In the biofilm formation assay, no upregulation of biofilm-forming activity of ST72 MRSA was detected. However, ST72 isolates demonstrated persistence under hypotonic and desiccating conditions (survival rates 72.3% and 33.9%, respectively), which was similar to characteristics of ST5 or ST239 isolates. ST72- MRSA isolates showed low virulence, but properties of their functional agr system could facilitate their spread in hospitals. In conclusion, tolerance to stressful environments, e.g., hypotonic and dry conditions, may also contribute to survival of the community-associated MRSA clones in healthcare facilities.     

SCCmec遗传元件及其在耐甲氧西林金黄色葡萄球菌分子分型中的应用

携带mec基因簇的葡萄球菌盒式染色体(Staphylococcal chromosome cassette mec, SCCmec)遗传元件的获得是耐甲氧西林金黄色葡萄球菌(Methicillin-resistant Staphylococcus aureus, MRSA)耐药的主要原因。SCCmec由一个mec基因簇、一个染色体重组酶(ccr)基因簇及3个J区组成。mec基因簇含有mecA及其调控基因,mecA基因编码的耐药决定簇使MRSA对β-内酰胺类抗生素耐药;ccr基因簇编码的重组酶负责SCCmec元件的整合与切离;J区差异大,导致不同来源MRSA菌株携带SCCmec的大小不一,在组成上也具有多样性。这些特征为利用SCCmec元件进行MRSA分型创造了条件。文章介绍了SCCmec元件的结构和功能,综述了基于SCCmec的MRSA分型研究。     

Bridges from hospitals to the laboratory: genetic portraits of methicillin-resistant Staphylococcus aureus clones

Methicillin-resistant Staphylococcus aureus (MRSA) emerged in the early 1960's after the acquisition of the methicillin resistance gene mecA, which is carried by the staphylococcal cassette chromosome mec (SCCmec). MRSA seemed to have arisen by multiple introductions of SCCmec into successful methicillin-susceptible S. aureus (MSSA) lineages. MRSA is one of the most common agents of nosocomial infections worldwide increasing the cost and mortality compared to MSSA infections. Little by little, MRSA has acquired resistance to all antibiotics available in clinical practice, which complicates treatment. This situation was further aggravated by the recent reports of vanA-mediated vancomycin-resistant S. aureus. As a reaction to the emergence and spread of multidrug-resistant MRSA worldwide, international surveillance systems such as the CEM/NET initiative have been created. The characterization of over 3000 MRSA isolates from different regions of the world evidenced the existence of only a few epidemic clones spread worldwide, namely the Iberian, Brazilian, Hungarian, New York/Japan, Pediatric and EMRSA-16 clones. It was found that in surveillance or evolutionary studies strains should be characterized by a combination of different typing methods, namely pulsed-field gel electrophoresis, multi-locus sequence typing and SCCmec typing. In recent years, community-acquired MRSA (CA-MRSA) has become a growing public health concern. However, although many authors reported the emergence of CA-MRSA isolates, a standard definition has not been created and the prevalence of MRSA among persons without risk factors seems to remain very low. CA-MRSA has distinct properties compared to epidemic nosocomial clones and its origin is still unclear. Certain authors suggest there is MRSA transmission from the hospital setting to the community, namely transfer of nosocomial MRSA minor clones or sporadic isolates showing a high degree of similarity with CA-MRSA; others believe CA-MRSA strains represent new acquisitions of SCCmec DNA in susceptible backgrounds. Many questions concerning this extraordinarily versatile and threatening pathogen remain unanswered, needing future investigation     

Molecular characterization of methicillin-resistant Staphylococcus aureus in hospitals in Niigata, Japan: divergence and transmission

