Two methods for the detection of ESBL phenotypes

Abstract:

ObjectiveTo investigate antimicrobial resistance and genotypes of extendedspectrum βlactamases (ESBLs)producing strains isolated from clinic in a hospital, and to establish an effective method to analyze ESBL phenotypes.MethodsOne hundred ESBL positive isolates （initial screen test was positive） were randomly selected as experimental group, and 30 ESBL negative isolates （initial screen test was negative） was as control group. All strains were identified by Vitek2 Compact automatic system，and antimicrobial susceptibility test was performed by KirbyBauer disc diffusion method; Carbapenemresistant isolates were detected by modified Hodge test; βlactamase phenotypes were detected by both ESBL phenotypic confirmatory test recommended by Clinical Laboratory Standard Institute(CLSI) and modified ESBL confirmatory test incorporating 3aminophenylboronic acid; ESBL genes of all isolates were detected by PCR and DNA sequencing. ResultsESBL screen positive isolates were all resistant to cefotaxime, but susceptible to carbapenems; the modified Hodge tests were positive in two carbapenemresistant isolates. The detection rate of ESBL genes was 84.00%, the dominant genes were SHV and CTXM type. PCR detection for ESBL genes was regarded as a golden standard，and the sensitivity，specificity，negative predictive value, as well as positive predictive value of ESBL phenotype confirmatory test and modified ESBL phenotype confirmatory test was 72.61%, 100.00%, 100.00%, 66.67% and 98.81%，100.00%，100.00%, 97.87% respectively, the difference was significant (χ2=7.53, P=0.006). ConclusionESBL screen test positive isolates still have a high susceptible rate to carbapenems. ESBL phenotypes can be effectively detected by modified ESBL confirmatory test incorporating 3aminophenylboronic acid.