Antibiotic resistance of Escherichia coli isolates producing CTX-M extended spectrum β-lactamases

Objective To understand the antibiotic resistance of Escherichia coli isolates producing CTX-M type extended spectrum beta-lactamases(ESBLs).Methods 151 ESBLs-producing Escherichia coli isolates were detected by phennotyic confirmatory test. Polymerase chain reaction(PCR) were used to detect CTX-M genes. Minimal inhibitory concentrations(MIC) of 11 antibiotic for all ESBLs-producing isolates were determined by the agar dilution method according to the guidelines of the NCCLS. Results 139 of 151 ESBLs-producing Escherichia coli strains were found carrying CTX-M gene. Of all CTX-M type strains, 100% were susceptible to imipenem(MIC_(90)=0.25 μg/ml), 92.1% to amikacin, 90.6% to piperacillin/tazobactam and 65.8% to cefoxitin. Their susceptibility to ciprofloxacin Ampicillin/Sulbactam were very low(20.9% and 0% respectively). Conclusion Most of the ESBLs produced by Escherichia coli isolates were CTX-M in our area. Imipenem, amikacin and piperacillin/tazobactam have greater activity against Escherichia coli producing CTX-M, whereas ampicillin/sulbactam didn't show any activity against these bacteria.