食品动物源沙门菌fosA_3基因的流行及传播特征

Prevalence and dissemination of fosfomycin resistance gene fosA_3 among Salmonella isolates from food-producing animals

为研究质粒介导的磷霉素耐药基因fosA_3在食品动物源沙门菌中的流行状况及传播特征,采用PCR方法对本实验室保存的288株动物源沙门菌进行磷霉素耐药基因fosA_3、fosA和fosC2的检测,用琼脂稀释法测定阳性菌株对17种抗生素的敏感性,PCR检测其他相关耐药基因,玻片凝集法确定其血清型。采用脉冲场凝胶电泳(PFG E)和多位点序列分型(M LST)分析菌株间的亲缘关系。采用接合转移/转化、复制子分型、S1-PFGE和Southern杂交等对fosA_3的水平传播和质粒特征进行分析。结果显示,共筛选得到6株(2.1%)fosA_3阳性沙门菌,没有检测到fosA和fosC2。6株fosA_3阳性菌均表现出多重耐药,且同时携带blaCTX-M-9G(均为blaCTX-M-14)基因和floR基因,血清型检测均为印第安纳型。6株菌均为MLST(ST)17型,PFGE结果显示其图谱相似。质粒分析结果显示,fosA_3能通过IncN或IncA/C型质粒与blaCTX-M基因发生共同转移。本研究首次从国内不同地区采集的鸡粪便拭子样本中分离得到的沙门菌中检测到fosA_3基因,菌株的克隆传播和fosA_3与blaCTX-M随质粒的水平传播都加速了耐药性的散播,对公共卫生构成潜在威胁。

To investigate the prevalence and dissemination of plasmid-mediated fosfomycin resistance gene related to fosA3 among Salmonella isolates from food-producing animals in China,a total of 288 Salmonella isolates stored in our laboratory were used in this study.The presence fosfomycin resistance genes such as fosA3,fos A,and fosC2 and other associated resistance genes were screened by PCR.The susceptibility of fos-positive isolates to 17 kinds antimicrobial agents was performed by the ager dilution method,and serotypes were confirmed by slide agglutination. Pulsedfield gel electrophoresis（PFGE） and multi-locus sequence typing（MLST） were used to analyze the genetic relationship among strains.Plasmid analysis was carried out by conjugation, transformation,plasmid replicon type,S1-PFGE and Southern-blot.Six（2.1%） Salmonella isolates were positive for fosA3.None of the fos A or fosC2 was identified. All of these isolates were S.enterica serovar Indiana and presented multi-drug resistant phenotypes.Both blaCTX-M-9Gand flo R genes were detected in the fosA3 positive strains.MLST and PFGE results showed that all the 6 fosA3-harbouring Salmonella isolates belonged to MLST（ST） 17 and were clonally related.The result of plasmid analysis showed that fosA3 could be co-transferred with the blaCTX-Mgene through Inc Nor Inc A/C plasmids.The current study is the first report of the detection of fosA3 in Salmonella isolates from fecal swab samples among chickens in China.Both clonal spread of resistant strains and horizontal transmission of the resistance plasmids contributed to the dissemination of fosA3/blaCTX-M-9G-positive Salmonella isolates.It may pose a potential threat to public health.