A novel methicillin-resistance cassette in community-acquired methicillin-resistant Staphylococcus aureus isolates of diverse genetic backgrounds

Until recently, it has been unclear whether community-acquired (CA) methicillin-resistant Staphylococcus aureus (MRSA) isolates represent the spread of hospital MRSA isolates into the community. In 2 CA-MRSA isolates, a novel genetic element, designated staphylococcal cassette chromosome mec (SCCmec) type IV, was found; it differs from SCCmec types I-III in its small size and absence of non-beta-lactam genetic-resistance determinants. To study the prevalence of type IV SCCmec, polymerase chain reaction characterization of SCCmec was performed on DNA from 12 CA-MRSA isolates. The 12 CA-MRSA isolates were from diverse genetic backgrounds, as evidenced by their stratification into 5 pulsed-field gel electrophoresis types, 4 coagulase types, and 2 ribotypes. Eleven of the 12 isolates contained the novel SCCmec type IV element. Ten were resistant only to beta-lactam antibiotics. SCCmec type IV is present on the genome of CA-MRSA isolates. Its relatively small size and presence in isolates of diverse genetic backgrounds suggest that it may spread among S. aureus isolates.     

猪源耐甲氧西林金黄色葡萄球菌的耐药表型及其SCCmec基因分型研究

目的 了解上海猪场及屠宰场耐甲氧西林金黄色葡萄球菌(MRSA)的流行状况、耐药谱特征及其SCCmec基因分型特点。方法 我们于2011年8月—2012年5月分别在上海市5个规模化猪场和1个屠宰场,采集猪鼻腔拭子样品共计232份。通过7.5%氯化钠肉汤预增菌,显色培养基显色培养分离金黄色葡萄球菌(SA),采用双重PCR方法扩增其中是否含有nuc基因和mecA基因进行MRSA鉴定;以肉汤稀释法进行药物敏感性试验;应用多重PCR方法进行SCCmec基因分型;同时检测杀白细胞素(PVL)基因。结果 共计分离得到139株SA,其中70株MRSA,MRSA的检出率为30.2%(70/232)。基因分型显示均为SCCmecⅣb型,未检测到PVL基因,药敏结果显示MRSA除对利奈唑胺,万古霉素,阿米卡星全部敏感外,对头孢噻呋,庆大霉素,诺氟沙星耐药率分别为74.3%,62.9%和42.9%,对阿奇霉素,红霉素,氟苯尼考,氯霉素,苯唑西林的耐药率均为100%,值得注意的,本研究中分离的全部MRSA都对截短侧耳类药物泰妙菌素、沃尼妙林以及人医新药瑞他帕林表现高水平耐药。结论 结果显示了上海地区猪源MRSA主要流行SCCmecⅣb型,并且具有多重耐药的特点,尤其对截断侧耳类人医新药全部耐药,这也提示我们要防控动物源耐药菌或耐药基因通过食物链或者环境向人类的传播的潜在风险。     

甲氧西林耐药的金黄色葡萄球菌感染一例并文献复习

目的 通过对1例金黄色葡萄球菌染色体基因盒(SCCmec)Ⅴ型的甲氧西林耐药的金黄色葡萄球菌(MRSA)感染病例的分析,增强对MRSA社区或医院获得性感染的认识.方法 对2008年6月19日北京医院皮肤科收治、呼吸科会诊的1例SCCmec Ⅴ型的MRSA感染病例分离自血及痰标本的3株MRSA菌株进行培养及体外药物敏感试验.应用PCR方法对分离菌株进行甲氧西林耐药性决定因子A(mec A)基因鉴定和杀白细胞素(PVL)基因检测,应用多重PCR方法对其进行SCCmec分型.结果 患者男,73岁,因剥脱性皮炎入院,病程中出现MRSA败血症,继之出现双侧肺炎,最终因感染性休克死亡.药物敏感试验结果显示,该MRSA菌株除对β-内酰胺类抗生素耐药外,对其他抗生素如克林霉素敏感,对莫西沙星、庆大霉素为中介性耐药.分离的3株MRSA均属于SCCmec β型.结论 该患者为医院获得性MRSA感染,但其菌株具有社区获得性MRSA的特点,临床医师应注意鉴别.     

