High prevalence of CTX-M-type beta-lactamase in Escherichia coli isolates producing extended-spectrum beta-lactamase (ESBL) and displaying antibiotic co-resistance

In the present study, we investigated the prevalence of CTX-M-type beta-lactamase in extended spectrum beta-lactamase (ESBL)-producing Escherichia coli isolated in our hospital as well as their antibiotic resistance and co-resistance rates. Two hundred nineteen E. coli isolated from clinical specimens between 2006 and 2007 were included. Antibiotic susceptibility test was performed using disc diffusion method and ESBL production was determined using a double-disc synergy test. The presence of CTX-M-type beta-lactamase genes was investigated through amplification using specific primers. The prevalence of CTX-M-type beta-lactamase was found 87% in E. coli isolates. The isolates displayed high rates of resistance to tested antibiotics: 87% to ampicillin-sulbactam (SAM), 77% to amoxicillin-clavulanic acid (AMC), 76% to co-trimoxazole (SXT), 70% to norfloxacin (NOR), 68% to ciprofloxacin (CIP), and 51% to gentamicin (GN). All isolates were found susceptible to imipenem (IPM), meropenem (MEM) and fosfomycin (FOS). Co-resistance was identified in 96% of isolates, and the most common two co-resistance phenotypes were AMC/SAM/GN/NOR/CIP/SXT (12%) and AMC/SAM/NOR/CIP/SXT (11%). CTX-M-type beta-lactamase was present in E. coli isolates at extremely high rates. The empiric therapy with SAM, AMC, SXT, NOR, CIP, and GN may not be adequately effective against certain isolates of E. coli due to high rate of resistance.