Survey of CTX-M Gene Frequency in Extended-Spectrum Beta-Lactamase-Producing Enterobacteriaceae Isolates Using the Combination Disk and PCR Methods in Ahvaz, Iran

BACKGROUND A common mechanism of resistance to beta-lactam antibiotics is the production of beta-lactamase by Gram-negative bacteria. Recently, nonderivative extended-spectrum beta-lactamases (ESBLs) from the TEM and SHV enzymes, such as CTX-M, that were related to different geographical regions have been recognized. OBJECTIVES The aim of this study was to determine the frequency of the CTX-M gene in ESBL-producing Enterobacteriaceae isolates in hospitalized patients in the teaching hospitals of Ahvaz, Iran. METHODS Enterobacteriaceae isolates from clinical specimens (other than stool), such as wounds, blood, urine, trachea, discharge, and abscess, were collected and examined. All the isolates were identified using standard biochemical tests. The combination test was carried out based on CLSI criteria for the phenotypic detection of ESBL-producing isolates. After DNA extraction, the CTX-M and CTX-M-1 genes were amplified using PCR among phenotypically positive ESBL isolates. RESULTS Among 240 Enterobacteriaceae isolates, Escherichia coli and Enterobacter were the most common isolates with 171 (71.3%) and 65 (27.1%), respectively. The combination test results also showed that 108 (45%) Enterobacteriaceae isolates were phenotypic ESBL producers, but 104 (96%) isolates were positive for the blaCTX-M gene and 99 (92%) were positive for the blaCTX-M-1 gene according to the PCR method. CONCLUSIONS The results of this study phenotypically and genotypically confirmed the high frequency of ESBL-producing strains, such as the CTX-M and CTX-M-1 genes, among Enterobacteriaceae isolates in our region. Therefore, use of antibiotic susceptibility testing for the detection of ESBL isolates prior to the prescription of beta-lactam antibiotics is recommended. This could help prevent the spread of bacteria strains that are resistant to beta-lactam antibiotics.