Phenotypic characterization and prevalence of enterotoxin genes in Staphylococcus aureus isolates from outbreaks of illness in Chengdu City

Staphylococcus aureus produces a spectrum of enterotoxin that is recognized as the main reason for causing staphylococcal food poisoning. The aim of the current study was to investigate the phenotypic characteristics and enterotoxin genotypes of S. aureus isolated from food poisoning sufferers. On the basis of the amplification of 16S rRNA and nuc gene specific to S. aureus assay and the phenotype (hemolytic activity, thermal stable nuclease [Tnase] test, and biofilm formation), all isolates were identified as S. aureus. To genotypically characterize S. aureus isolates, genes encoding staphylococcal enterotoxin (sea, seb, sec, sed, see, seg, seh, sei, sej, sek, sem, sen, ser, and seu) were investigated by using polymerase chain reaction technique. The results showed that the eight isolates of S. aureus had different enterotoxin genotypic characteristics, which was the main cause of food poisoning. One isolate contained 10 enterotoxin genes, and the other 7 isolates carried 3 or more enterotoxin genes. The frequency of the newly identified enterotoxin genes (seg-seu) was higher than classical genes (sea-see). Overall, multi-gene detection rates were 75% (for sek, ser, and seu); 50% (for sea and sem); 37.5% (for sen, seg, and sei); and 12.5% (for seb, sec, sed, and sej), respectively. The see and seh gene were not detected in any isolates. The current study provided the exact distribution of enterotoxin genes in eight S. aureus strains from food poisoning sufferers, which indicated that the pathogenicity of the newly identified enterotoxin should be highlighted. The need for prevention of food poisoning occurrences caused by enterotoxin of S. aureus should be reinforced.     

Characterization of toxin genes and antimicrobial susceptibility of Staphylococcus aureus isolates from Louisiana retail meats

Staphylococcus aureus is a leading cause of food poisoning worldwide due to the production of heat-stable enterotoxins. Recently, the isolation of methicillin-resistant S. aureus (MRSA) from food animals and retail meats raised additional food safety concerns. In this study, we characterized 152 S. aureus isolates, including 22 MRSA recovered from Louisiana retail pork and beef meats, for the prevalence of nine enterotoxin and four other exotoxin genes by polymerase chain reaction and antimicrobial susceptibility testing by broth microdilution. Overall, 85% of S. aureus isolates were positive for at least one of six enterotoxin genes identified and 66% harbored two to four enterotoxin genes. The two most predominant ones were seg and sei (66% each), followed by seh (20%), sed (15%), sej (13%), and sea (1%). No isolates harbored enterotoxin genes seb, sec, or see, the toxic shock syndrome toxin 1 gene tst, or the exfoliative toxin genes eta or etb. Three MRSA isolates were the only ones harboring Panton-Valentine leucocidin. Resistances were common to penicillin (71%), ampicillin (68%), and tetracycline (67%), followed by erythromycin (30%), clindamycin (18%), oxacillin with 2% NaCl (14%), ciprofloxacin (13%), levofloxacin (13%), gentamicin (3%), quinupristin/dapfopristin (3%), chloramphenicol (2%), and moxifloxacin (1%). Multidrug resistance was commonly observed among MRSA isolates and S. aureus isolates from pork. This study demonstrated that S. aureus isolates found in Louisiana retail pork and beef meats possessed various enterotoxin genes and antimicrobial resistance profiles. Therefore, vigilant food safety practice needs to be implemented for people who handle raw meat products to prevent foodborne infections and intoxications due to S. aureus contamination.     