Preliminary report of SCCmec-types and antimicrobial susceptibilities of methicillin-resistant Staphylococcus aureus isolates from a university hospital in Thailand

Methicillin-resistant Staphylococcus aureus (MRSA) has spread worldwide. It is a major cause of hospital-acquired infections in most hospitals for nearly half century. The present study was conducted to examine the antimicrobial susceptibilities and staphylococcal cassette chromosome mec (SCCmec)-type for MRSA isolates from 237 patients treated at Srinagarind Hospital between September 2002 and August 2003. Antimicrobial susceptibility testing for all isolates was performed using an agar dilution method and SCCmec-types of 81 representatives from 237 isolates were determined using multiplex PCR. The minimum inhibitory concentration (MIC) ranges for the MRSA isolates were as follows: cefazolin 8 to > or =64; erythromycin < or = 0.5 to > or =64; gentamicin < or = 0.5 to > or =64; imipenem < or = 0.5 to >16; ofloxacin < or = 0.5 to > or =64; oxacillin 16 to > or =64; tetracycline 2 to > or =64 and vancomycin < or = 0.5 to 2 microg/ml. All MRSA isolates were susceptible to vancomycin, but only 0.4% to 8.9% was susceptible to the remaining antimicrobial agents. Of the 81 isolates tested, 2 types of SCCmec were found (76 with type III and 2 with type II) and no mecA gene was detected in 3 isolates. Sixty-seven of the 78 isolates carried the mercury-resistant operon. The multilocus sequence type in isolates with type III SCCmec was ST239 and in isolates with type II SCCmec was ST5.     

Community-onset methicillin-resistant Staphylococcus aureus in an urban HIV clinic

OBJECTIVES: To determine the proportion of skin/soft tissue infections (SSTIs) and to determine risks for MRSA infection caused by methicillin-resistant Staphylococcus aureus (MRSA) in HIV-infected out-patients. METHODS: We conducted a prospective study of SSTIs in HIV-infected out-patients. A questionnaire was used to record MRSA risk factors and treatment. In vitro testing for antibiotic susceptibility, inducible clindamycin resistance, panton-valentine leucocidin (PVL) toxin, and the staphylococcal chromosomal cassette mec (SCCmec) type was performed using standardized methods. Treatment outcomes included resolution of primary site of infection, nonresolution of infection and reinfection and were confirmed at clinic visit and/or telephone follow-up. RESULTS: Forty-one of 44 patients had an SSTI caused by MRSA. African-Americans comprised 21 of 41 MRSA patients. The median CD4 count of MRSA patients was 411 cells/microL. Four patients required hospitalization and three patients had secondary bacteraemia. Twenty-one of 41 MRSA patients had healthcare-associated (HCA) MRSA risk factors including a history of prior MRSA infection (n=9) and hospitalization within 6 months (n=11). Other prevalent MRSA risk factors included receipt of systemic antibiotics within 6 months (n=21) and previous incarceration (n=19). Twenty-two patients had a significant non-HIV-related comorbid illness. The majority of isolates were susceptible to trimethoprim-sulfamethoxazole, tetracycline, and clindamycin. Inducible clindamycin resistance was detected in 0 of 16 erythromycin-resistant, clindamycin-susceptible MRSA isolates. Twenty-one of 24 isolates tested positive for SCCmec type IV. Twenty-four of 24 isolates tested positive for the PVL gene. Antibiotic treatment was discordant (bacteria nonsusceptible to antibiotic used) in eight MRSA patients. The primary SSTI resolved in 37 of 40 MRSA patients. Recurrence of infection at a site other than the primary site was relatively common (11 patients). CONCLUSIONS: We found a high rate of MRSA causing SSTI in community-dwelling patients. The majority of isolates were positive for PVL and SCCmec IV, which is typical of community-associated MRSA isolates causing SSTIs in the general population. Inducible clindamycin resistance was not detected. Most patients had MRSA risk factors. The initial site of infection resolved in most cases but subsequent MRSA infection was relatively common.     

