Novel type of staphylococcal cassette chromosome mec identified in community-acquired methicillin-resistant Staphylococcus aureus strains

We identified a new type of staphylococcal cassette chromosome mec (SCCmec) from two community-acquired methicillin-resistant Staphylococcus aureus (MRSA) strains. The novel element, designated type IV SCCmec, had a unique combination of the class B mec gene complex and the type 2 ccr gene complex and was much smaller in size (21 to 24 kb) than previously identified SCCmec elements of hospital-acquired MRSA. Consistent with the strains' susceptibilities to various non-beta-lactam antibiotics, the type IV SCCmec was devoid of any antibiotic resistance genes other than the mecA gene.     

Novel type of staphylococcal cassette chromosome mec in a methicillin-resistant Staphylococcus aureus strain isolated in Sweden

We identified a novel type of staphylococcal cassette chromosome mec (SCCmec) element carried by methicillin-resistant Staphylococcus aureus (MRSA) strain JCSC6082 isolated in Sweden. The SCCmec element was demarcated by characteristic nucleotide sequences at both ends and was integrated at the 3' end of orfX. The element carried a novel combination of a type 5 ccr gene complex and class C1 mec gene complex. The J regions of the element were homologous to those of the SCCmercury element of S. aureus strain 85/2082, with nucleotide identity greater than 99%. However, the novel SCCmec element from JCSC6082 did not carry the mer operon nor Tn554, suggesting that evolution to SCCmec could have been from a common ancestor by acquisition of the class C1 mec gene complex. The novel SCCmec element from JCSC6082 was flanked by a novel SCC-like chromosome cassette (CC6082), which was demarcated by two direct repeats and could be excised from the chromosome independently of the SCCmec element. Our data suggest that novel SCCmec elements can be generated on the staphylococcal chromosome through the recombination between extant SCC elements and mec gene complexes.     

Novel types of staphylococcal cassette chromosome mec elements identified in clonal complex 398 methicillin-resistant Staphylococcus aureus strains

The structures of staphylococcal cassette chromosome mec (SCCmec) elements carried by 31 clonal complex 398 (CC398) methicillin-resistant Staphylococcus aureus (MRSA) strains isolated from the participants at a conference were analyzed. The SCCmecs were classified into novel types, namely, IX, X, V(5C2&5) subtype c, and IVa. Type V(5C2&5) subtype c, IX, and X SCCmecs carried genes conferring resistance to metals. The structures of SCCmecs from CC398 strains were distinct from those normally found in humans, adding to the evidence that humans are not the original host for CC398.     

Superantigenic toxin genes coexist with specific staphylococcal cassette chromosome mec genes in methicillin-resistant Staphylococcus aureus

Staphylococcus aureus is a leading cause of human disease in the hospital setting and the community. Superantigenic toxin-producing methicillin-resistant Staphylococcus aureus (MRSA) is currently important for nosocomial infections and food-borne diseases worldwide because of its global spreading and difficulty in therapy. Superantigenic toxins can bypass normal antigen presentation and have strong T cell mitogenic activity, leading to massive release of proinflammatory cytokines and contributing to the severity of S. aureus sepsis. In this study, a total of 131 MRSA isolates from patients in the University Hospital were searched for staphylococcal cassette chromosome mec (SCCmec) genes and the staphylococcal superantigenic toxin genes by multiplex polymerase chain reactions. The MRSA isolates were classified into SCCmec type II (74.8%), type I (13.0%), type IV (3.8%), type V (2.3%), and type I and type II (3.8%). MRSA isolates (102/131) also carried a number of superantigenic toxin genes including staphylococcal enterotoxin (se) and toxic shock syndrome toxin-1 (tst-1) genes. The most frequent superantigen gene profile (55/131, 42.0%) of the MRSA isolates includes staphylococcal enterotoxin C (sec), seg, sei, staphylococcal enterotoxin-like L (sell), selm, seln, selo, and tst-1. Furthermore, SCCmec type I or type II MRSA isolates more frequently harbor sec, seg, sei, sell, selm, seln, selo, and tst-1 genes, compared to other types of MRSA. These results indicate that the selected superantigenic toxin genes are linked to SCCmec type I and type II. The coexistence of these toxins and the SCCmec genes in S. aureus may contribute to the biological fitness and pathogenicity of MRSA.     