2013-2017年西安市食物中毒中金黄色葡萄球菌分型分析

  目的  了解2013-2017年西安市食物中毒中分离的金黄色葡萄球菌（staphylococcus aureus,S.aureus）分子流行特点。  方法  通过脉冲场凝胶电泳（pulsed field gel electrophoresis,PFGE）、多位点序列分型（multilocus sequence typing,MLST）和spa分型方法对八起食物中毒标本的26株金黄色葡萄球菌进行分子分型,运用聚合酶链式反应（polymerase chain reaction,PCR）检测相关肠毒素基因。  结果  26株S.aureus PFGE可分为7种型别（A-G）;MLST可分为3种序列型（ST6,ST5和ST59）。其中,ST6占65.38%,为主要型别;spa可分为4种型别（t437,t701,t11363和t5923）,优势型别为t701,占65.38%。肠毒素基因检测中,sea基因占76.92%（20/26）;sed-seg基因占23.08%（6/26）;其它肠毒素基因未检出。  结论  2013-2017年西安市食物中毒标本中分离培养的S.aureus的主要流行型别为ST6-t701-sea,并首次检出含有seg新型肠毒素基因。PFGE、MLST和spa分型三种方法相结合全面的了解菌株的分子流行特点。     

一起食物中毒事件的金黄色葡萄球菌分子分型研究

目的 运用分子分型方法分析一起在广州发生的由金黄色葡萄球菌所致的重大食物中毒事件,并进行溯源.方法 在常规分离的基础上,采用荧光定量PCR检测所获得的金黄色葡萄球菌特异耐热核酸酶基因(nuc)、耐甲氧西林决定基因(mecA)和其他5种肠毒素基因(sea,seb,sec,sed,see),并对16 S rRNA核苷酸进行序列扩增和使用DNAStar MegAlign 5.0软件分析,同时应用脉冲场凝胶电泳(PFGE)和BioNumerics Version 4.0软件进行聚类分析.结果 10株金黄色葡萄球菌特异性nuc基因均为阳性,其中7株分离菌的肠毒素sea,seb基因为阳性,分离菌可以分为4个16 SrRNA型别和5个PFGE型别.结论 本次食物中毒事件至少由3株以上亲缘关系相近的产毒金黄色葡萄球菌污染食物所致,分子分型方法可以为疫情溯源提供分子流行病学证据和支持.     

金黄色葡萄球菌污染冰淇淋的调查

目的 通过冰淇淋及其各种原料和生产线样本分离、培养金黄色葡萄球菌,分析分离株的分子分型和表型特征,对金黄色葡萄球菌污染冰淇淋进行调查.方法 采集冰淇淋及其各种原料和生产线投料口、切片机出口、成品托盘等样本,用国标方法分离、培养、鉴定金黄色葡萄球菌,VITEK32生化验证,Mini-Vidas检测分离株肠毒素(多克隆肠毒素SEA-SEE),PCR检测分离株肠毒素基因(肠毒素SEA-SE:J基因),VITEK32测定分离菌株抗生素的耐药性,脉冲凝胶电泳(PFGE)分析菌株间的基因指纹图谱特征.结果 分别从冰淇淋和切片机出口分离到2株金黄色葡萄球菌.它们都含有肠毒素(多克隆肠毒素SEA-SEE),都有SEC、SED、SEG、SEH、SEI和SEJ肠毒素基因,耐药谱相同,脉冲凝胶电泳(PFGE)的指纹图谱相同.结论 污染冰淇淋和切片机出口的金黄色葡萄球菌是同一克隆株,切片机出口的污染导致冰淇淋污染.     

基于WGS的学生与环境MRSA菌株间毒素基因的相互关联分析

目的 探究学生鼻腔和学校环境耐甲氧西林金黄色葡萄球菌(methicillin-resistant staphylococcus aureus, MRSA)的毒素基因情况及遗传相似性。方法 利用全基因组测序技术,比较广州市8所小学学生和环境中MRSA的毒素基因情况。采用χ²检验或Fisher确切概率法分析毒素基因种类和数目的差异,构建系统进化树和聚类分析比较学生与环境的毒素基因谱。结果 检出的135株MRSA中,学生与环境均携带以溶血毒素(hlgA、hlgB、hlgC)(96.88%～100.00%)和胞外酶基因(aur)(98.06%～100.00%)为主的毒素基因。在种类上,34种毒素基因除部分肠毒素基因(sec3、seg、sei、sem、sen、seo、seu)外,其余均无统计学差异(P>0.05);在携带基因数目上,除携带12种毒素基因在二者之间有差异(χ²=12.35,P<0.001),其余均无差异(P>0.05)。此外,hlgA-hlgB-hlgC-aur-scn-sak和seg-sei-sem-sen-seo-s...     

