ISEcp1介导志贺菌头孢菌素抗生素耐药的分子机制研究

Objective To compare the location of ISEcp1 in Shigella flexneri before and after induced by Cephalothin(CF), and study the relationship between the CTX-M extended spectrum beta-lactamase expression. Methods Clinical shigella flexneri strain was induced into anti-drug strain by 1/2 MIC induced trails of CF. ISEcp1 and CTX-M were amplified by polymerase chain reaction(PCR) in original strain and induced anti-drug strain . PCR-mapping was used to detect blaCTX-M, ISEcp1 and analyze their relatioship. The PCR products were sequenced and compared. The complete blaCTX-M and the ISECTX included downstream of ISEcp1 and the complete blaCTX-M were inserted in a T-vector and transformed into DH-5α which were named DH5α(CTX) and DH5α(ISECTX). The expressing levels of blaCTX-M in DH5α(CTX) and DH5α(ISECTX) were detected by RT-PCR. Sususceptibility tests were performed in the two clones. Results Induced anti-drug strain of shigella flexneri was obtained successfully. It is resistant to cefalotin(CF) at a high level. ISEcp1 and blaCTX-M-55 were found in original strain and induced anti-drug strain . blaCTX-M-55 was flank upsream by an ISEcp1 element provide a right inverted repeat (IRR) recognized by transposase; -35 and -10 promoter sequences may drive the expression of blaCTX-M gene at a high level. The expressing levels of blaCTX-M in DH5α(ISECTX) was higher than DH5α(CTX). The antibiotic resistances of DH5α(ISECTX) to ceftotaxime(CTX), ceftriazone(CRO), cefurosimic sodium(CXM) and cefepime(FEP) were higher than DH5α(CTX). Conclusion ISEcp1 element could translocate upstream of blaCTX-M in S. flexneri following induction by cephalothin. ISEcp1 may drive the expression of the balCTX-M geng at a high level in Shigella spp.