Investigation of beta lactamases genes and clonal relatedness among the extended-spectrum beta lactamase producing-nosocomial Escherichia coli isolates

Objective(s): Extended spectrum beta lactamase (ESBL) producing microorganisms are a global problem and especially CTX-M beta lactamase-producing Escherichia coli has disseminated worlwide as an important cause both nosocomial and community infections. The aim of this study was to assess the types and frequency of the beta lactamase genes and to investigate antibiotic susceptibility and clonal relationship in ESBL-producing hospital isolates of E. coli.Material and methods: A total of seventy-six extended-spectrum beta-lactamases (ESBLs) producing E. coli strains isolated from patients hospitalized at Inonu University Turgut Ozal Medical Center between June 2010-June 2011 were evaluated. Antibiotic susceptibilities of isolates were detected by Kirby Bauer disc diffusion method according to Clinical and Laboratory Standards Institute (CLSI). ESBL production was tested by double disc diffusion method. When ESBL production was indeterminate, cefotaxime/ cefotaxime-clavulanic acid E test strip (AB-Biodisk) was used. Existence of TEM, SHV, CTX-M, OXA-2 group, 0XA-10 group, PER, VEB and GES beta lactamase genes were investigated by polymerase chain reaction (PCR) method using primers spesific to these sites. Pulsed Field Gel Electrophoresis (PFGE) method was used for detection of clonal relationships between strains.Results: The frequence of ESBL-producing E. coli isolates were detected as 35% from intensive care unit, 16% from internal medicine and 13% from general surgery departments. These isolates were isolated 34% from urine, 33% from blood and 21% from wound specimens. All 76 strains were susceptible to imipenem, meropenem and amikacin. None of the isolates were susceptible to cefotaxime and ceftriaxone. The susceptibility of ESBL positive E. coli isolates to ertapenem was 83%, 61% to piperacillin/tazobactam, 63% to cefoperazone/sulbactam, 18% to ceftazidime, 25% to cefepime and 20% to aztreonam. The rates of CTX-M, TEM, OXA-2 group, PER, SHV, OXA-10 group beta lactamases were found as 89.5%, 59.2%, 15.8 %, 14.5%, 11.8% and 3.9% for E. coli strains, respectively. None of the isolates were positive for VEB and GES beta lactamases. All the beta lactamase genes were not detected in the only one isolate in the study. CTX-M beta lactamase gene was detected as alone in 20 isolates. The PCR analysis of the 25 isolate revealed that CTX-M coexited with TEM beta lactamase gene. The number of isolates containing only TEM type beta lactamase gene was found to be two. SHV beta lactamase gene was not found alone in any isolate. Pulsed-field gel electrophoresis analysis demonstrated that there was no major clonal relationship among these ESBL producing isolates.Conclusions: This study indicated that CTX-M type enzymes were highly endemic among ESBL-producing nosocomial E. coli strains in our hospital. The spread of ESBL-producing bacteria detected to be polyclonal and there was not dominant clone or epidemic clone. The resistance genes should be transferred by mobil genetic elements. However plasmid analyse and Multilocus sequence typing (MLST) have to perform for the relationship between epidemic clone and plasmids.Keywords: E. coli, beta lactamase genes, CTX-M, PFGE