金黄色葡萄球菌食品和病人分离株肠毒素基因和耐药性比较

目的：对金黄色葡萄球菌食品（不含生牛奶）分离株和病人分离株的肠毒素基因进行分型和耐药性检测,比较两种分离菌株的肠毒素基因分布和耐药性差异。方法：用国标方法分离鉴定金黄色葡萄球菌,VITEK32生化验证,PCR检测金黄色葡萄球菌肠毒素基因（肠毒素SEA-SEJ基因）,VITEK32测定分离菌株抗生素的耐药性。结果：从病人分离的80株金黄色葡萄球菌检测到9种基因。肠毒素基因携带率为85.0%,同时携带2种及以上毒素基因的菌株占76.3%,含传统肠毒素基因（SEA-SEE）的菌株占43.8%,有新发现肠毒素基因（SEG-SEJ）的菌株占71.3%。从食品中分离的51株金黄色葡萄球菌检测到7种肠毒素基因。肠毒素基因携带率为68.7%,同时携带2种及以上毒素基因的菌株占21.6%。有SEA基因的占27.5%,含其它传统的毒素基因类型（SEB-SEE）基因的菌株占23.5%,携带新发现的毒素基因SEG、SEH、SEI的菌株只占9.8%。金黄色葡萄球菌病人分离株与食品分离株的耐药谱和耐药率有较大差异。结论：金黄色葡萄球菌食品分离株和病人分离株的肠毒素基因分布不同,其耐药性有明显区别。     

应用实时荧光PCR技术检测金黄色葡萄球菌肠毒素基因

目的:建立一种简便、特异的荧光PCR检测方法,用于金黄色葡萄球菌肠毒素的检测。方法:按金黄色葡萄球菌SEA～SEE型肠毒素基因序列设计引物,在普通PCR检测体系中,加入SYBR Green I荧光染料,建立荧光PCR检测体系。结果:46株金黄色葡萄球菌中检出22株携带肠毒素基因,阳性率为47.83%。以SEA、SEB检出率较高,分别为31.82%和27.27%;不同来源的分离株携带肠毒素基因的比例不同,同时携带2种及以上毒素基因的菌株占27.27%。结论:荧光PCR检测金黄色葡萄球菌肠毒素的方法具有快速、敏感、特异性高的特点,适用于肠毒素基因的分型与分布的研究,适合基层疾控部门使用。     

Genotypic analysis of Staphylococcus aureus from milk of dairy cows with mastitis in Argentina

Staphylococcus aureus is the most prevalent pathogen causing mastitis of dairy ruminants. This study was developed to ascertain the genotypes and genealogical relationship among strains isolated from milk of bovines with mastitis in Argentina. Molecular epidemiological analysis of S. aureus was performed on 112 isolates from 21 districts. Clonality was assessed by SmaI pulsed-field gel electrophoresis (PFGE) typing, automated EcoRI ribotyping and restriction enzyme analysis of plasmid (REAP) DNA profiles. A total of 22 band patterns distributed in four clusters were found by SmaI PFGE analysis. The similarity of clusters 2, 3 and 4 with cluster 1 was 0.73, 0.69 and 0.33, respectively, and 101 of 112 isolates belonged in cluster 1. PFGE band patterns from 42 isolates within cluster I were indistinguishable from each other (type A). The second largest group of isolates with indistinguishable PFGE band patterns was subtype A11, which was composed of 19 isolates. Automated ribotyping assigned the 112 isolates into 13 ribotypes. Among these, the most prevalent ribotypes I and VI were composed of 49 and 35 isolates respectively. Although there was certain correspondence between PFGE genotypes and ribotypes, further discrimination was achieved by combining both methods. REAP DNA profile analysis was useful to provide even further discrimination between isolates with identical PFGE genotype and ribotype. The most prevalent S. aureus strains A/I and A11/VI were widely distributed in the country and were not restricted to individual nearby locations. Prevalence of these two strains varied consecutively within a period of 8 years. Whether the shift in type prevalence was due to selection of a phenotypic trait remains undisclosed.     

