Study on extended-spectrum β-lactamases and their genotypes of Shigella isolated from Tianjin / 中华传染病杂志

ABSTRACT

Objective To study genotypes,antibiotic resistance and epidemiology of extendedspectrum β-lactamases (ESBL)-producing Shigella isolated in Tianjin,and to discuss the relationship between ESBL-producing Shigella and drug-resistance plasmid.Methods A total of 136 Shigella spp.were isolated from stool specimens of patients with diarrhea who presented mainly with bloody purulent stool from Tianjin Children's Hospital,Tianjin Medical University No.2 Hospital and Tianjin No.1 Central Hospital between May 2009 and September 2010.Suspicious ESBL-producing isolates were screened by K-B disc diffusion method. The conjugation experiment was performed in the confirmed ESBL-producing strains and antibiotic resistance was compared between clinical strains and transconjugants to confirm the plasmid-mediated resistance. The genotypes of these isolates were detected by polymerase chain reaction (PCR) using universal primers for TEM,SHV,CTX-M-1 group,CTX-M-2 group,CTX-M-9 group,respectively.Intergenic consensus PCR (ERIC-PCR) was employed to understand the molecular homology of the ESBL-producing isolates. The data were analyzed by x2 test.ResultsESBL were identified in 14.7％ (20/136) of Shigella isolates,but no AmpC enzyme were detected.Among all the Shigella isolates,16 strains were genotype CTX-M-14,4 were genotype CTX-M-15.The strains with CTX-M ESBL were resistant to multiple antibiotics,while 100％ sensitive to imipenem.The transconjugant test of 18 ESBL-producing isolates were positive,and these conjugations were only resistant to β-lactamases. Conclusions CTX-M type is the common genotype of ESBL-producing Shigella isolates in Tianjin. ESBL-producing is the main cause of multiple resistance to β-lactams.The transmission of CTX-M producing strains is mainly mediated by plasmids.