Characterisation of virulence genes in methicillin susceptible and resistant Staphylococcus aureus isolates from a paediatric population in a university hospital of Medellín, Colombia

Virulence and antibiotic resistance are significant determinants of the types of infections caused by Staphylococcus aureus and paediatric groups remain among the most commonly affected populations. The goal of this study was to characterise virulence genes of methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) strains isolated from a paediatric population of a Colombian University Hospital during 2009. Sixty MSSA and MRSA isolates were obtained from paediatric patients between zero-14 years. We identified the genes encoding virulence factors, which included Panton-Valentine leucocidine (PVL), staphylococcal enterotoxins A-E, exfoliative toxins A and B and toxic shock syndrome toxin 1. Typing of the staphylococcal chromosome cassette mec (SCCmec) was performed in MRSA strains. The virulence genes were more diverse and frequent in MSSA than in MRSA isolates (83% vs. 73%). MRSA strains harboured SCCmec types IVc (60%), I (30%), IVa (7%) and V (3%). SCCmec type IVc isolates frequently carried the PVL encoding genes and harboured virulence determinants resembling susceptible strains while SCCmec type I isolates were often negative. PVL was not exclusive to skin and soft tissue infections. As previously suggested, these differences in the distribution of virulence factor genes may be due to the fitness cost associated with methicillin resistance.     

医院感染葡萄球菌菌种变迁与耐药性近况

目的：了解近9年来医院感染葡萄球菌菌种的变迁与近3年来葡萄球菌药状况。方法：1993年1月至2001年12月我院传染病科等13科室住院病人的各种标本采用血琼脂培养,所分离的葡萄球菌采用美国DADE公司生产的MICROSCAN WALKAY-40全自动微生物分析仪鉴定到种及其亚种。药敏试验药物有青霉素、苯唑西林、氨苄西林、哌拉西林、阿莫西林／克拉维酸（阿莫仙）、头孢唑啉、头孢噻肟、头孢哌酮／舒巴坦（舒普深）、庆大霉素、复方新诺明、环丙沙星、氧氟沙星、利福平、万古霉素、红霉素、林可霉素、四环素、伊米配能／西司他丁（泰能）共18种。采用液体稀释法测定每株葡萄球菌对受试药物的最小抑菌浓度（MIC）,操作按说明书进行。质控菌ATCC25923。依据新近NCCLS标准判读结果。结果：1993年至1998年分离的葡萄球菌中,金黄色葡萄球菌（金葡萄）占71.43%,凝固酶阴性葡萄球菌（CNS）占28.57%,包括表皮葡萄球菌（表葡菌）、腐生葡萄球菌、里昂葡萄球菌和头状葡萄球菌4种。1999年至2001年分离的424株葡萄球菌中,金葡菌仅占29.01%,CNS增至13种,占70.995,以表葡菌、溶血葡萄球菌、松鼠葡萄球菌为主。近3年来分离的各种葡萄球菌甲氧西林耐药率在73.03%-100%之间,除对舒普深、复方新诺明、利福平和万古霉素较敏感外,对其余抗菌药物的耐药率均超过60％,以金葡菌、溶血葡萄球菌、松鼠葡萄球菌的耐药率为最高。MRS耐药率普遍高于MSS,且均呈多重耐药。5.42%(23/424)菌株万古霉素MIC＞16mg/L,除1株为MSCNS外,其余22株均为MRS。结论：3年来医院感染葡萄球菌菌种构成比发生了显著变化,以CNS为主。对抗菌药物呈多重耐药,部分菌株对万古霉素敏感性降低,应予警惕。     

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。     

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.     

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.     

Methicillin resistance in Staphylococcus aureus and coagulase-negative staphylococci: epidemiological and molecular aspects

Infections caused by the genus Staphylococcus are of great importance for human health. Staphylococcus species are divided into coagulase-positive staphylococci, represented by S. aureus, a pathogen that can cause infections of the skin and other organs in immunocompetent patients, and coagulase-negative staphylococci (CNS) which comprise different species normally involved in infectious processes in immunocompromised patients or patients using catheters. Oxacillin has been one of the main drugs used for the treatment of staphylococcal infections; however, a large number of S. aureus and CNS isolates of nosocomial origin are resistant to this drug. Methicillin resistance is encoded by the mecA gene which is inserted in the SCC mec cassette. This cassette is a mobile genetic element consisting of five different types and several subtypes. Oxacillin-resistant strains are detected by phenotypic and genotypic methods. Epidemiologically, methicillin-resistant S. aureus strains can be divided into five large pandemic clones, called Brazilian, Hungarian, Iberian, New York/Japan and Pediatric. The objective of the present review was to discuss aspects of resistance, epidemiology, genetics and detection of oxacillin resistance in Staphylococcus spp., since these microorganisms are increasingly more frequent in Brazil.     