Antimicrobial susceptibility testing and genotypic characterization of Staphylococcus aureus from food and food animals

Staphylococcus aureus is commonly present in humans and animals. The aim of this study was to investigate antimicrobial resistance and genetic characteristics of S. aureus from food and food animals in Shaanxi Province in China. A total of 332 nasal swabs, breast skin swabs, raw milk, and pork samples were collected from local pig, dairy farms, or local grocery stores and screened for the presence of S. aureus. S. aureus isolates were characterized using antimicrobial susceptibility, pulsed-field gel electrophoresis (PFGE) analysis, and polymerase chain reaction for detecting pvl and mecA genes. Methicillin-resistant S. aureus (MRSA) strains were additionally tested for SCCmec type and exfoliative toxin genes. The prevalence of S. aureus was 30.6% in pig nasal swabs, 32.5% in pork, 25.7% in cow nasal swabs, 30.8% in cow breast skin swabs, and 29.3% in milk samples. Resistances were common among isolates tested against erythromycin (65.7%), tetracycline (65.7%), ciprofloxacin (52.7%), followed by gentamicin (36.7%), chloramphenicol (23.1%), cefoxitin (8.3%), and oxacillin (7.7%), but no isolate was resistant to vancomycin, amikacin, or cefoperazone. pvl gene was found in the isolates from all types of samples except from cow nasal swabs. Fourteen isolates from pig nasal swabs contained mecA gene and were considered as MRSA. PFGE analysis showed that nasal isolates differed from food isolates, but isolates from the same animal source appeared to cluster closely. The PFGE patterns of MRSA isolates were different from other S. aureus isolates from pig nasal cavity even though they were from the same source. All the MRSA isolates belonged to SCCmec type IV(b). No isolates contained exfoliative toxin genes. These findings indicated that S. aureus, including multidrug-resistant S. aureus, are widely spread in food animals and animal-derived foods in Shaanxi Province, China. MRSA isolates from pigs may pose potential health risks for workers in swine farms and the community at large.     

食源性金黄色葡萄球菌流行特征、产肠毒素特性及耐药性研究

目的：了解食源性金黄色葡萄球菌流行特点及产肠毒素特性及其耐药性，为制定HACCP以防止金黄色葡萄球菌的食源性疾病提供依据。方法：采集8类食品1243件分离金黄色葡萄球菌并进行产肠毒素A—E试验及药物敏感试验。结果：从生肉、熟食、生奶、及水产品中分别分离出40株（10．96％）、12株（3．13％）、34株（16．27％）及1株（1．12％）金黄色葡萄球菌，相应的产肠毒素率分别达到52．50％、58．33％、61．76％、0．oo％；对青霉素、四环素、凝固酶阴性苯唑西林耐药率分别高达93．10％、49．43％、37．93％；79．31％菌株对2种以上的药物多重耐药，最多耐药种类达7种，表现出30种耐药谱。结论：扬州市食品中存在着较严重的金黄色葡萄球菌潜在的危害，主要来源于生肉、生奶及熟食；食源性金黄色葡萄球菌产毒素能力较强。金黄色葡萄球菌对多种药物的耐药性提示安全应用治疗药物的重要性。     

