Transposition of ISEcp1 modulates blaCTX-M-55-mediated Shigella flexneri resistance to cefalothin

• Published in: International journal of antimicrobial agents Vol. 42; no. 6; pp. 507 - 512
• Main Authors: Wang, Yingfang, Song, Chunhua, Duan, Guangcai, Zhu, Jingyuan, Yang, Haiyan, Xi, Yuanlin, Fan, Qingtang
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.12.2013
• Subjects: Anti-Bacterial Agents - pharmacology; beta-Lactam Resistance; beta-lactamase; beta-Lactamases - genetics; blaCTX-M-55; cefazolin; Cephalothin - pharmacology; DNA Transposable Elements; DNA, Bacterial - chemistry; DNA, Bacterial - genetics; Escherichia coli; Escherichia coli - drug effects; Escherichia coli - genetics; Extended-spectrum β-lactamase; Gene Expression Regulation, Bacterial; ISEcp1; minimum inhibitory concentration; Molecular Sequence Data; plasmids; Recombination, Genetic; reverse transcriptase polymerase chain reaction; Sequence Analysis, DNA; Shigella flexneri; Shigella flexneri - drug effects; Shigella flexneri - genetics; blaCTX-M-55; ISEcp1; Extended-spectrum β-lactamase; bla(CTX-M-55)
• ISSN: 0924-8579; 1872-7913
• DOI: 10.1016/j.ijantimicag.2013.08.009

The aim of this study was to uncover the mechanisms underlying Shigella flexneri resistance to cefalothin. In this study, a resistance-related S. flexneri isolate, S. flexneri YDC, was obtained from S. flexneri mel-1998023/zz pre-incubated with cefalothin at a dose of 0.5× the minimum inhibitory concentration. The ISEcp1 coding element was identified upstream of blaCTX-M-55 in S. flexneri YDC. To further determine the role of ISEcp1 in S. flexneri resistance, plasmids containing blaCTX-M-55 recombinant with or without the ISEcp1 sequence were constructed and named as pCTX and pISECTX, respectively. It was shown that Escherichia coli DH5α(pISECTX) was resistant to all β-lactams tested. In contrast, E. coli DH5α(pCTX) was sensitive to all except β-lactams cefazolin and cefalothin. In addition, reverse transcription PCR showed that expression levels of blaCTX-M-55 were higher in E. coli DH5α(pISECTX). The Clinical and Laboratory Standards Institute (CLSI) assay demonstrated that extended-spectrum β-lactamase was only positively detected in E. coli DH5α(pISECTX) but not in E. coli DH5α(pCTX). Taken together, these results suggest that the translocated ISEcp1 element upstream of blaCTX-M-55 is required for overexpression of blaCTX-M-55, leading to cephalosporin resistance.