Antimicrobial Resistance, Class 1 Integrons and Extended-Spectrum β-Lactamases in Escherichia coli Clinical Isolates from Patients in South Thailand

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Five hundred and ninety seven Escherichia coli (E. coli) isolates were obtained from clinical specimens at the Songklanagarind Hospital in Songkhla Province, Thailand during 2003-2005. Antimicrobial susceptibilities to ten antimicrobial agents were tested by a standard disk diffusion method. The presence of class 1 integrons was based on the detection of the integrase gene (intI1) by PCR. Extended-spectrum β-lactamases (ESBLs) were detected by a combination disk method. The highest percentage of resistance was found to ciprofloxacin (40.5%), norfloxacin (39.0%), and cefuroxime (33.2%). The IntI1 was detected in 59.5% of the tested isolates. Resistance to gentamicin, cefazolin, cefuroxime, cefotaxime, ceftriaxone, norfloxacin, and ciprofloxacin was significantly higher in class 1 integron-positive isolates (p<0.05). The most prominent resistance pattern was for norfloxacin-ciprofloxacin (17.7%). ESBLs were detected in 75 out of 597 (12.6%) isolates; 56/302 (18.5%) and 19/295 (6.4%) were from hospitalized and non-hospitalized patients, respectively. Seventy-five percent of ESBL-positive strains were integron-positive isolates. Imipenem and meropenem were still able to inhibit all ESBL-producing strains. The results indicated that class 1 integrons are widely prevalent among clinical isolates of resistant E. coli especially in ESBL-producers and are probably a reservoir for producing multidrug resistance and nosocomial infections in hospitals.