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。     

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.     

Staphylococci in orthopaedic surgical wounds.

From 50 infected surgical wounds of orthopaedic patients, 43 (86%) staphylococcal strains were isolated. 34 of all these staphylococci belonged to Staphylococcus aureus species (i.e. 68 % of all isolates from surgical wounds; 79% of staphylococcal isolates); 9 were coagulase-negative staphylococci (i.e. 21% of all isolates from surgical wounds; 18% of staphylococcal isolates). Among microorganisms isolated from the wounds we also found 2 (4%) of the Enterobacteriaceae family; 2 (4%) of the Pseudomonas genus; 3 (6%) of the Streptococcus genus. Thus, orthopaedic surgical wounds were infected by staphylococci (mainly S. aureus) more frequently than by other micro-organisms. All the staphylococcal strains were screened for methicillin resistance by agar disk diffusion testing and for the presence of mecA gene responsible for methicillin resistance by PCR. 32% of the S. aureus and 33% of the S. epidermidis strains resulted methicillin resistant and mecA-positive. The data confirm the diffusion of methicillin resistant S. aureus in surgical site infections and shows that the so-called "new pathogens", i.e. S. epidermidis and other coagulase-negative staphylococci, also exhibit a frequent and hazardous methicillin-resisting ability.     

Bacteriocins as alternative agents for control of multiresistant staphylococcal strains

AIMS: To investigate the activity of seven staphylococcins, bacteriocins produced by staphylococci, against multiresistant Staphylococcus aureus and coagulase-negative staphylococci (CNS) involved in human infections. METHODS AND RESULTS: Four bacteriocins produced by Staph. epidermidis (Pep5, epidermin, epilancin K7 and epicidin 280) and three produced by Staph. aureus (aureocins A70, A53 and 215FN) were tested. Sixteen Staph. aureus strains, including a representative strain of the endemic Brazilian methicillin-resistant clone (MRSA), and 57 CNS strains were used as indicators. Among the staphylococcins used, Pep5 was able to inhibit 77.2% of the CNS strains and 87.5% of the Staph. aureus strains tested, including the Brazilian MRSA endemic clone, responsible for a large number of hospital-acquired infections in Brazil. On the other hand, aureocin A53 and epidermin presented a high antagonistic activity only against the Staph. aureus strains, being able to inhibit, respectively, 87.5% and 81.3% of them, including also the Brazilian MRSA endemic clone. The remaining bacteriocins inhibited only a low percentage of the nosocomial staphylococcal strains tested. CONCLUSIONS: Aureocin A53 and epidermin have potential applications against MRSA, whereas Pep5 seems to be an attractive agent against both MRSA and CNS, including mupirocin-resistant strains and the Brazilian endemic clone of MRSA, which is also found disseminated in other countries. SIGNIFICANCE AND IMPACT OF THE STUDY: Bacteriocins may represent alternative agents to control important nosocomial pathogens.     

MRSA的7种新SCCmec型别及其抗药特性

为探明海口地区耐甲氧西林金黄色葡萄球菌(MRSA)的耐药性和携带的葡萄球菌染色体mec盒(SCCmec)型别,对收集的1174株金黄色葡萄球菌用PBP2a检测法确证为MRSA有686株,用多重PCR对58株进行SCCmec分型测定,并用K-B琼脂扩散法和E-test法测定其对临床常用7类抗生素的代表性药物耐药性。结果在17株中又发现了7种新的SCCmec型别,其结构特点为:New3含A、F、H、M4个位点,New4型含F、H、M3个位点,New5含D、B、M3个位点,New6型含A、B、M3个位点,New7型含H、E、C、M4个位点,New8型含A、M两个位点,New9型含A、C、M3个位点;它们均与报道型别的结构特点存在明显差异;且携带新型的MRSA菌株,其分布特点及抗药性也与已报道的菌株存在差异:多分自门诊病人,且耐药性高,抗药谱较广,值得引起高度重视和关注。     