Novel and uncommon antimicrobial resistance genes in livestock-associated methicillin-resistant Staphylococcus aureus

Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) isolates have been the subject of numerous studies during recent years. The characterization of such isolates has usually also included the determination of their resistance phenotypes and associated resistance genotypes. Analysis of the resistance genes present in LA-MRSA isolates has revealed a number of genes commonly found in S. aureus and coagulase-negative staphylococci of humans and animals. In addition, novel resistance genes and/or resistance genes that have been rarely detected in staphylococci so far have been encountered. These include the phenicol exporter gene fexA, the multiresistance gene cfr, the tetracycline resistance gene tet(L), the trimethoprim resistance gene dfrK, the macrolide-lincosamide-streptogramin B resistance gene erm(T), the lincosamide-streptogramin A-pleuromutilin resistance genes vga(C) and vga(E), and the apramycin resistance gene apmA. Most of these genes were located on multiresistance plasmids in LA-MRSA. The co-localization of these resistance genes with other resistance genes enables their co-selection and persistence. LA-MRSA can therefore act as a donor and a recipient of antimicrobial resistance genes within the Gram-positive gene pool.     

耐甲氧西林金黄色葡萄球菌mec Ⅰ基因的检测及多态性研究

目的研究耐甲氧西林金黄色葡萄球菌（methieillin-resistant Staphylococcus aureus，MRSA）临床分离株mecⅠ基因多态性。方法随机挑取我2005年1月至2006年8月间40株经PCR检测mecA阳性的金黄色葡萄球菌，采用PCR检测mecⅠ基因，对PCR产物进行测序。多重PCR检测葡萄球菌盒式染色体（Staphylococcal cassette chromosome mec，SCCmec），使用琼脂稀释法检测苯唑西林的MIC值。结果40株MRSA中有35株mecⅠ基因阳性，阳性率为87．5％（35／40），所有35株mecⅠ基因阳性的菌株都存在mecⅠ202位C→T点突变，导致68位的谷氨酰胺的密码子CAA变成终止密码子UAA。32株菌为mecⅠ202单点突变，3株菌存在两位点突变，分别为3位插入A，41位A→C，142位C→T。35株mecⅠ阳性菌株中，有27株SCCmec为SCCmecⅢ、7株为SCCmecⅢA及1株SCCmec Ⅱ，5株mecⅠ阴性的菌株中，3株为SCCmecⅣ，1株为SCCmecⅠ，另1株为未知型。31株mecⅠ202单点突变菌株对苯唑西林（Oxacillin，OXA）的MIC值在256～512μg／ml，1株mecⅠ202单点突变菌株的MIC值〈1μg／ml，3株存在两个位点突变的菌株对苯唑西林的MIC值≥512μg／ml，5株mecⅠ阴性的菌株对苯唑西林的MIC值在8～256μg／ml之间。结论本地区分离的MRSA临床分离株普遍存在mecⅠ202C→T，少数菌株mecⅠ202和其他位点同时存在突变，mecⅠ202位点突变是MRSA对苯唑西林高水平耐药的主要原因。     

Seven novel variants of the staphylococcal chromosomal cassette mec in methicillin-resistant Staphylococcus aureus isolates from Ireland

