Objective: To analyses the antimicrobial resistance and molecular characterization of 21 MRSA isolates cultured from retail foods from different provinces in China, and evaluate the molecular typing methods. Methods: Twenty-one MRSA isolates were obtained from national foodborne pathogen surveillance network in 2012 (Chinese salad, n=3; milk, n=1; cake, n=2; rice, n=1; cold noodle, n=1; spiced beef, n=1; dumpling, n=1; packed meal, n=1; salad, n=1; raw pork, n=9). The antimicrobial resistance of 21 strains to 12 antimicrobial agents was tested by broth dilution method. Polymerase chain reaction (PCR) and DNA sequencing were performed to obtain the genetic types of MLST (ST) and spa typing. The clonal complex (CC) was assigned by eBURST soft and the MLVA type (MT) and MLVA complex (MC) were identified via the database of the MLVA website (http://www.mlva.net). SmaI pulsed-field gel electrophoresis (SmaⅠ-PFGE) was also carried out to obtain the PFGE patterns of 21 strains. The genetic diversity and discriminatory power of typing were calculated by the Simpson's index of diversity (diversity index, DI) to find out the best genotyping method for MRSA. Results: All MRSA isolates showed multi-drug resistance(MDR), and were resistant to oxacillin, benzylpenicillin, clindamycin and erythromycin, and 71.4% (15/21), 47.6% (10/21), 42.9% (9/21) and 28.6% (6/21) of the MRSA isolates were resistant to tetracycline, ciprofloxacin, trimethoprim/sulfamethoxazole and gentamicin, respectively. Moreover, one strain was found to be resistant to all three antimicrobials of levofloxacin, moxifloxacin and rifampicin. Great diversity was found in these food-associated MRSA (6 STs, 7 spa types, and 9 MTs). PFGE patterns were more diverse than those of other three molecular typing methods (19 pulse types). The index of diversity (DI) of PFGE, MLVA, spa typing and MLST was 0.99, 0.80, 0.73, and 0.61, respectively. Among the MRSA isolates, CC9-ST9-t899-MT929-MC2236 (PFGE Cluster Ⅴ) was the most prevalent clone, which were all cultured from raw pork (9 isolates). Besides, two MRSA were identified as CC59-ST338-t437-MT621-MC621 (PFGE Cluster Ⅳ). Different clone had their own resistance spectrum profiles. Conclusion: The food-borne MRSA isolates were all MDR in this study. Different clones had their own resistance spectrum profiles. MLVA represented a promising tool for molecular epidemiology tracing of MRSA in foodborne disease events.
目的： 分析食源性耐甲氧西林金黄色葡萄球菌（MRSA）对常用抗生素的耐药情况及分子分型特征，并评价分子分型方法。 方法： 21株MRSA菌株来自2012年全国污染物监测网（凉拌菜分离3株，牛奶分离1株，糕点分离2株，米饭分离1株，凉面分离1株，酱牛肉分离1株，水饺分离1株，盒饭分离1株，沙拉分离1株，生猪肉9株），采用微量肉汤稀释法测定菌株对11种抗生素的耐药性，并采用PCR方法对菌株进行扩增，获得多位点序列分型（MLST，ST型）、spa分型，通过eBURST软件获得克隆簇（CC），登陆http://www.mlva.net网站获得多位点可变数目串联重复序列（MLVA，MT型）和MLVA复合体（MC）；采用SmaⅠ-PFGE获得菌株的PFGE带型；应用Simpson区分系数（DI值），评价各方法的分型能力，以发现适合MSRA最强分辨率的分型方法。 结果： 所有MRSA菌株均为多重耐药株（耐3类及以上抗生素），对苯唑西林、苄青霉素、克林霉素和红霉素均耐药，对四环素、环丙沙星、磺胺甲噁唑/甲氧苄啶和庆大霉素的耐药率分别为71.4%（15株）、47.6%（10株）、42.9%（9株）和28.6%（6株），此外有1株菌对左氧氟沙星、莫西沙星和利福平均耐药。21株菌株可分为6种ST型、7种spa型、9个MLVA型和19个PFGE带型，PFGE、MLVA、spa及MLST分型方法的DI值依次为0.99、0.80、0.73和0.61。分离自生猪肉的9株MRSA被识别为CC9-ST9-t899-MT929-MC2236，PFGE带型Ⅴ，为主要的MRSA流行克隆，此外，有2株MRSA被识别为CC59-ST338-t437-MT621-MC621，PFGE带型Ⅳ，不同的流行克隆具有特定的耐药谱。 结论： 食源性MRSA多重耐药普遍存在，不同流行克隆具有特定的耐药谱，MLVA可作为处理MRSA所致突食源性疾病的首选溯源分型工具。.
Keywords: Drug resident; Methicillin-resistant Staphylococcus aureus; Molecular typing; Raw pork.