The major methicillin-resistant Staphylococcus aureus(MRSA) distributed among hospitals in Japan is New York/Japan clone [multilocus sequence type 5 (ST5), agr type 2 and methicillin resistance locus type (SCC mec) II] which possesses both the toxic shock syndrome toxin 1 gene (tst) and staphylococcal enterotoxin C gene (sec). In this study, we collected 245 MRSA strains from four hospitals during 2001 to 2005 in Niigata, Japan, and analyzed tst and sec genes and SCC mec type among them. A total of 13 strains were further examined for their genotypes, virulence gene patterns and drug resistance. Among the 245 strains four tst sec genes patterns were observed; tst(+) sec(+) strains represented a majority of 86.5% and 9.4% were tst(-) sec(-). SCCmec typing revealed that 91.4% had type II, 4.1% type IV and 4.1% type I. Multilocus sequence typing (MLST) revealed that 10 of the 13 typed strains belonged to clonal complex 5 (7 had ST5 while 3 were single locus variants of ST5) with similar characteristics to the New York/Japan clone and possessed multi-drug resistance with high virulence gene content. The remaining 3 strains were ST8 (n=2) and ST91 (n=1). The ST91 strain had SCC mec IV and seemed to originate in the community, while ST8 strains exhibited SCC mec type I, which is distinct from community type IV. The data suggest that MRSA in hospitals in Niigata now mainly includes the New York/Japan clone (undergoing genomic divergence and clonal expansion) and other minor types (e.g. ST8) as well as the community type.     

耐甲氧西林金黄色葡萄球菌的两种新SCCmec型别及其抗药性研究

为探明本地区耐甲氧西林金黄色葡萄球菌(Staphylococcusaureus)的耐药性、流行病学分布状况及携带的葡萄球菌染色体mec盒(SCCmec)型别,用K-B琼脂扩散法、E-test和多位点PCR,对临床分离的金黄色葡萄球菌菌株进行了SCCmec分型及耐药性测定。结果发现了两种新的SCCmec型别,新1型含Ⅱ型的mecA上游特异性位点B和位于mecA内的M位点以及Ⅲ型的下游位点F,缺乏Ⅱ型上游位点C和下游位点D、G;新2型含Ⅰ、Ⅱ型的上游特异性位点A、B和两个Ⅲ型的下游位点F、H,同样缺乏位点C、D、G,可能分别为原有Ⅱ型和Ⅰ、Ⅱ型与Ⅲ型的基因重组株;且携带有新SCCmec型别的MRSA菌株,其流行病学分布特点及抗药性也与国外已报导的菌株不同,多分自门诊病人,且耐药性高,抗药谱广,值得引起高度重视和关注。     

Integron-bearing methicillin-resistant coagulase-negative staphylococci in South China, 2001–2004

A total of 53 methicillin-resistant coagulase-negative staphylococci strains isolated in a hospital in Guangzhou, China, were analyzed to detect class 1 integrons and SCC mec typing. Thirty strains had the class 1 integrase ( intI1 ) gene and 26 strains possessed the 3' conserved region of qacE Δ 1 - sul1 . Four different types of gene cassette arrays were found and a highly prevalent array of dfrA12-orfF-aadA2 gene cassettes was observed. Thirty class 1 integron-positive coagulase-negative staphylococci strains were subjected to Southern hybridization analysis; the result showed that class 1 integrons were located on chromosome, not plasmid. According to the results of SCC mec typing for 30 integron-bearing MRCNS strains, five, 15 and five strains belonged to type I, II and III SCC mec , respectively, and five strains were untypeable. For 23 non-integron-bearing methicillin-resistant coagulase-negative staphylococci strains, four, nine and seven strains belonged to type I, II and III SCC mec , respectively, and three strains were untypeable. None of the strains belonged to type IV or V. Twenty-three coagulase-negative staphylococci isolates of three Staphylococcal species that contained the dfrA12-orfF-aadA2 gene cassette array were phylogenetically unrelated to each other by randomly amplified polymorphic DNA, indicating that the gene cassettes might be disseminated in the clinical strains by a horizontal gene transfer.     