MRSA的7种新SCCmec型别及其抗药特性

为探明海口地区耐甲氧西林金黄色葡萄球菌(MRSA)的耐药性和携带的葡萄球菌染色体mec盒(SCCmec)型别,对收集的1174株金黄色葡萄球菌用PBP2a检测法确证为MRSA有686株,用多重PCR对58株进行SCCmec分型测定,并用K-B琼脂扩散法和E-test法测定其对临床常用7类抗生素的代表性药物耐药性。结果在17株中又发现了7种新的SCCmec型别,其结构特点为:New3含A、F、H、M4个位点,New4型含F、H、M3个位点,New5含D、B、M3个位点,New6型含A、B、M3个位点,New7型含H、E、C、M4个位点,New8型含A、M两个位点,New9型含A、C、M3个位点;它们均与报道型别的结构特点存在明显差异;且携带新型的MRSA菌株,其分布特点及抗药性也与已报道的菌株存在差异:多分自门诊病人,且耐药性高,抗药谱较广,值得引起高度重视和关注。     

Enterotoxigenicity of Staphylococcus aureus Cultures Isolated from Acute Cases of Bovine Mastitis

To determine whether staphylococci causing bovine mastitis are potential causes of human intoxications, 142 cultures identified as etiological agents of acute cases and 18 cultures causing chronic cases of staphylococcal mastitis were obtained from investigators in the United States and Canada, examined microscopically, and tested for carbohydrate utilization, terminal pH, catalase, coagulase, egg yolk hydrolysis, gelatin hydrolysis, cytochrome oxidase, urease production, nitrate reduction, micrococcal nuclease, phage type, and enterotoxin production. Three cultures were not confirmed as Staphylococcus aureus. Of the 157 S. aureus cultures, 23 produced staphylococcal enterotoxins. Although a direct relationship between staphylococcal mastitis and outbreaks of staphylococcal food poisoning was not proved, results indicated that staphylococcal infections of the bovine mammary gland represent a significant reservoir of enterotoxigenic strains of S. aureus.     

Prospective surveillance of community-onset and healthcare-associated methicillin-resistant Staphylococcus aureus isolated from a university-affiliated hospital in Japan

We conducted a prospective comparative study of community-onset (CO) and healthcare-associated (HA) methicillin-resistant Staphylococcus aureus(MRSA) strains between 2000 and 2001 at Tokyo Women's Medical University Hospital (1,500 beds) in Japan. Of the 172 consecutive MRSA isolates analyzed, 13 (8%) were categorized as CO-MRSA. The mean age of patients with CO-MRSA was significantly younger than that of patients with HA-MRSA. Most CO-MRSA strains were isolated from skin and more likely to be susceptible to erythromycin, clindamycin, tetracycline, levofloxacin, and spectinomycin compared to HA-MRSA isolates. Pulsed-field gel electrophoresis (PFGE) analysis, staphylococcal cassette chromosome mec(SCCmec) typing, and multi-locus sequence typing (MLST) revealed that CO-MRSA strains were divided into the following multi-clones: 3 clone A: II: ST5 (PFGE type: SCCmec type: MLST sequence type); 1 L: II: ST5; 1 H: IV: ST1; 1 I: IV: ST81; 2 D: IV: ST8; 1 B: IV: ST89; 1 B: IV: ST379; and 3 B: IV: ST91. Of the 159 HAMRSA strains, 124 (78%) belonged to a single clone (PFGE clone A: SCCmec type II: tst and sec positive: coagulase type II: multi-drug resistance). Four CO-MRSA strains belonging to PFGE clone B: SCCmec type IV: MLST clonal complex 509 (ST89, 91, 379) had the exfoliative toxin B (etb) genes, but all CO-MRSA and HA-MRSA strains did not possess the Panton-Valentine leukocidin (pvl) genes. These results demonstrate that multiple lineages of CO-MRSA have the potential for dissemination in the community in Japan.     

