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

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 beta-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.