耐甲氧西林金黄色葡萄球菌分型及流行现状

【目的】研究杭州地区耐甲氧西林金黄色葡萄球菌(Methicillin-resistant Staphylococcus aureus,MRSA)的基因型别,探讨MRSA菌株流行变化趋势及进化特点,为该地区MRSA的进一步防治提供科学依据。【方法】对86株MRSA进行葡萄球菌盒式染色体SCCmec基因、spa基因分型,并开展多位点序列分型(Multi-locus sequence typing,MLST),与国际上MRSA的流行型别进行比较,分析进化关系。【结果】86株MRSA共发现13个spa型(以t311型为主,占48.8%;其次为t6418型,占11.6%);MLST分型共发现9个ST型(以ST5为主,占59.3%;其次为ST239,占16.3%),经e BURST软件分析它们属于4个群(Group 1、Group 6、Group 8、Group 12)和8种克隆复合体(CC1、CC5、CC630、CC20、CC59、CC88、CC239、CC573);SCCmec基因分型以SCCmecⅡ型为主,占61.6%;其次为SCCmec III型,占22%;5株社区相关性MRSA(SCCmec-Ⅳ型)。其中第一流行克隆型为SCCmec-Ⅱ-ST5-t311-CC5(占47.7%)、其次为SCCmec-III-ST239-t030/t037-CC239(占12.8%)。【结论】SCCmec-Ⅱ-ST5-t311为杭州地区当前流行菌株;CA-MRSA菌株的出现,提示MRSA菌株有由医院向社区播散的趋势;此外,对新发展了单位点变体的菌株(SCCmec-Ⅰ-ST1921-t164-CC20和SCCmec-Ⅳ-ST965-t062-CC5),应加强重视。     

SCCmec in staphylococci: genes on the move

Staphylococcal cassette chromosome (SCC) elements are, so far, the only vectors described for the mecA gene encoding methicillin resistance in staphylococci. SCCmec elements are classified according to the type of recombinase they carry and their general genetic composition. SCCmec types I-V have been described, and SCC elements lacking mecA have also been reported. In this review, we summarize the current knowledge about SCC structure and distribution, including genetic variants and rudiments of the elements. Its origin is still unknown, but one assumes that staphylococcal cassette chromosome is transferred between staphylococci, and mecA-positive coagulase-negative staphylococci may be a potential reservoir for these elements. Staphylococcal genomes seem to change continuously as genetic elements move in and out, but no mechanism of transfer has been found responsible for moving SCC elements between different staphylococcal species. Observations suggesting de novo production of methicillin-resistant staphylococci and horizontal gene transfer of SCCmec will be discussed.     

Methicillin-resistant Staphylococcus pseudintermedius isolated from canine pyoderma in North China

Aims: To determine the prevalence of carriage of methicillin‐resistant Staphylococcus pseudintermedius (MRSP) among dogs with pyoderma from two small animal hospitals in North China during a 21‐month period and to characterize these isolates. Methods and Results: Swabs were taken from 260 dogs with pyoderma, and the staphylococcal species isolated and methicillin resistance were confirmed phenotypically and genotypically. The identified MRSP isolates were characterized by multilocus sequence typing (MLST), spa typing, staphylococcal cassette chromosome (SCC) mec typing, testing for susceptibility to nine antimicrobial agents and SmaI‐digested pulsed‐field gel electrophoresis. Thirty‐three (12·7%) dogs were positive for MRSP. The most prevalent genotypes detected among MRSP were ST71(MLST)‐t06(spa)‐II‐III(SCCmec) (n = 22, 66·7%), followed by ST5‐t19 (n = 8, 24·2%), ST126‐III(n = 2, 6·1%) and ST6‐t02‐V (3·0%). All MRSP isolates showed extended resistance to tested antimicrobial agents. Eight different SmaI patterns were observed in 21 typeable MRSP isolates. Conclusions: Clinical isolates of MSRP isolated from dogs in North China belonged to two major clonal lineages ST71 and ST5. Significance and Impact of the Study: This study is the first report on MRSP from canine pyoderma in China. Further surveillance study is needed to gain more detailed data concerning this major clinical challenge in veterinary medicine.     

New categories designated as healthcare‐associated and community‐associated methicillin‐resistant Staphylococcus pseudintermedius in dogs

The incidence of MRSP has been increasing, and treatment options in veterinary medicine are limited. Few previous studies of MRSP have described the relationships between the genotypes, phenotypes, and clinical backgrounds of the isolates. To gain insight into the associations between the microbiological and clinical characteristics of MRSP, we analyzed 282 Staphylococcus pseudintermedius isolates from dogs. A total of 195 (69.1%) strains were identified as mecA‐positive MRSP and were classified into mainly two genotypes: SCCmec types III (II‐III) (52.8%) and V (37.4%). SCCmec type III MRSP strains were significantly correlated with hospital admission and antimicrobial therapy of the dogs, and exhibited a homogeneous genotype similar to sequence type 71‐MRSP, which is a globally endemic clone in dogs. In contrast, SCCmec type V MRSP strains were not highly correlated with hospital admission and antimicrobial therapy and exhibited genotypic and phenotypic heterogeneity. Properties of MRSP strains SCCmec types III and V were similar to those of HA‐ and CA‐MRSA, respectively. Therefore, we designated these isolates carrying SCCmec types III and V as HA‐MRSP and CA‐MRSP, respectively. Discrimination between HA‐ and CA‐MRSP by oxacillin MIC will provide useful information for treatment and infection control measures for canine MRSP infections.     