Community-acquired methicillin resistantStaphylococcus aureus isolated in dermatology department

Community-acquired methicillin-resistantStaphylococcus aureus (CA-MRSA) strains, known as a nosocomial pathogen, have emerged in the community worldwide. CA-MRSA infects frequently young children and is implicated in skin and soft tissue infections. In the present study, we reported the isolation of CA-MRSA strains from elderly patients admitted to the dermatology department at University Hospital of Monastir. The relatedness of these isolates was investigated by PFGE typing which indicated that all strains were clonally related. MRSA strains were thoroughly characterized by molecular methods which revealed that all isolates possessed the unique sequence type ST80 as well as a single spa type t044. Whole genotypic results suggest that all isolates were PVL producing CA-MRSA and were closely related and belonging to the ST80 clone.     

Commercially distributed meat as a potential vehicle for community-acquired methicillin-resistant Staphylococcus aureus

The incidence of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infection has been increasing; however, the sources of infection remain unclear. Therefore, we investigated the involvement of meat as a possible mediator of CA-MRSA infection. We examined the distribution of MRSA strains in commercially distributed raw meat samples (n = 197) and diarrheal stool samples of outpatients (n = 1,287) that were collected in Oita Prefecture, Japan, between 2003 and 2009 for routine legal inspections. Fourteen MRSA strains were isolated from three meat and 11 stool samples. Among these, seven isolates from three meat and four stool samples exhibited the same epidemiological marker profiles [coagulase type III, staphylococcal enterotoxin C, staphylococcal chromosomal cassette mec (SCCmec) type IV, ST8, spa type 606 (t1767), and toxic shock syndrome toxin-1 (TSST-1) producing type]. Furthermore, of the seven strains, three isolates from two meat samples and one stool sample collected in 2007 exhibited completely identical characteristics with respect to phage open reading frame (ORF) typing, pulsed-field gel electrophoresis, and drug susceptibility profiles. The results suggest that commercially distributed meat could play a role in the prevalence of CA-MRSA in the community.     

Population Structure of a Hybrid Clonal Group of Methicillin-Resistant Staphylococcus aureus,ST239-MRSA-III

The methicillin-resistant Staphylococcus aureus (MRSA) clonal group known as ST239-MRSA-III is notable for its hybrid origin and for causing sustained hospital epidemics worldwide since the late 1970s. We studied the population structure of this MRSA clonal group using a sample of 111 isolates that were collected over 34 years from 29 countries. Genetic variation was assessed using typing methods and novel ascertainment methods, resulting in approximately 15 kb of sequence from 32 loci for all isolates. A single most parsimonious tree, free of homoplasy, partitioned 28 haplotypes into geographically-associated clades, including prominent European, Asian, and South American clades. The rate of evolution was estimated to be approximately 100× faster than standard estimates for bacteria, and dated the most recent common ancestor of these isolates to the mid-20th century. Associations were discovered between the ST239 phylogeny and the ccrB and dru loci of the methicillin resistance genetic element, SCCmec type III, but not with the accessory components of the element that are targeted by multiplex PCR subtyping tools. In summary, the evolutionary history of ST239 can be characterized by rapid clonal diversification that has left strong evidence of geographic and temporal population structure. SCCmec type III has remained linked to the ST239 chromosome during clonal diversification, but it has undergone homoplasious losses of accessory components. These results provide a population genetics framework for the precise identification of emerging ST239 variants, and invite a re-evaluation of the markers used for subtyping SCCmec.     

耐甲氧西林金黄色葡萄球菌染色体盒的研究进展

耐甲氧西林金黄色葡萄球菌（MRSA）的产生是由甲氧西林敏感的金黄色葡萄球菌（MSSA）获得外源性的SCCmec所致。MRSA菌株可以产生一种新的青霉素结合蛋白PBP2a,PBP2a降低了与β-内酰胺类抗生素的亲合力,从而对β-内酰胺类抗生素产生耐药性。PBP2a由mecA基因编码,mecA基因存在于葡萄球菌盒式染色体（Staphylococcal cassette chromosome mec,SCCmec）中,SCCmec是一种可移动的遗传元件,该元件还携带除mecA基因外的其他抗菌药物的耐药基因,造成多重耐药（Multidrug-resistance,MDR）。SCCmec目前主要分为8型,其中又分为若干亚型。SCCmec的基因型与MRSA的流行背景有关,不同地区的SCCmec基因分型分布可能不同。