血流感染患者金黄色葡萄球菌erm基因检测及流行病学研究

Detection of erm genes and epidemiology research of Staphylococcus aureus in patients with bloodstream infection

目的了解2006年1月至2011年8月临床血流感染患者红霉素耐药金黄色葡萄球菌红霉素核糖体甲基化酶(erm)基因分布特点及流行情况。方法收集2006年1月至2011年8月引起血流感染的39株红霉素耐药金黄色葡萄球菌。应用VITEK 2 Compact全自动细菌鉴定仪及配套鉴定卡、药物敏感性卡对细菌进行鉴定及药物敏感性试验。头孢西丁纸片扩散法筛选耐甲氧西林金黄色葡萄球菌(MRSA),并以D试验测定红霉素对克林霉素的诱导耐药表型。聚合酶链反应(PCR)分别检测ermA、ermB、ermC基因。脉冲场凝胶电泳(PFGE)和葡萄球菌染色体mec(SCCmec)分型方法了解产ermA金黄色葡萄球菌的流行情况。结果 39株红霉素耐药金黄色葡萄球菌对克林霉素、青霉素、庆大霉素的耐药率高,分别为100.0%、92.3%、53.8%。8株(20.5%)红霉素耐药而克林霉素敏感株D试验全部为阳性结果。erm基因的携带率为100.0%,ermA、ermB、ermC基因检出率分别为25.6%(10/39)、46.2%(18/39)、46.2%(18/39);红霉素对克林霉素诱导耐药株ermC基因携带率为75.0%(6/8),ermA基因携带率25.0%(2/8)。PFGE分型结果显示10株携带ermA基因的MRSA为6个不同克隆株,SCCmec分型结果显示8株为SCCmecⅢ型菌株,2株未能分型。结论在引起血流感染的红霉素耐药金黄色葡萄球菌中erm基因携带率高,ermA基因多分布于MRSA中,甲氧西林敏感金黄色葡萄球菌(MSSA)主要携带ermB基因,红霉素对克林霉素诱导耐药株主要携带ermC基因。携带ermA基因菌株全部为MRSA,主要是SCCmecⅢ型,对多种药物耐药,并存在散在克隆传播现象。

Objective To investigate the distribution and epidemic situation of erythromycin ribosome methylase （erm） genes in erythromycin-resistant Staphylococcus aureus in patients with bloodstream infection from January 2006 to August 2011. Methods A total of 39 isolates of erythromycin-resistant Staphylococcus aureus were collected from January 2006 to August 2011 among patients with bloodstream infection. The bacterium identification and antimicrobial susceptibility test were conducted by VITEK 2 Compact automatic system, matched identification card and antimicrobial susceptibility card. Methicillin-resistant Staphylococcus aureus （MRSA） was identified by disk diffusion method with cefoxitin. Phenotypic expression of inducible resistance was assessed by D test. Polymerase chain reaction （PCR） was used to detect ermA, ermB and ermC genes. The epidemic situation of ermA-producing Staphylococcus aureus was analyzed by pulsed-field gel electrophoresis （PFGE） and Staphylococcal cassette chromosome mec （SCCmec） typing. Results The resistant rates of 39 erythromycin-resistant Staphylococcus aureus to clindamycin,penicillin and gentamicin were high,and were 100.0% ,92.3% and 53.8% ,respectively. A total of 8（20.5% ） isolates of Staphylococcus aureus with discordant resistance pattern （erythromycin resistant and clindamycin sensitive） were all positive in D test. The positive rates of ermA,ermB and ermC were 25. 6% （10/39） ,46.2% （18/39） and 46.2% （ 18/39）, respectively. A total of 75.0% （6/8） and 25.0% （2/8） isolates with phenotypic expression of inducible resistance by D test harbored ermC and ermA genes. PFGE analysis of the all 10 MRSA isolates harboring ermA gene produced 6 distinct pulsotypes, 8 MRSA isolates were SCCmec m genotype, and 2 MRSA isolates could not be determined by SCCmec typing.Conclusions The positive rate of erm genes in erytbromycin-resistant Staphylococcus aureus in patients with bloodstream infection is relatively high. The ermA and ermB genes are mainly harbored by MRSA and methicillin-sensitive Staphylococcus aureus（MSSA）,respectively. The isolates with erythromycin inducible to clindamycin resistance mainly harbored ermC gene. A total of 10 isolates harboring ermA gene are all MRSA , and are muhidrug-resistant . There is scattered cloning spread of MRSA belonging to SCCmec III genotype with ermA gene.