Dissemination of CTX-M-Type Beta-lactamase Among Clinical Isolates of Enterobacteriaceae in Markazi Province, Iran

Background: Organisms producing CTX-M -lactamases are known as the source of resistance to Oxyiminocephalosporins such as Eeftriaxone and Ceftazidime. However, the laboratory detection of these strains is not well defined. Objectives: The aim of this study was to determine the presence and prevalence of known CTX-M-beta- beta-lactamase genes in clinical isolates of Enterobacteriaceae from Arak educational hospitals, Iran. Materials and Methods: During a 10-month period (May to February 2010), 350 randomly Enterobacteriaceae isolates were obtained from the clinical laboratories of different hospitals of Arak University of Medical Sciences, Iran. Antibiotic susceptibility was tested by CLSI disk diffusion and extended spectrum beta-lactamase (ESBL) confirmatory tests. Minimum Inhibitory Concentration (MICs) was determined by broth micro dilution. All of the ESBL-producing isolates were examined by PCR to detect the presence of bla CTX-M genes. Results: In phenotypic confirmatory test, 154 (44%) out of 350 clinical isolates were ESBL positive. Using molecular assay, 154 strains potentially producing extended-spectrum-beta -lactamases were examined for the presence of CTX-M enzymes. 92.2% isolates CTX-M - 1, 28.5% isolates CTX-M-2, 17.5% isolates CTX-M-8, and 38.3% isolates CTX-M-9 genes detected by PCR. Conclusions: The levels of resistance to Ceftazidime were remarkably variable among CTX-Mproducers. This study provides further evidences of the global dissemination of CTX-M type ESBLs and emphasized on the need for their epidemiological monitoring.