Usefulness of the restriction-modification test plus staphylococcal cassette chromosome mec types and Panton-Valentine leukocidin encoding phages to identify Staphylococcus aureus methicillin-resistant clones

We studied the usefulness of the restriction-modification (RM) test, staphylococcal cassette chromosome (SCC) mec types, and Panton-Valentine leukocidin (PVL)-encoding phages to identify Staphylococcus aureus methicillin-resistant lineages and to differentiate clones that belong to the same lineage. A total of 108 methicillin-resistant S. aureus (MRSA) strains were characterized by pulsed-field gel electrophoresis (PFGE)--multi-locus sequence typing (MLST)--spa-typing. The RM correctly identified the lineages CC5, CC8, CC30, and CC398, but not CC25 and CC72. The SCCmec and RM combined analysis allowed differentiation between MLST types within the same lineage. Only 5 MRSA strains were PVL-positive. Four PVL-positive USA300 isolates carried elongated-head type PVL-encoding phages, while the sequence type (ST)-30 strain carried an icosahedral-head phage. The combination of the RM test method, SCCmec types, and PVL phage identification could be useful for MRSA typing purposes.     

Clonal types and antimicrobial resistance profiles of methicillin-resistant Staphylococcus aureus isolates from hospitals in south Brazil

In the present study were evaluated the DNA macrorestriction profile and SCCmec types for nine multi-resistant MRSA selected. Also antimicrobial susceptibility testing by disk diffusion method was evaluated for 68 MRSA isolates against 12 antimicrobial agents. The isolates were recovered from blood culture collected from hospitalized patients in three hospitals of Porto Alegre, Brazil. PFGE and PCR for mecA and SCCmec I, II, III, IV types genes were done on selected nine isolates with susceptibility only to vancomycin, teicoplanin and linezolid. Two clone profiles, with five subtypes, were demonstrated among multi-resistant MRSA analyzed. Eight isolates showed harbor SCCmec type III and one isolate was not typeable. The knowledge of SCCmec type, clone and antimicrobial profiles among S. aureus is essential mainly to prevention and control of dissemination of the antimicrobial resistance.     

引起皮肤软组织感染的杀白细胞素阳性社区获得性耐甲氧西林金黄色葡萄球菌分子特征研究

目的 了解分离自临床皮肤和软组织感染(SSTIs)患者携带杀白细胞素基因(pvl)社区获得性耐甲氧西林金黄色葡萄球菌(pvl⁺-CA-MRSA)的分子特征。方法 从SSTIs患者中分离出92株CA-MRSA。采用聚合酶链反应(PCR)和测序检测pvl基因及其突变。pvl⁺-CA-MRSA菌株进行序列类型(STs)与克隆复合物(CCs)、葡萄球菌盒式染色体mec(SCCmec)、葡萄球菌蛋白基因(spa)多态性、辅助基因调控子(agr)位点、脉冲场凝胶电泳(PFGE)分型和多位点序列分型(MLST)。采用VITEK-2 Compact全自动微生物鉴定系统进行CA-MRSA药物敏感试验。结果 92株CA-MRSA中,24株(26.1%)为pvl⁺-CA-MRSA,其中91.7%(22/24)为pvl的H亚型,68株(73.9%)为未携带pvl基因CA-MRSA(pvl^--CA-MRSA)。24株pvl⁺-CA-MRSA中,共有8种STs和7种CCs,其中以ST59(62.5%,15...     

Community‐acquired,methicillin‐resistant Staphylococcus aureus isolated from children with community‐onset pneumonia in China