2017年中国部分省市即食食品来源耐甲氧西林金黄色葡萄球菌耐药性、毒力基因分布及分子分型

目的了解中国部分省市即食食品来源耐甲氧西林金黄色葡萄球菌(methicillin-resistant Staphylococcus aureus,MRSA)耐药性、毒力基因分布和脉冲场凝胶电泳(pulsed-field gel electrophoresis,PFGE)分型特征。方法收集2017年中国部分省市即食食品中分离到的397株金黄色葡萄球菌,采用聚合酶链式反应方法检测其mecA基因携带情况,对鉴定为MRSA的菌株进行耐药性和毒力基因检测,并进行脉冲场凝胶电泳分型。结果从397株金黄色葡萄球菌中检出32株mecA基因阳性菌株,即为MRSA菌株。32株MRSA对青霉素、苯唑西林和头孢西丁均表现为耐药,对其他抗生素的耐药率分别为红霉素78.1%、克林霉素65.6%、四环素53.1%、氯霉素28.1%和环丙沙星12.5%,对庆大霉素和复方新诺明的耐药率均小于10%;32株MRSA表现为11种耐药谱,其中有29株(90.6%)为多重耐药,最多可同时耐受9种抗生素(2株)。共27株MRSA检出了13种毒力基因,检出前4位的依次为sel-q(56.3%)、sel-k(43.8%)、seb(28.1%)和sec(18.8%),同一菌株可同时携带2种以上毒力基因。32株MRSA共分为26种PFGE带型,优势带型不明显。结论 2017年中国即食食品来源MRSA耐药谱广,多重耐药现象严重,且携带多种毒力基因,PFGE带型呈现多样性。     

金黄色葡萄球菌超抗原在不同人群中的分子特征研究

目的了解菌血症患者血液,医护工作者、非感染性疾病入院患者以及社区健康人群前鼻腔内的金黄色葡萄球菌超抗原基因分子特征。方法用PCR和multiplex-PCR方法对277株菌的毒性休克综合征毒素-1(toxicshock syndrome toxin-1,TSST-1)和肠毒素(staphylococcal enterotoxin,SE)编码基因进行了扩增。结果 277株分离的金黄色葡萄球菌中共有142株(51%)肠毒素基因检测结果为阳性。从医院内各人群组(包括医院菌血症患者组、医护人员组和非感染性疾病入院患者组)分离菌株的阳性率在50%~59%,要比社区健康人群组阳性率(36%)高(χ2=10.86,P<0.05)。医院内各人群组分离株的SE基因主要以A型为主,而社区健康人群组的分离菌株则以D型为优势型别。另外,菌血症患者血液的金黄色葡萄球菌携带基因tsst-1的阳性率要高于其他人群组(χ2=21.91,P<0.01)。结论本研究表明不同人群分离得到的金黄色葡萄球菌超抗原分子特点具有特异性,对临床金黄色葡萄球菌的诊断治疗和流行病学研究具有一定的指导意义。     

Enterotoxin and toxic shock syndrome toxin-1 production of methicillin resistant and methicillin sensitive Staphylococcus aureus strains

In this study the production of enterotoxin A-D and toxic shock syndrome toxin-1 (TSST-1) of 181 methicillin resistant (MRSA) and 100 methicillin sensitive (MSSA) Staphylococcus aureus first isolates from different patients was investigated. All the MRSA- and MSSA isolates in the study were collected in a period between 1993 and 1995 from specimens sent from 11 different acute care hospitals in the greater Düsseldorf area. As far as possible the isolates were matched according to ward and hospital. The isolates were collected in the same time period and matched for specimen from which isolated. Furthermore, only first isolates were analysed in both groups. No significant difference in the production of toxin of any type between MRSA and MSSA could be detected (51 and 40% respectively). When the individual toxins were analysed, again no significant difference between MRSA and MSSA was demonstrable (enterotoxin production by MRSA 40% and MSSA 36%, and TSST-1 16% and 8% respectively). Despite this, a slight tendency for MRSA to produce enterotoxin A and B and for MSSA to produce enterotoxin C was observed. In addition, generation of TSST-1 by both groups was independent of enterotoxin A-D production. Interestingly, no increase in the proportion of TSST-1- or enterotoxin-producing MRSA and MSSA isolates was observed in strains isolated from blood cultures from patients with a clinical diagnosis of sepsis. Genotypical pulsed-field-gel-electrophoresis (PFGE) and phenotypical (bacteriophage typing, lysotyping) characterization of the 181 MRSA isolates resulted in 28 different PFGE patterns (of which 19 were toxin producers) and 22 lysotyping groups (18 of which produced toxin). In summary, the investigated clinical S. aureus isolates showed no difference in their ability to produce toxin and this was independent of their sensitivity to methicillin.     