Methicillin-resistant Staphylococcus aureus (MRSA) isolates recovered in Irish hospitals between 1971 and 2002 were characterized using multilocus sequence typing (MLST) (n = 130) and SCCmec typing (n = 172). Where atypical SCCmec typing results were obtained, PCR amplification of entire SCCmec elements, analysis of amplimer mobility, and nucleotide sequencing were undertaken. MLST revealed that 129/130 isolates had the same genotypes as internationally spread MRSA clones, including ST239, ST247, ST250, ST5, ST22, ST36, and ST8. A novel genotype, ST496, was identified in one isolate. Half of the isolates (86/172) had SCCmec type I, IA, II, III, or IV. The remaining 86 isolates harbored novel SCCmec variants in three distinct genetic backgrounds: (i) 74/86 had genotype ST8 and either one of five novel SCCmec II (IIA, IIB, IIC, IID, and IIE) or one of two novel SCCmec IV (IVE and IVF) variants; (ii) 3/86 had genotype ST239 and a novel SCCmec III variant; (iii) 9/86 had a novel SCCmec I variant associated with ST250. SCCmec IVE and IVF were similar to SCCmec IVc and IVb, respectively, but differed in the region downstream of mecA. The five SCCmec II variants were similar to SCCmec IVb in the region upstream of the ccr complex but otherwise were similar to SCCmec II, except for the following regions: SCCmec IIA and IID had a novel mec complex, A.4 (Delta mecI-IS1182-Delta mecI-mecR1-mecA-IS431mec); SCCmec IIC and IIE had a novel mec complex, A.3 (IS1182-Delta mecI-mecR1-mecA-IS431mec); SCCmec IID and IIE lacked pUB110; SCCmec IIC and IIE lacked a region of DNA between Tn554 and the mec complex; and SCCmec IIB lacked Tn554. This study has demonstrated a hitherto-undescribed degree of diversity within SCCmec.     

医院感染甲氧西林耐药金黄色葡萄球菌的SCCmec分型及同源性研究

目的研究多重耐药的甲氧西林耐药金葡菌（MRSA）菌株的SCCmec基因分型,并对菌株进行同源性分析。方法纳入26株耐药谱相同的MRSA菌株,采用多重PCR检测SCCmec的分型;应用Rep-PCR法采用DiversiLb系统对菌株进行同源性分析。结果 26株MRSA的SCmec多数为Ⅲ型,占84.6%,另检出Ⅱ型2株、Ⅳ型1株,1株未能分型;未发现I型SCCmec。DiversiLab分析结果显示MRSA可分为10组,同源性介于40%～100%。其中SCCmee-Ⅱ亚型2株完全相同。SCCmec-Ⅲ亚型subtype 1型相似性在90%以上;subtype 3型4株为同一组、MRSA相似性在95%以上;subtype 2型可分为5组,相似性在90%以上。结论医院感染多重耐药的MRSA多数以SCCmec-Ⅲ型为主,医院内存在一定流行,应引起临床医师及感染控制部门重视。     

金黄色葡萄球菌的药敏表型和耐甲氧西林金黄色葡萄球菌的SCCmec基因分型

目的研究从临床标本中分离的金黄色葡萄球菌（SA）的耐药性、耐甲氧西林金黄色葡萄球菌（MRSA）的发生率及其葡萄球菌盒式染体色mec（SCCmec）基因分型。方法采用纸片琼脂扩散法进行SA耐药性检测及MRSA测定,应用多重聚合酶链反应（PCR）进行SCCmec各基因型及PV杀白细胞素（PVL）基因型的检测。结果 102株SA中检出39株MRSA,检出率为38.2%（39/102）。甲氧西林敏感金黄色葡萄球菌（MSSA）对克林霉素、复方磺胺甲口恶唑、四环素3种抗菌药物耐药率较高,分别为39.7%、31.7%、22.2%;对庆大霉素及喹诺酮类耐药率较低,为6.3%~14.3%。而MRSA对克林霉素、β-内酰胺类抗菌药物100%耐药,对其他药物表现为多重耐药。未检出万古霉素耐药菌株。MRSA菌株的SCCmec基因型以SCCmecⅢ型为主,占71.2%,SCCmecⅣa占10.3%,未检测出PVL基因。结论临床分离的SA中,MRSA耐药率较MSSA高且表现为多重耐药,其SCCmec基因分型主要表现为SCCmecⅢ型,其次是SCCmecⅣa。     