Community‐acquired, methicillin‐resistant Staphylococcus aureus (CA‐MRSA) has been associated with morbidity and mortality in various countries. In this study, we characterized the molecular and clinical features of pediatric CA‐MRSA pneumonia in China. Between June 2006 and February 2008, 55 previously healthy children confined in eight hospitals countrywide were found to be afflicted with CA‐MRSA pneumonia. A total of 55 strains collected from these children were analyzed by multilocus sequence typing (MLST), Staphylococcus cassette chromosome mec (SCCmec) typing, and spa typing. The Panton–Valentine leukocidin (PVL) gene was also detected. Overall, nine STs were obtained, with ST59 (40.4%) established to be the most prevalent type. We first registered the new ST1409 from a child with necrotizing pneumonia. SCCmecIVa was the most predominant type, followed by SCCmec type V. Twelve spa types were identified, of which one new spa type, t5348, was first detected and registered. One typical livestock‐associated spa type, t034, was found in a 4‐month‐old girl living in the countryside. We also found that 40% of those isolates were PVL‐positive. In addition, the median age of the children in this study was 10 months. A total of 69% (38/55) of the children with community‐acquired pneumonia (CAP) had preceding influenza or influenza‐like illness, and three ST910‐MRSA‐IV strains (PVL gene‐positive) were associated with severe necrosis. The results indicated that the recent CA‐MRSA found in Chinese children with CAP was largely associated with the spread of the ST59‐MRSA‐IV clone, and most of the PVL‐positive strains in this study did not cause necrotic cases. Pediatr Pulmonol. 2010; 45:387–394. © 2010 Wiley‐Liss, Inc.     

呼吸重症监护室耐甲氧西林金黄色葡萄球菌分子流行病学调查

目的 调查呼吸重症监护室(RICU)病房耐甲氧西林金黄色葡萄球菌(MRSA)来源、分子分型及药敏,并提供治疗建议.方法 选取成都医学院第一附属医院RICU病房2017年1月至2020年12月从43例病人痰标本、肺泡灌洗液、血液、尿液标本等分离出的52株MRSA,统计标本来源.采用琼脂稀释法进行药敏试验;采用多位点序列分...     

Potential associations between hematogenous complications and bacterial genotype in Staphylococcus aureus infection

BACKGROUND: The impact of bacterial clonality on infections caused by Staphylococcus aureus is unclear. METHODS: Three hundred seventy-nine S. aureus isolates (125 methicillin-resistant S. aureus [MRSA] and 254 methicillin-susceptible S. aureus [MSSA]) were genotyped by spa typing and multilocus sequence typing. For MRSA isolates, the staphylococcal chromosomal cassette mec (SCCmec) element was also typed. Three clinical categories were identified: nasal carriage only (n=118), uncomplicated infection (n=104), and bacteremia with hematogenous complications (n=157). RESULTS: By use of eBURST, 18 clonal complexes (CCs) were found in 371 isolates. Eight CCs accounted for 89% of isolates and occurred in all clinical categories. CC5 (P=.0025) and CC30 (P=.0308) exhibited a significant trend toward more frequent hematogenous complications. Isolates within spa types 2 and 16 showed the same significant trend and grouped within CC5 and CC30, respectively. SCCmec II isolates also showed the same significant trend compared with SCCmec IV; 96% were CC5 or CC30. CONCLUSIONS: Although most S. aureus genotypes exhibited the capacity to cause invasive disease, strains within CC5 and CC30 exhibited a significant trend toward increasing levels of hematogenous complications. Isolates within these CCs were also implicated by use of spa and SCCmec typing. The genetic determinants underlying these findings remain to be demonstrated.     

Environmental methicillin-resistant Staphylococcus aureus in a veterinary teaching hospital during a nonoutbreak period

Concurrent to reports of zoonotic and nosocomial transmission of methicillin-resistant Staphylococcus aureus (MRSA) in veterinary settings, recent evidence indicates that the environment in veterinary hospitals may be a potential source of MRSA. The present report is a cross-sectional study to determine the prevalence of MRSA on specific human and animal contact surfaces at a large veterinary hospital during a nonoutbreak period. A total of 156 samples were collected using Swiffers(?) or premoistened swabs from the small animal, equine, and food animal sections. MRSA was isolated and identified by pre-enrichment culture and standard microbiology procedures, including growth on Mueller-Hinton agar supplemented with NaCl and oxacillin, and by detection of the mecA gene. Staphylococcal chromosome cassette mec (SCCmec) typing and pulsed-field gel electrophoresis profile were also determined. MRSA was detected in 12% (19/157) of the hospital environments sampled. The prevalence of MRSA in the small animal, equine, and food animal areas were 16%, 4%, and 0%, respectively. Sixteen of the MRSA isolates from the small animal section were classified as USA100, SCCmec type II, two of which had pulsed-field gel electrophoresis pattern that does not conform to any known type. The one isolate obtained from the equine section was classified as USA500, SCCmec type IV. The molecular epidemiological analysis revealed a very diverse population of MRSA isolates circulating in the hospital; however, in some instances, multiple locations/surfaces, not directly associated, had the same MRSA clone. No significant difference was observed between animal and human contact surfaces in regard to prevalence and type of isolates. Surfaces touched by multiple people (doors) and patients (carts) were frequently contaminated with MRSA. The results from this study indicate that MRSA is present in the environment even during nonoutbreak periods. This study also identified specific surfaces in a veterinary environment that need to be targeted when designing and executing infection control programs.     