耐甲氧西林金黄色葡萄球菌分子分型研究进展

近年来,耐甲氧西林金黄色葡萄球菌在全世界各地感染率和分离率不断提高,已成为目前院内感染的重要病原菌之一。运用有效、可靠、廉价的分子分型方法对分析耐甲氧西林金黄色葡萄球菌的流行病学特征及来源,对制定控制院感及流行的措施非常重要的。本研究概述了各种分子分型方法的原理及比较,如SCCmec分型、脉冲场凝胶电泳分型、多位点序列分型、葡萄球菌A蛋白分型和毒力因子分型等。脉冲场凝胶电泳仍然是暴发流行中MRSA分子分型的金标准,而其他分型方法更适合用于检测菌株的变异和建立国际监测。     

临床分离耐甲氧西林溶血性葡萄球菌的SCCmec分型及同源性分析

目的了解临床分离耐甲氧西林溶血性葡萄球菌（MRSH）的SCCmec基因型别及相同SCCmec型别菌株的同源性。方法多重PCR进行SCCmec分型,ERIC-PCR法对相同SCCmec型别菌株进行同源性分析。结果83株临床分离MRSH菌株中,SCCmecI型有23株（27．7％）,SCCmecⅡ型有10株（12．1％）,SCCmecm型有24株（28．9％）,SCCmecIV型有1株（1．2％）,I、Ⅱ混合型有8株（9．6％）,I、Ⅲ混合型有6株（7．2％）,Ⅱ、11混合型有5株（6．0％）,I、Ⅱ、Ⅲ混合型有3株（3．6％）,未分型3株（3．6％）。ERIC—PCR结果显示,23株SCCmecI型分为11型,其中A型5株,B型5株,C型3株,其余8株各为1型,2株未分型;10株SCCmecⅡ型分为6型,其中D型4株,E型2株,3株各为1型,1株未分型;24株SCCmecm型分为9型,其中F型11株,G型2株,H型2株,I型2株,5株各为1型,2株未分型。结论临床分离MRSH中,SCCmecI、Ⅲ型为多,部分菌株呈混合型别;相同SCCmec型别的部分菌株之间可能存在克隆传播。     

An evaluation of survival and detection of Campylobacter jejuni and C. coli in broiler caecal contents using culture‐based methods

Aims: (i) To cultivate methicillin‐resistant Staphylococcus aureus (MRSA) from a full‐scale wastewater treatment plant (WWTP), (ii) To characterize the indigenous MRSA‐flora, (iii) To investigate how the treatment process affects clonal distribution and (iv) To examine the genetic relation between MRSA from wastewater and clinical MRSA. Methods: Wastewater samples were collected during 2 months at four key sites in the WWTP. MRSA isolates were characterized using spa typing, antibiograms, SSCmec typing and detection of Panton–Valentine leukocidin (PVL). Conclusions: MRSA could be isolated on all sampling occasions, but only from inlet and activated sludge. The number of isolates and diversity of MRSA were reduced by the treatment process, but there are indications that the process was selected for strains with more extensive antibiotic resistance and PVL+ strains. The wastewater MRSA‐flora had a close genetic relationship to clinical isolates, most likely reflecting carriage in the community. Significance and Impact of the Study: This study shows that MRSA survives in wastewater and that the WWTP may be a potential reservoir for MRSA.     

Multiplex PCR Assay for Typing of Staphylococcal Cassette Chromosome Mec Types I to V in Methicillin-resistant Staphylococcus aureus

Staphylococcal Cassette Chromosome mec (SCCmec)typing is a very important molecular tool for understanding the epidemiology and clonal strain relatedness of methicillin-resistant Staphylococcus aureus (MRSA), particularly with the emerging outbreaks of community-associated MRSA (CA-MRSA) occurring on a worldwide basis. Traditional PCR typing schemes classify SCCmec by targeting and identifying the individual mec and ccr gene complex types, but require the use of many primer sets and multiple individual PCR experiments. We designed and published a simple multiplex PCR assay for quick-screening of major SCCmec types and subtypes I to V, and later updated it as new sequence information became available. This simple assay targets individual SCCmec types in a single reaction, is easy to interpret and has been extensively used worldwide. However, due to the sophisticated nature of the assay and the large number of primers present in the reaction, there is the potential for difficulties while adapting this assay to individual laboratories. To facilitate the process of establishing a MRSA SCCmec assay, here we demonstrate how to set up our multiplex PCR assay, and discuss some of the vital steps and procedural nuances that make it successful.     

Characterization of MLS(b) resistance among Staphylococcus aureus and Staphylococcus epidermidis isolates carrying different SCCmec types

This work characterizes MLS(b) resistance in 39 methicillin-resistant Staphylococcus aureus (MRSA) and 32 Staphylococcus epidermidis (MRSE) isolates. Of 21 erm(A) gene encoding MRSA isolates, 71.4% carried SCCmecIII, whereas of 12 isolates carrying the erm(C) gene, 83.3% carried SCCmecIV. Among the 25 MRSE isolates positive for the erm(C) gene, 80% had SCCmecIV or nontypeable cassettes. Isolates carrying these genes had MIC(90) ≥ 256 μg/mL to erythromycin and clindamycin. The msr(A) gene was associated with a low MIC(90) to these drugs. The erm(A) gene was associated with SCCmecIII in MRSA isolates, whereas the erm(C) gene was associated with SCCmecIV in both MRSA and MRSE isolates.     

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。