金黄色葡萄球菌的药敏表型和耐甲氧西林金黄色葡萄球菌的SCCmec基因分型

目的研究从临床标本中分离的金黄色葡萄球菌(SA)的耐药性、耐甲氧西林金黄色葡萄球菌(MRSA)的发生率及其葡萄球菌盒式染体色mec(SCCmec)基因分型。方法采用纸片琼脂扩散法进行SA耐药性检测及MRSA测定,应用多重聚合酶链反应(PCR)进行SCCmec各基因型及PV杀白细胞素(PVL)基因型的检测。结果 102株SA中检出39株MRSA,检出率为38.2%(39/102)。甲氧西林敏感金黄色葡萄球菌(MSSA)对克林霉素、复方磺胺甲口恶唑、四环素3种抗菌药物耐药率较高,分别为39.7%、31.7%、22.2%;对庆大霉素及喹诺酮类耐药率较低,为6.3%~14.3%。而MRSA对克林霉素、β-内酰胺类抗菌药物100%耐药,对其他药物表现为多重耐药。未检出万古霉素耐药菌株。MRSA菌株的SCCmec基因型以SCCmecⅢ型为主,占71.2%,SCCmecⅣa占10.3%,未检测出PVL基因。结论临床分离的SA中,MRSA耐药率较MSSA高且表现为多重耐药,其SCCmec基因分型主要表现为SCCmecⅢ型,其次是SCCmecⅣa。     

Detection of staphylococcal cassette chromosome mec type XI carrying highly divergent mecA, mecI, mecR1, blaZ, and ccr genes in human clinical isolates of clonal complex 130 methicillin-resistant Staphylococcus aureus

Methicillin resistance in staphylococci is mediated by penicillin binding protein 2a (PBP 2a), encoded by mecA on mobile staphylococcal cassette chromosome mec (SCCmec) elements. In this study, two clonal complex 130 (CC130) methicillin-resistant Staphylococcus aureus (MRSA) isolates from patients in Irish hospitals were identified that were phenotypically PBP 2a positive but lacked mecA by conventional PCR and by DNA microarray screening. The isolates were identified as methicillin-susceptible S. aureus using the GeneXpert real-time PCR assay. Whole-genome sequencing of one isolate (M10/0061) revealed a 30-kb SCCmec element encoding a class E mec complex with highly divergent blaZ-mecA-mecR1-mecI, a type 8 cassette chromosome recombinase (ccr) complex consisting of ccrA1-ccrB3, an arsenic resistance operon, and flanking direct repeats (DRs). The SCCmec element was almost identical to that of SCCmec type XI (SCCmec XI) identified by the Sanger Institute in sequence type 425 bovine MRSA strain LGA251 listed on the website of the International Working Group on the Classification of Staphylococcal Cassette Chromosome Elements. The open reading frames (ORFs) identified within SCCmec XI of M10/0061 exhibited 21 to 93% amino acid identity to ORFs in GenBank. A third DR was identified ca. 3 kb downstream of SCCmec XI, indicating the presence of a possible SCC remnant. SCCmec XI was also identified in the second CC130 MRSA isolate by PCR and sequencing. The CC130 MRSA isolates may be of animal origin as previously reported CC130 S. aureus strains were predominantly from bovine sources. The highly divergent nature of SCCmec XI relative to other SCCmec elements indicates that it may have originated in another taxon.     

天津地区耐甲氧西林金黄色葡萄球菌基因分型研究

MRSA已成为引起感染的主要病原菌,可导致各种感染.但是近年来MRSA出现了快速的进化演变,其感染不仅限于医院感染,且开始出现在社区感染中,称之为社区获得性MRSA(CA-MRSA).它的不断出现以及所引起的致死性疾病严重威胁人类健康.目前MRSA耐药严重,呈多重耐药性,特别是近年来出现万古霉素中介(VISA)或耐药(VRSA)的金黄色葡萄球菌,MRSA的感染已成为伞球公共卫生问题之一.因此,掌握MRSA的分子特征对于有效控制感染及鉴别菌株的相关性十分重要.为此本研究采用葡萄球菌盒式基因(SCCmec)多重PCR分型技术和多位点序列分型(MLST)技术,对天津地区4所医院分离出的104株MRSA菌株进行基因分型研究,以了解这些菌株的基因分型特征.     

