[Detection of the phenotypes of resistance of enterobacteriaceae to aminoglycosides with ATB Plus Expert System]

Abstract

ATB Plus Expert (Biomérieux SA) is an expert system which has been developed to perform an interpretative reading of ATB susceptibility tests. The system was tested on the results obtained for 217 strains of enterobacteriaceae. These strains were selected in order to cover a maximum of bacterial species and resistance mechanisms. The isolates were tested on rapid ATB E, rapid ATB G-, rapid ATB Ur, ATB G- and ATB Ur strips. In parallel, a disc diffusion susceptibility test was performed with 5 discs of aminoglycosides (kanamycin, gentamicin, tobramycin, netilmicin, amikacin) and the interpretation was carried out according to the criteria usually followed. Of the 217 strains tested, 122 showed a resistance phenotype. Only the rapid ATB E strips included kanamycin and allowed the detection of APH(3') phenotypes. Amikacin was not included in the ATB Ur strip, consequently it was impossible to discriminate AAC(3)-II and AAC(6') + AAC(3)-I phenotypes. 12 strains did not grow within 5 hours using the rapid ATB methodology. Not taking into account the problems previously encountered, different phenotypes between the 6 susceptibility tests were found for 16 strains. In 5 cases the expert system detected an anomaly instead of the correct phenotype, and in 3 cases of unknown phenotypes, the answers were variable. In the other cases, the main difficulty was the detection of the isolated resistance to gentamicin (AAC(3)-I phenotype). The expert system automatically corrects the susceptibility test result according to the phenotype observed.