大肠埃希菌中共存两种携带ampC和/或超广谱β-内酰胺酶基因的质粒

Coexistance of two transferable plasmids-encoding ampC and/or ESBLs in one E.coli cell

目的：探讨从临床分离的大肠埃希菌（E．coli）中，由质粒编码的ampC和／或超广谱β-内酰胺酶（ESBLs）的基因质粒携带方式。方法：三维实验证实产AmpC酶的42株E．coli，用E．coliC600作为接合受体菌，采用头孢曲松和头孢他啶／头孢噻肟／棒酸两步淘筛法，进行对第三代头孢菌素耐药性的传递实验：用PCR法扩增质粒编码的ampC和ESBLs基因、三维酶实验和抗生素敏感实验对供体菌和接合子进行对比。结果：接合实验显示，有37侏供体菌对第三代头孢菌素的耐药性可传递，传递频率为10^-7～10^-5。其中23株菌仅传递了ESBLs耐药性，3株菌仅传递AmpC耐药性，11株菌传递了AmpC／ESBLs两种耐药性11株菌中，7株菌的AmpC／ESBLs耐药性携带在同一质粒上；另有4株菌各得到两种接合子，其中2株均得到携带ESBL耐药性和AmpC／ESBLs耐药性的2类接合子，2株均得到携带AmpC耐药性和ESBL耐药性的2类接合子结论：在同时表达AmpC和ESBLs两种酶的E．coli中，有些菌不能通过接合传递实验将两种耐药性分开传递，有些可分开传递。当AmpC和／或ESBLs耐药性基因在同一细菌中南2个质粒携带时，可在接合实验中得到两种不同的接合子。

Objective ：To determine the genetic forms of plasmids-encoding ampC and/or extended spertrum β lactamases （ESBLs） in isolates of E. coll. Methods ： Forty-two isolates of E. coli classified as AmpC β-lactamase producers according to the three-dimensional test were collected. The transferability of the third generation cephalosporins resistances was tested in broth mating experiments using an E. coli C600 recipient and CRO and CAZ/CTX/CA for selection of transconjugants. Donors and transconjugants were compared with PCR amplification of plasmid-encoded ampC and ESBLs genes, three-dimensional extract patterns and antimicrobial susceptibility testing. Results：These experiments showed that the resistant determinants for the third generation cephalosporins were transferable from 37 donors at the frequency of approximately 10^-7to 10^-5 transconjugants/recipient, while ESBLs determinants alone were transferable from 23 donors, AmpC determinants alone were from 3 donors, both AmpC and ESBLs determinants were from 11 donors. Among these 11 strains, AmpC/ESBLs determinants carried on one plasmid were from 7 donors, transconjugants derived from the other 4 donors each showed 2 types, 2 donors each derived both ESBLs-producing transconjugant and AmpC/ESBLs-producing transconjugant and theother 2 donors each derived both ESBLs-producing transconjugant and AmpC-producing transconjugant. Conclusion.The coexisting ESBLs-and ampC-enzymes in some E. coli could not be separated by conjugation experiments, while some could be separated when two transferable ampC-and/or ESBLs-encoding plasmids coexisted in one cell.