Complex molecular epidemiology of methicillin-resistant staphylococcus aureus isolates from children with cystic fibrosis in the era of epidemic community-associated methicillin-resistant S aureus

BACKGROUND: Limited data exist about the molecular types of methicillin-resistant Staphylococcus aureus (MRSA) strains found in children with cystic fibrosis (CF). We sought to characterize MRSA strains from these patients and compare them with MRSA strains from non-CF pediatric patients. METHODS: All MRSA isolates were collected prospectively at Children's Medical Center in Dallas, TX, and the University of Chicago Comer Children's Hospital in 2004 to 2005. All CF MRSA isolates underwent susceptibility testing, multilocus sequence typing, Panton-Valentine leukocidin gene detection (pvl+), and staphylococcal chromosome cassette mec (SCCmec) typing. RESULTS: A total of 22 of 34 MRSA isolates (64.7%) from patients with CF belonged to clonal complex (CC) 5 and contained SCCmec II, so-called health-care associated MRSA (HA-MRSA) strains. Nine of 34 MRSA strains (26.5%) were CC 8, and contained SCCmec IV, so-called community-associated MRSA (CA-MRSA) strains. The CA-MRSA strains tended to be isolated from newly colonized CF patients. In contrast, CC8 isolates predominated among the non-CF patients (294 of 331 patients; 88.8%). MRSA isolates from children with CF were more likely to be resistant to clindamycin (65% vs 19%, respectively) and ciprofloxacin (62% vs 17%, respectively) compared with strains from non-CF patients (p < 0.001). There was no difference in the rate of pvl+ isolate recovery from children with CF undergoing a surveillance culture (7 of 23 children) compared with those with pulmonary exacerbation (3 of 11 children; p = 1.0). CONCLUSIONS: Both CA-MRSA (CC8) isolates and HA-MRSA (CC5) isolates populate the respiratory tracts of children with CF. HA-MRSA isolates predominated, but CA-MRSA strains predominated among CF patients with newly acquired MRSA strains and among the non-CF patients. The presence of CA-MRSA strains in children with CF was not associated with exacerbation or necrotizing pneumonia.     

What is community-associated methicillin-resistant Staphylococcus aureus?

BACKGROUND: A community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infection has been defined as an MRSA infection in a patient who lacks specific risk factors for healthcare exposure. We sought to determine whether the absence or presence of these risk factors still predicts the phenotypic or genotypic characteristics of MRSA strains. METHODS: All clinical MRSA isolates were prospectively collected at the University of Chicago Hospitals from July 2004 through June 2005. Patients were interviewed and/or their medical records were reviewed. Isolates underwent genotyping and susceptibility testing. Data on patients and isolates were stratified in accordance with 8 frequently cited criteria for the identification of CA-MRSA and compared for concordance. RESULTS: Among 616 unique patients from whom MRSA isolates were recovered, 404 (65.6%) had risk factors for healthcare exposure. Of the 404 isolates recovered from these patients, 166 (41.1%) were clindamycin susceptible, 190 (47.0%) carried staphylococcal cassette chromosome mec (SCCmec) type IV, 145 (35.9%) carried the Panton-Valentine leukocidin genes (PVL+), and 162 (40.1%) were identified as sequence type (ST) 8 by multilocus sequence typing (MLST), all of which are characteristics commonly attributed to CA-MRSA strains. CONCLUSIONS: Association with the healthcare environment now has little predictive value for distinguishing patients with infection due to multidrug resistant MRSA isolates from those infected by CA-MRSA isolates, that is, isolates that are clindamycin-susceptible, PVL+, ST8, and/or contain SCCmec type IV. Defining CA-MRSA by the absence of risk factors for healthcare exposure greatly underestimates the burden of epidemic CA-MRSA disease.     