贵州省即食米面制品食源性致病菌污染及病原特征分析

目的 了解贵州省即食米面制品中食源性致病菌污染状况和病原学特征,为细菌性食源性疾病的防治提供参考依据。方法 2014—2019年在贵州省的88个县（市、区）采集即食米面制品1128份,依据食品安全国家标准（GB4789）进行五种食源性致病菌的检测;采用荧光定量PCR法和ELISA法分别检测金黄色葡萄球菌肠毒素基因及蛋白,普通PCR法检测蜡样芽胞杆菌毒力基因。结果 1128份即食米面制品有130份样品检出食源性致病菌,检出率为11.52%,分别是蜡样芽胞杆菌7.71%,金黄色葡萄球菌3.10%,沙门氏菌0.27%,单核细胞增生李斯特氏菌0.44%,未检出致泻大肠埃希氏菌。分离的35株金黄色葡萄球菌有65.71%携带肠毒素基因,54.29%呈肠毒素蛋白阳性。87株蜡样芽胞杆菌都至少携带两种以上毒力基因,同时携带hblACD及nheABC的有29.88%。结论 贵州省即食米面制品存在多种食源性致病菌污染,蜡样芽胞杆菌和金黄色葡萄球菌污染率较高且携带多种毒力基因,存在较大食源性疾病风险,监管部门应加强对即食米面制品的加工制作管理。     

金黄色葡萄球菌食物中毒菌株肠毒素检测及基因分析

目的:了解一起食物中毒中分离到的金黄色葡萄球菌(Staphylococcus aureus,SA)的生物学特性及其肠毒素基因检测。方法:采用VITEK-32全自动微生物鉴定/药敏分析系统对分离到的金黄色葡萄球菌菌株进行生化鉴定和药敏试验,并采用mini-VIDAS全自动荧光酶标免疫仪对菌株进行肠毒素检测,再采用PCR技术对产肠毒素的菌株进行基因分型。结果:总共分离到的19株金黄色葡萄球菌,所有分离株均对青霉素G耐药,均分泌β-内酰胺酶,肠毒素基因分型检测均为SEA与SEE。结论:19株分离株均携带肠毒素,经鉴定均为SEA与SEE肠毒素混合型,由此对食物中毒的原因有一个较圆满的解释。     

江西省婴幼儿谷类辅食中14种元素污染状况调查

目的 了解江西省市售婴幼儿谷类辅食中14种元素的污染状况,为食品相关部门的监管提供参考。方法 主要采集本地产婴幼儿食品,采用微波消解-电感耦合等离子质谱法进行测定;按照《食品安全国家标准 婴幼儿谷类辅助食品》（GB 10769-2010）和《关于发布婴幼儿米粉食品中镉的临时限量值的公告》对检测结果进行卫生学评价。结果 共监测122份样品,铅和砷合格率为100%,镉合格率为99.2%。14种元素均有检出,其中砷、铜、硒、镍、锰和钡的检出率均为100%,锂元素的检出率最低。各元素的含量范围为0.0015～14.1mg/kg,其中锰的平均含量最高（5.85mg/kg）,其次为铝和铜,其他元素含量均较低。结论 江西省市售婴幼儿谷类辅食中元素污染总体水平较低,但目前限量指标较少,有必要进一步完善相关标准,确保婴幼儿食品安全。     

Staphylococcus aureus of phage type 187 isolated from people occurred to be a genes carrier of eneterotoxin C and toxic shock syndrome toxin-1 (TSST-1)