Novel mobile variants of staphylococcal cassette chromosome mec in Staphylococcus aureus

Staphylococcus aureus staphylococcal cassette chromosome mec type IV (SSCmec IV) is associated with virulent community-acquired methicillin-resistant Staphylococcus aureus (MRSA) and frequent horizontal transfer among staphylococci. To gain insight into the mechanism of transfer, we studied the ccrA/B type 2 recombinase-mediated excision of SCCmec IV (n = 5 strains) and SCCmec II (n = 2). In SCCmec IV- but not SCCmec II-containing strains, spontaneous excision of the cassette was observed. Introduction of ccrA/B type 2 recombinase genes under control of an S. aureus bacterial phage promoter in the different strains yielded excision of SCCmec II and multiple excision variants of SCCmec IV. Sequencing of the alternatively excised products in SCCmec IV strains identified a 100-bp shortened SCCmec' variant and a 5,877-bp, conserved SCC-like element that lacks mecA and ccrA/B recombinases. Excision of the SCC-like element in wild-type S. aureus was dependent on the presence of SCCmec. The element could be excised separately or as part of a novel composite cassette together with SCCmec. The relative abundance of and variety in SCCmec IV excisions may contribute to the frequency of horizontal transfer and genetic plasticity in SCCmec IV MRSA strains.     

Genotypic diversity of methicillin-resistant Staphylococcus aureus isolates in Korean hospitals

Ninety-six methicillin-resistant Staphylococcus aureus (MRSA) isolates from eight Korean hospitals were analyzed by multilocus sequence typing, SCCmec typing, and spa typing. The predominant genotype was ST5-MRSA-II of clonal complex 5, which was found in 36 isolates from six hospitals, but ST239-MRSA-III was also common. Overall, results showed a notable genotypic diversity of MRSA strains circulating in Korean hospitals.     

耐甲氧西林金黄色葡萄球菌耐药基因及致病毒素基因的研究进展

金葡菌是临床最常见的病原菌之一,在临床分离菌中分离率位居前列,其中以MRSA临床意义尤为重要。由于其多重耐药性和易造成医院感染的暴发流行,已成为临床抗感染治疗的一大难题。金葡菌可引起一系列的化脓性感染、食物中毒及中毒性休克综合征等,其化脓性感染从小的皮肤感染病变如疖、痈到严重的感染如组织坏死、坏死性肺炎、骨髓炎和心内膜炎等。     

高水平莫匹罗星耐药MRSA体外生物膜形成能力及相关基因检测

目的 了解高水平莫匹罗星耐药甲氧西林耐药金葡菌(MuH MRSA)体外生物膜形成能力及介导生物膜形成相关基因的分布.方法 对分离自上海和浙江省温州地区5所教学医院的803 株临床分离MRSA进行莫匹罗星纸片扩散法检测最低抑菌浓度(MIC),mupA基因PCR扩增筛选MuH MRSA,分光光度计检测MuH MRSA菌株体外生物膜的形成能力,PCR扩增生物膜形成相关基因(icaA、icaD、agr、sarA、sasG、bap和ccpA).结果 共筛选出53株MuH MRSA,其中仅5株(9.4%,5/53)具有体外形成生物膜的能力;基因检测显示,icaD和agr基因存在于全部MuH MRSA菌株中,而icaA、sarA、sasG和ccpA基因则分别存在于83.0%、86.8%、84.9%和92.5%的菌株中,仅有1株细菌携带bap基因.结论 大部分生物膜形成相关基因广泛分布于MuH MRSA菌株中,但仅agr基因可能是该类菌株体外生物膜形成能力的主要影响因素.     

Widespread quinolone resistance among methicillin-resistant Staphylococcus aureus isolates in a general hospital.

Ofloxacin and ciprofloxacin resistance (MIC, greater than 4 micrograms/ml) was encountered in 45 of 50 clinical isolates of methicillin-resistant Staphylococcus aureus. None of 20 methicillin-susceptible strains was resistant to the quinolones (P less than 10(-6). Quinolone-susceptible and -resistant isolates did not differ with respect to culture source or bacteriophage type. The future usefulness of quinolones for S. aureus infection may be limited.