Roles of 34 virulence genes in the evolution of hospital- and community-associated strains of methicillin-resistant Staphylococcus aureus

BACKGROUND: The extent to which the horizontal transfer of virulence genes has contributed to the emergence of contemporary virulent strains of methicillin-resistant Staphylococcus aureus (MRSA) in hospital and community settings is poorly understood. METHODS: Epidemiologically well-characterized MRSA isolates collected over 8.5 years were genotyped and tested for the presence of 34 virulence genes. RESULTS: Six strain types accounted for 88.2% of all MRSA infections. The evolution of contemporary hospital and community phenotypes within the CC8 and CC30 lineages--2 background genomes that produced historical pandemic MRSA clones--were associated with multiple horizontal acquisitions of virulence genes. The epidemic community phenotype of a CC8 strain, designated ST8:USA300, was linked to the acquisition of staphylococcal cassette chromosome (SCC)mec type IV, the genes for Panton-Valentine leukocidin (PVL), and the enterotoxin Q and K genes. Similarly, the epidemic community phenotype of a CC30 strain, ST30:USA1100, was linked to the acquisition of SCCmec type IV and the pvl genes. In contrast, the epidemic hospital phenotype of another CC30 strain, ST36:USA200, was associated with the acquisition of SCCmec type II, the enterotoxin A gene, and the toxic shock syndrome toxin 1 gene. The pvl genes appear not to be essential for the evolution OF other community-associated strains of mrsa, including ST8:USA500 and ST59:USA1000. CONCLUSIONS: The horizontal transfer of virulence genes, although infrequent, is epidemiologically associated with the emergence of new virulent strains of MRSA.     

耐甲氧西林金黄色葡萄球菌SCCmec分型研究

摘要： 目的 分析本地区分离的耐甲氧西林金黄色葡萄球菌（MRSA）葡萄球菌盒染色体mec（SCCmec）类型。 方法 利用3套多重PCR体系扩增耐甲氧西林金黄色葡萄球菌SCCmec型特异性位点、共同位点、鉴别位点、内参照位点以及mec基因复合物和ccr基因复合物进行SCCmec分型。 结果 分离的156株MRSA中,6株MRSA不能分型,可分型率为96.2%。其中,Ⅲ型SCCmec 125株,占83.3%,Ⅱ型SCCmec 11株,占7.3%,Ⅳ、Ⅴ型SCCmec 各7株,占4.7%。 结论 本地区分离的耐甲氧西林金黄色葡萄球菌流行携带最多耐药基因的Ⅲ型SCCmec。     

Prevalence of Staphylococcus aureus nasal colonization in the United States, 2001-2002

BACKGROUND: Staphylococcus aureus is a common cause of disease, particularly in colonized persons. Although methicillin-resistant S. aureus (MRSA) infection has become increasingly reported, population-based S. aureus and MRSA colonization estimates are lacking. METHODS: Nasal samples for S. aureus culture and sociodemographic data were obtained from 9622 persons > or = 1 year old as part of the National Health and Nutrition Examination Survey, 2001-2002. After screening for oxacillin susceptibility, MRSA and selected methicillin-susceptible S. aureus isolates were tested for antimicrobial susceptibility, pulsed-field gel electrophoresis clonal type, toxin genes (e.g., for Panton-Valentine leukocidin [PVL]), and staphylococcal cassette chromosome mec (SCCmec) type I-IV genes. RESULTS: For 2001-2002, national S. aureus and MRSA colonization prevalence estimates were 32.4% (95% confidence interval [CI], 30.7%-34.1%) and 0.8% (95% CI, 0.4%-1.4%), respectively, and population estimates were 89.4 million persons (95% CI, 84.8-94.1 million persons) and 2.3 million persons (95% CI, 1.2-3.8 million persons), respectively. S. aureus colonization prevalence was highest in participants 6-11 years old. MRSA colonization was associated with age > or = 60 years and being female but not with recent health-care exposure. In unweighted analyses, the SCCmec type IV gene was more frequent in isolates from participants of younger age and of non-Hispanic black race/ethnicity; the PVL gene was present in 9 (2.4%) of 372 of isolates tested. CONCLUSIONS: Many persons in the United States are colonized with S. aureus; prevalence rates differ demographically. MRSA colonization prevalence, although low nationally in 2001-2002, may vary with demographic and organism characteristics.     

