基于ESBLs的食源性沙门氏菌耐药性传播和产生机制

Salmonella is one of the most common and harmful foodborne pathogens associated with food safety and consumer's health. The emergence of extended spectrum β-lactamases (ESBLs) has made many bacteria resist to cephalosporins, more worsely, the transmission of their encoding genes among the whole food production and supply chains as well as environment through corresponding vehicles resulted in more and more bacteria produced resistance. The increasing emergence of ESBLs producing Salmonella now has been a new threaten to food and public health safety. However, study on the mechanism of antibiotic resistance transmission and emergence associated with ESBLs in foodborne Salmonella was rare. In this study, foodborne ESBLs producing Salmonella isolates were used to 1) investigate the predominant genotypes of ESBLs, 2) clarify the situation of multidrug resistance transmission and emergence via conjugation in different media (culture medium, food, mice intestines), 3) seek the intimate gene islands and/or gene units associated with ESBLs encoding genes and antibiotic resistance transmission, to reveal the new mechanism of emergence and transmission of antibiotic resistance associated with ESBLs. Our results could further enrich the mechanism of antimicrobial resistance, and provide some directions to multidrug resistance prevention and transmission among foodborne pathogens, to ensure food safety and public health security.

沙门氏菌（Salmonella）是食品中最常见、对食品安全和消费者健康危害最大的食源性病原菌之一。超广谱β-内酰胺酶（Extended Spectrum β-lactamases, ESBLs）的产生可使细菌对头孢菌素耐药，且其编码基因可通过相应载体在食品全产业链、供应链及环境中扩散，导致更多细菌产生耐药性。不断涌现的产ESBLs沙门氏菌已成为新的食品和公共卫生安全威胁，但目前基于ESBLs的食源性沙门氏菌耐药性传播和产生机制知之甚少。本研究以产ESBLs多重耐药食源性沙门氏菌为材料，阐明其主要的ESBLs基因型及其通过接合方式在不同基质中传播多重耐药性的水平，挖掘与ESBLs编码基因“共转移”传播耐药性的固有基因岛和基因单元，揭示基于ESBLs的沙门氏菌多重耐药性传播和产生机制。研究结果可丰富细菌的耐药机制，为预防食源性致病菌多重耐药性出现和传播、保障食品和公共卫生安全提供理论参考。

分别以收集和分离自我国9个省市的3000余株食源性沙门氏菌为材料，使用双纸片扩散法筛选出产超广谱β-内酰胺酶（Extended Spectrum β-lactmases，ESBLs）的菌株，并对其进行基因型测定和验证，揭示产ESBLs沙门氏菌在食品中的流行状况及相关分子流行病学特性。以产CTX-M-55型ESBLs的沙门氏菌为材料，研究了肠杆菌科细菌中质粒介导的CTX-M-55型ESBLs耐药性传播机制；以产ESBLs沙门氏菌为材料，分别研究了携带TEM-1型、TEM-1b型和CTX-M-55型ESBLs编码基因沙门氏菌在小鼠肠道定植及其质粒介导的耐药性传播特性，在食品基质传播ESBLs编码基因的水平及质粒介导的耐药性；以同时携带ESBLs编码基因和mcr-1基因的沙门氏菌及大肠杆菌为材料，研究了mcr-1共存ESBLs编码基因的质粒的流行水平、在食品基质和小鼠肠道中质粒介导的耐药性传播机制。结果表明，产ESBLs沙门氏菌在我国零售食品中流行广泛，对多种抗生素协同耐药；CTX-M-55和TEM-1型ESBLs为主要流行的亚型；ESBLs编码基因多与其他抗生素耐药基因共存于质粒之上，ESBLs阳性菌株在体外（培养基）、食品基质和小鼠肠道内均可与其他菌株及小鼠肠道的固有菌接合并转移耐药基因，转播耐药性。转座子、接合质粒、插入序列等均可促使耐药基因和耐药基因盒在不同细菌间转移，且会在接合过程形成较大的融合质粒，这些融合质粒再进一步通过接合的方式传播耐药基因和耐药性。比较系统的阐明了产ESBLs沙门氏菌耐药性产生和传播机制，丰富了食源性致病菌耐药机制，可为国内外食品安全控制、防止细菌耐药性进一步扩散和增加提供理论基础。项目培养研究生6人，青年教师2名；资助参加与研究相关的国际学术会议2次，共12人次。发表科研论文14篇，其中SCI 7篇，中文7篇。