OBJECTIVES: This study aimed to determine the prevalence of extended spectrum of beta lactamases (ESBLs), to compare different phenotypic methods for ESBL confirmation and to evaluate the antibiotic resistance patterns among ESBL-producing urinary Escherichia coli. METHODS: Urinary E. coli isolates that were resistant to at least one of the three indicator cephalosporins (cefotaxime, cefpodoxime and ceftazidime) were tested for ESBL production using the double disc synergy test (DDST), the inhibitory potentiated disc diffusion (IPDD) test and the quantitative E-strip method. RESULT: Of the 163 E. coli strains isolated, 80 (49%) were resistant to at least one of the three cephalosporins, and 38 (47.5%) tested positive for ESBLs by the IPDD test and the E-strip test. However, only15 (18.7%) strains tested positive by the DDST. Among the third-generation cephalosporins, cefpodoxime (46.1%) was the best screening indicator, followed by ceftazidime (43%) and cefotaxime (39.9%). Most of the ESBL producers (97.3%) were resistant to three or more drugs, compared with 51.2% of non-ESBL producers. CONCLUSION: Compared with the DDST, the IPDD and E-strip tests appear to be preferable methods for detecting ESBLs, with better sensitivity (100%) and specificilty (97.6%) and positive predictive values (97.3%). ESBL producers showed significantly (p<0.05) higher resistance to tobramycin, co-amoxyclav and amikacin than did non-ESBL producers.
OBJECTIVES: This study aimed to determine the prevalence of extended spectrum of beta lactamases (ESBLs), to compare different phenotypic methods for ESBL confirmation and to evaluate the antibiotic resistance patterns among ESBL-producing urinary Escherichia coli. METHODS: Urinary E. coli isolates that were resistant to at least one of the three indicator cephalosporins (cefotaxime, cefpodoxime and ceftazidime) were tested for ESBL production using the double disc synergy test (DDST), the inhibitory potentiated disc diffusion (IPDD) test and the quantitative E-strip method. RESULT: Of the 163 E. coli strains isolated, 80 (49%) were resistant to at least one of the three cephalosporins, and 38 (47.5%) tested positive for ESBLs by the IPDD test and the E-strip test. However, only15 (18.7%) strains tested positive by the DDST. Among the third-generation cephalosporins, cefpodoxime (46.1%) was the best screening indicator, followed by ceftazidime (43%) and cefotaxime (39.9%). Most of the ESBL producers (97.3%) were resistant to three or more drugs, compared with 51.2% of non-ESBL producers. CONCLUSION: Compared with the DDST, the IPDD and E-strip tests appear to be preferable methods for detecting ESBLs, with better sensitivity (100%) and specificilty (97.6%) and positive predictive values (97.3%). ESBL producers showed significantly (p<0.05) higher resistance to tobramycin, co-amoxyclav and amikacin than did non-ESBL producers.