Genotype and drug resistance of CTX-M extended spectrum beta-lactamases in clinical isolates of Shigella

Objective To understand the genotype and drug resistance of CTX-M extended spectrum beta-lactamases(ESBLs) in clinical isolates of Shigella in Xicheng district of Beijing. Methods Totally 83 strains of clinical isolates of Shigella were colleted in Xicheng district from 2008 to 2011. CTX-M ESBLs was detected by polymerase chain reaction(PCR), then the sequencing for PCR positive products was performed, the sequencing results were aligned with those in GenBank to determine gene subtypes, meanwhile the nucleotide sequence was analyzed by using DNAman software. The drug susceptibility test of the strains carrying CTX-M ESBLs gene to 8 kinds of cephalosporins was performed by Kirby-Bauer method. Results Among 83 strains of Shigella, 13(15.66%) carried CTX-M ESBLs gene. The results of DNA sequence analysis showed that CTX-M ESBLs were all CTX-M-14 subtype, and no single nucleotide polymorphism(SNPs) site was found. The results of drug susceptibility test showed that 13 strains carrying CTX-M ESBLs were resistant to cephalothin, cefazolin and cefotaxime. However, they were sensitive to cefoxitin, ceftazidime, cefepime and cefoperazone, but some strains were resistant to aztreonam. Conclusion The CTX-M ESBLs in Shigella isolated in Xicheng district of Beijing were mainly CTX-M-14 subtype and the gene structure was stable. The strains carrying CTX-M-14 ESBLs showed multidrug resistance.