Study on plasmid-mediated extended spectrum β-lactamases and their resistance phenotypes in Shigella / 中华检验医学杂志

ABSTRACT

Objective To discuss the characteristics of extended-spectrum beta-lactamases(ESBLs)-producing Shigella and the relation between them and drug-resistance plasmid. Methods The suspicious ESBLs-producing isolates were screened by K-B disc diffusion method, and the ESBLs-producing strains were confirmed by confirmatory test recommended by the National Committee for Clinical Laboratory Standards. Furthermore, the partial blageneof these isolates were detected by PCR using universal primers for TEM, SHV, CTX-M-1 group, CTX-M-2 group and CTX-M-9 group, respectively. The entire blaCTX-M-9 and blaTEM were amplified by PCR using the primers outside the open reading frame (ORF) of these β-1actamases and products were directly sequenced. The conjugation experiment was performed to determine whether the resistance was transferable. Minimal inhibitory concentration (MIC) was detected with double agar dilution method. Results Of the 275 isolates, 12 strains were identified as ESBLs producers. Among them, 8 strains were CTX-M-14 carriers and 4 strains were CTX-M-3 carriers. All ESBLs-producing isolates are positive for plasmid conjugative transfer test. The transconjugants are only resistance to betalactams. Conclusions High resistance to beta-laetams in Shigella is caused by production of ESBLs in the local area. The ESBLs-produeing isolates can transfer the drug resistance through lateral transfer of plasmid.