The aim of this study was to examine the genotype properties of Staphylococcus aureus of phage type 187 strains that constitute a separate group among the strains of S. aureus. Sixteen strains were collected from the hospital patients (n=12) and the healthy carriers (n=4) in 13 medical centres in Poland during 1991 and 2005. Biotyping, antibiotic susceptibility, phage typing, detection the genes of enterotoxins and toxic shock syndrome toxin, genotyping of chromosomal DNA by pulsed-field gel electrophoresis (PFGE), also amplification and restriction analysis of the coagulase (coa) and the protein A genes (spa) (PCR/restriction fragment length polymorphism (RFLP)) was tested. The results of this study showed that all staphylococcus of phage type 187 belonged to the human biotype (A) and appeared to be sensitive to all of the tested antibiotics, including methicillin (MSSA). Finding out the toxin genes showed that almost all of them (93.8%) had the enterotoxin C gene (sec) and TSST-1 gene (tst). The PFGE typing proved that the phage type 187 strains (except for one) constitute one PFGE type. These results and the identical restriction patterns in the PCR/RFLP method, also the same biotype, sensitivity to antibiotics and the presence genes of the same type of toxins confirmed that the phage type 187 strains constitute one clone within our country. Additionally, the fact that almost all of them have the enterotoxin genes and tst gene allows to consider them the strains of potentially high virulence.     

Irish-1 and Irish-2: UK epidemic meticillin-resistant Staphylococcus aureus strains associated with Northern Ireland

Since 1998, an increasing number of meticillin-resistant Staphylococcus aureus (MRSA) isolates with one of two characteristic phage patterns have been referred to the authors' laboratory from Northern Ireland. These strains were designated 'Irish-1' and 'Irish-2'. Analysis of 956 submitted isolates classified as Irish-1 or Irish-2 showed that 97% of the former and 95% of the latter were from Northern Ireland. Only 0.2% and 3%, respectively, were from England. Eleven Irish-2 isolates had been referred from Western Australia as representatives of an epidemic strain originally isolated there in 1994. Ninety isolates with the Irish-1 phage pattern and 91 isolates with the Irish-2 phage pattern, from numerous hospitals, were characterized by SmaI pulsed-field gel electrophoresis (PFGE), toxin gene carriage and antibiotic susceptibility. PFGE showed that, within each collection, a few isolates represented unrelated strains, but the majority were within six band differences of the most common profiles. Half of the Irish-1 isolates were homogeneous, with 22 DNA profiles among the remainder. Irish-2 isolates had two common profiles, D1 and D2, equally divided between one-third of the isolates and differing from each other by two bands; the remaining isolates shared 31 DNA profiles. Cluster analysis showed some overlap in DNA profiles between the Irish-1 and Irish-2 strains, but clear separation from other epidemic MRSA strains. There was no obvious correlation between PFGE profile and either antibiotic resistance pattern or toxin gene possession. All but three Irish-1 isolates possessed only the staphylococcal enterotoxin A (sea) gene, whereas almost all Irish-2 isolates were negative for all 12 enterotoxin genes. Sixty-nine percent of Irish-2 isolates were resistant to ciprofloxacin, erythromycin, kanamycin, neomycin and streptomycin, while 90% of Irish-1 isolates were resistant to all these plus gentamicin and mupirocin. All isolates were sensitive to quinupristin/dalfopristin, teicoplanin and vancomycin. Urease production was negative in both strains. The results suggest that Irish-1 and Irish-2 are distinct epidemic strains, identifiable by phage typing, DNA profiles, antibiotic resistance and toxin gene carriage.     

Application of pulsed-field gel electrophoresis to the epidemiological characterization of Staphylococcus intermedius implicated in a food-related outbreak.

An outbreak of food intoxication involving over 265 cases in western United States occurred in October 1991. Staphylococcus intermedius was implicated as the aetiologic agent. Representative outbreak isolates (five clinical and ten from foods) produced type A enterotoxin. DNA fragments generated by four restriction endonucleases and analysed by pulsed-field gel electrophoresis (PFGE) provided definitive evidence that all isolates from nine different counties in California and Nevada were derived from a single strain. The PFGE pattern of these outbreak isolates was distinct from those of a heterogeneous collection of seven S. intermedius strains of veterinary origin and five unrelated S. aureus laboratory strains. The data show a significant PFGE pattern heterogeneity not only among members of different Staphylococcus species but also within members of the same species and even the same enterotoxin type. The results indicate that PFGE is a valuable strain-specific discriminator for the epidemiological characterization of S. intermedius. To our knowledge, this represents the first documented foodborne outbreak caused by S. intermedius. These findings suggest that the presence of S. intermedius and other species such as S. hyicus in food should be reason for concern.