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。

Antimicrobial susceptibility and SCCmec typing of methicillin-resistant Staphylococcus aureus isolates from swine

The purpose of the present study is to investigate the antimicrobial resistance and SCCmec typing of methicillin-resistant Staphylococcus aureus (MRSA) isolates from swine in Shanghai areas. A total of 232 samples of swine nasal swabs were collected from 5 swine farms and 1 slaughterhouse in Shanghai areas. Staphylococcus aureus were isolated by using 7.5% sodium chloride broth and CHROM agar. And MRSA isolates were identified by duplex PCR with nuc gene and mecA gene. Minimum inhibitory concentrations (MICs) of multiple antibiotics were measured by broth dilution method and the genotypes of these MRSA strains were analyzed by staphylococcal cassette chromosome mec (SCCmec). Results showed that a total of 139 S. aureus were isolated, and 70 strains were identified for MRSA and positive rate was 30.2% (70/232). These MRSA isolates were determined to be SCCmecⅣb type and no PVL gene was detected. All of the MRSA isolates were susceptible to Linezolid, Vancomycin and Amikacin. And 100% of these strains were resistant to Azithromycin, Erythromycin, Chloramphenicol, Florfenicol and Oxacillin. The resistance rates of Ceftiofur, Gentamicin and Norfloxacin were 74.3%, 62.9% and 42.9%, respectively. Interestingly, all the MRSA isolates were resistant to pleuromutilin antibiotics (Tiamulin, Valnemulin and Retapamulin). The results indicated that swine MRSA were SCCmecⅣb and were multidrug-resistant strains in Shanghai areas, especially, all of the MRSA isolates were resistant to pleuromutilin antibiotics (Retapamulin). These results also suggest that we should prevent the potential transition of resistant strains or resistant genes from animal to human, which could be through the food chains or the environment.