Beta-lactam antibiotic resistant genes and genotypes of escherichia coli from clinical specimens

Abstract

Thirty-seven extended spectrum beta-lactamase (ESBL) producing strains were detected among the 120 E. coli isolated from blood, pus, and urine of the patients at Siriraj Hospital during June to August 2004 using the National Committee for Clinical Laboratory Standards (NCCLS) initial screen test and the phenotypic confirmatory test. Antimicrobial susceptibility test of all ESBL producing E. coli strains were performed. Among the third generation cephalosporins, it was shown that all strains were resistant to cefpodoxime while these strains were more susceptible to ceftazidime (46.0%) than to cefotaxime (8.1%) and ceftriaxone (5.4%). For the other beta-lactam antibiotics, it was shown that 2.7% were susceptible to ampicillin, 10.8% to amoxicillin/clavulanic acid, 2.7% to cefazolin, 67.6% to cefoxitin, 19.0% to aztreonam, and 97.3% to imipenem. For non beta-lactam antibiotics, it was shown that 13.5% were susceptible to gentamicin, 32.4% to norfloxacin, and 27.0% to trimethoprim /sulfamethoxazole. The purified DNA from ESBL producing strains were also subjected for polymerase chain reaction (PCR) amplification of ESBL genes (bla [subscript TEM], bla [subscript SHV], bla[subscript CTX-M], and bla [subscript VEB] genes). Among 37 ESBL producing E. coli strains, 78.4% were bla [subscript TEM] positive, 8.1% were bla [subscript SHV] positive, 78.4% were bla [subscript CTX-M] positive, 8.1% were bla [subscript VEB] positive, and 75.7% were coharboured at least 2 different bla genes. As a result, the presence of bla [subscript TEM] and bla [subscript CTX-M] in ESBL producing E. coli strains indicates the high prevalence of these genes. All 120 E. coli strains were investigated for the presence of an integrase (intI1) gene which acts as the antimicrobial resistant genes carries to the other bacterial strains by PCR. Southern blot analysis using intI1 as a probe was also performed for all isolated DNA. As a result, as high as 99.2% of the strains carried intI1. This indicated the wild spread of resistant bacteria in Siriraj Hospital. There were 32 different pulsotypes among all 37 ESBL producing E. coli strains. The various different types indicated that horizontal gene transfer was more predominate than vertical gene transfer for the mode of antibiotic resistance transmission.