Epidemiological and microbiological analysis of community-associated methicillin-resistant Staphylococcus aureus strains isolated from a Japanese hospital

Reports of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections have recently increased in Japan; however, these studies contain limited information on their epidemiology. We performed a single-center study in the Tokyo Medical University Hospital located in Shinjuku, a central area of Tokyo, Japan. From 2,099 MRSA isolates obtained during July 2007 to March 2009, we selected 44 MRSA isolates with a MIC of <2 μg/mL for imipenem. Among 44 isolates, 28 strains had type IV or type V SCCmec, and we classified them as CA-MRSA. We identified only 1 Panton-Valentine leukocidin (PVL)-positive MRSA strain, which belonged to SCCmec type V. The PVL-positive CA-MRSA strain was isolated from a patient with multiple subcutaneous abscesses. The patient had returned to Japan from India; thus, the strain may have been contracted from outside of Japan. Thirteen (46.4%) and 15 strains (53.6%) were isolated from outpatients and inpatients, respectively. The major sites of infection included the respiratory tract (8 strains, 28.6%), skin/soft tissue (4 strains, 14.3%), and nasal cavity (4 strains, 14.3%). It is important to note that the most common site of CA-MRSA infection in inpatients was the respiratory tract; respiratory infections with CA-MRSA frequently cause severe infectious diseases.     

烧伤患者创面感染金黄色葡萄球菌分离株耐药性及流行病学分析

目的对河北地区烧伤患者创面分离的120株金黄色葡萄球菌进行mecA和SCCmec检测分析MRSA耐药机制,为临床合理用药提供依据。方法在2009~2013年收治的烧伤患者创面中分离的120株金黄色葡萄球菌,采用头孢西丁纸片法进行MRSA筛选,对mecA基因,SCCmec和spa基因进行PCR扩增以及分型。结果 120株金黄色葡萄球菌中有74株为MRSA,占61.7%。药敏试验显示,MRSA对16种临床常见抗生素耐药率,超过85%的有7种,依次为苯唑西林（98.6%）,青霉素（96.0%）,环丙沙星（94.6%）,阿莫西林和头孢唑林（89.2%）,亚胺培南（87.8%）,庆大霉素（85.1%）,另有1株对万古霉素耐药。结论本组金黄色葡萄球菌MRSA检出率较高,并表现出较高的耐药性。MRSA具有的多重耐药性mecA基因密切关系。     

The arginine catabolic mobile element and staphylococcal chromosomal cassette mec linkage: convergence of virulence and resistance in the USA300 clone of methicillin-resistant Staphylococcus aureus

The epidemic character of community-associated methicillin-resistant Staphylococcus aureus, especially the geographically widespread clone USA300, is poorly understood. USA300 isolates carry a type IV staphylococcal chromosomal cassette mec (SCCmec) element conferring beta-lactam antibiotic class resistance and a putative pathogenicity island, arginine catabolic mobile element (ACME). Physical linkage between SCCmec and ACME suggests that selection for antibiotic resistance and for pathogenicity may be interconnected. We constructed isogenic mutants containing deletions of SCCmec and ACME in a USA300 clinical isolate to determine the role played by these elements in a rabbit model of bacteremia. We found that deletion of type IV SCCmec did not affect competitive fitness, whereas deletion of ACME significantly attenuated the pathogenicity or fitness of USA300. These data are consistent with a model in which ACME enhances growth and survival of USA300, allowing for genetic "hitchhiking" of SCCmec. SCCmec in turn protects against exposure to beta-lactams.