MOLLERACH Marta Eugenia
congresos y reuniones científicas
ESBLsdetection : comparative analysis of different methods in an area with uncommon resistance markers.
QUINTEROS M; MOLLERACH M; RADICE M; MATTEO M; POWER P; DI CONZA J; CUDMANI N.; DURANTE G; ECHEVERRÍA A; COUTO E.,; GUTKIND G
San Francisco, USA
Congreso; 39th International Congress on Antimicrobial Agents and Chemoptherapy; 1999
American Society for Microbiology
Seventy-two ESBL producing enterobacteria from different regions of our country were used for comparing detection abilities of the NCCLS recently recommended methods for E. coli, K. pneumoniae and K. oxytoca (screening and phenotypic confirmation) with the use of a single ceftazidime (CAZ) 5 ug disk. We included clinical isolates of E. coli (n=30), Salmonella Infantis (n=11), P. mirabilis (n=6), S. sonnei (n=1), and K. pneumoniae (n=24), previously characterized as resistant to cefotaxime (CTX) by disk diffusion tests. B-Lactamase production was analyzed by isoelectrofocusing, and codifying genes for the enzymes confirmed by colony blot hybridization. We compared the following methods: (I) Agar dilution with CTX and ceftazidime (CAZ), alone and in presence of 4 ug/ml clavulanic acid (CLA); (II) Disk diffusion with standard concentrations of CAZ and CTX, using the new NCCLS g CAZ (susceptiblembreakpoints; (III) Disk diffusion with 5 >22 mm); (IV) Disk diffusion with CTX/CLA (30/10 ug) and CAZ/CLA (30/10 ug), compared with the inhibition zones for CTX and CAZ, respectively. Resistance was successfully detected (100 %) both by CTX agar dilution and diffusion, but only in two thirds of the isolates by the recommended CAZ breakpoints. The same results could be observed using the 5 mm increase by CLA. All (except forone P. mirabilis) displayed inhibition zones >21 mm using the CAZ 5 ug disk. As expected, those methods using CTX were more appropriate for detection of ESBL in our country due to widespread of CTX M-2 (with very poor hydrolytic activity on CAZ). However, use of a 5 ug CAZ disk improved detection of resistance in microorganisms harboring these enzymes, except in a single P. mirabilis, possibly due to low level production.