金黄色葡萄球菌儿童临床分离株携带PVL基因状况的分析

目的了解金黄色葡萄球菌儿童分离株携带Panton-Valentine杀白细胞素（PVL）基因的状况及感染类型。方法采用多重PCR同时检测金黄色葡萄球菌16SrRNA基因、PVL基因和mecA基因;多重PCR检测MR—SA的SCCmec基因型及亚型。结果66株金黄色葡萄球菌JL童临床分离株经多重PCR检测,其中MRSA有7株（10．6％）,MSSA有59株（89．4％）;携带PVL基因金黄色葡萄球菌有31株,总阳性率为47．O％（31／66）,其中2株为MRSA,29株为MSSA,阳性率分别为28．6％（2／7）和49。2％（29／59）。2株MRSA都属于SCCmecIV型;31株PVL基因阳性分离株有21株分离自脓液,7株分离自血液,仅1株分离自痰液。结论儿童MSSA是携带PVL基因的主要菌株,携带PVL基因的金黄色葡萄球菌主要引起化脓性感染和血流感染。     

Multiple-locus variable number of tandem repeats fingerprinting (MLVF) and virulence factor analysis of methicillin resistant Staphylococcus aureus SCCmec type III

Methicillin resistant Staphylococcus aureus (MRSA), particularly strains with type III staphylococcal cassette chromosome mec (SCCmec), represent a serious human pathogen in Tehran, Iran. The disease-causing capability depends on their ability to produce a wide variety of virulent factors. The prevalence of exotoxin genes and multiple-locus variable number of tandem repeats fingerprinting (MLVF) profile among MRSA isolates, from patients in Tehran, was evaluated by PCR and Multiplex-PCR. The MLVF typing of 144 MRSA isolates with type III SCCmec produced 5 different MLVF types. Generally, 97.2% (140/144) of all the isolates were positive for at least one of the tested exotoxin genes. The most prevalent genes were hld, found in 87.5% (126/144) of the isolates followed by lukE-lukD and hla found in 72.9% (105/144) and 70.1% (101/144) of the isolates, respectively. The tst gene, belonging to MLVF types I, IV and V, was found among three of the isolates from blood and wound samples. The sea gene was detected in 58.3% (84/144) of the isolates and the sed and see genes were found in one isolate with MLVF type V. The coexistence of genes was observed in the 87.5% (126/144) of the isolates. The rate of coexistence of hld with lukE-lukD, hla with lukE-lukD and sea with lukE-lukD were 66.7% (96/144), 44.4% (64/144) and 44.4% (64/144), respectively. The present study demonstrated that MRSA strains with type III SCCmec show different MLVF patterns and exotoxin profiles.     

Potential of the polyvalent anti-Staphylococcus bacteriophage K for control of antibiotic-resistant staphylococci from hospitals

The increasing prevalence of antibiotic-resistant staphylococci has prompted the need for antibacterial controls other than antibiotics. In this study, a lytic bacteriophage (phage K) was assessed in vitro for its ability to inhibit emerging drug-resistant Staphylococcus aureus strains from hospitals and other species of Staphylococcus isolated from bovine infections. In in vitro inhibitory assays, phage K lysed a range of clinically isolated methicillin-resistant S. aureus (MRSA) strains, S. aureus with heterogeneous vancomycin resistance and vancomycin resistance, and teicoplanin-resistant strains. In these assays, 14 of the MRSA strains were initially only weakly sensitive to this phage. However, propagation of phage K on these less-sensitive strains resulted in all 14 being sensitive to the modified phages. The results enforce the principle that, while certain target bacteria may be relatively insensitive to lytic phage, this can be overcome by obtaining modified phage variants from passage of the phage through the insensitive strains. Model in situ hand wash studies using a phage-enriched wash solution resulted in a 100-fold reduction in staphylococcal numbers on human skin by comparison with numbers remaining after washing in phage-free solution. Infusion of the phage into a nonimmunogenic bismuth-based cream resulted in strong anti-Staphylococcus activity from the cream on plates and in broth.     

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 SCCmec typing. Thirty strains had the class 1 integrase (intI1) gene and 26 strains possessed the 3' conserved region of qacEDelta1-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 SCCmec typing for 30 integron-bearing MRCNS strains, five, 15 and five strains belonged to type I, II and III SCCmec, 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 SCCmec, 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.     

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     

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.