INVESTIGADORES
MOLLERACH Marta Eugenia
congresos y reuniones científicas
Título:
ß-lactamases in Morganella morganii: Characterization of extended spectrum ß-lactamases
Autor/es:
POWER P; RADICE M; BARBERIS C; DE MIER C; MOLLERACH M; MALTAGLIATTI C; VAY C; FAMIGLIETTI A; GUTKIND G
Lugar:
Atlanta, USA
Reunión:
Congreso; 98th General Meeting of the American Society for Microbiology; 1998
Institución organizadora:
American Society for Microbiology
Resumen:
Antimicrobial susceptibility, both for ß-lactam and non ß-lactam antibiotic was determined on 29 Morganella morganii strains. Three groups could be defined according to ceftriaxone MICs. Preliminary detection of extended spectrum ß-lactamases (ESBL) and induction of chromosomal ß-lactamases were analyzed by double disk tests. ß-lactamases were assayed on crude extracts obtained from overnight cultures in the presence or absence of ß-lactamase inductor (30 ug/ml cephalotin). Nitrocefin hydrolysis, isoelectricfocusing (IEF) and SDS-PAGE revealed by an iodometric method using 500 ug/ml ampicillin or 1000 ug/ml ceftriaxone were performed. Characterization of the ESBL was complemented by partial sequencing and restriction patterns of PCR-amplified fragments using specific primers. Ten microorganisms (named group 1) highly susceptible (MIC <0.032 ug/ml) were only active on nitrocefin after induction with cephalotin; however, no detectable bands were observed by IEF or SDS-PAGE. Thirteen strains (group 3), whose ceftriaxione MICs were bellow NCCLS breakpoints but clearly higher than the first group, showed the presence of two enzymes active against ampicillin with apparent isoelectric points (pIs) of 6.4 and 7.4, with molecular weights of 23,000 and 36,000 respectively. The latter was only detectable in extracts obtained after induction (and not inhibited by clavulanate). In this group no good correlation was observed between the double disk test and actual presence of ESBLs or inducibility. The remaining six strains (group 2) were highly resistant to ceftriaxone (MICs >64 ug/ml). Presence of two ß-lactamases was demonstrated, with apparent pIs of 5.8 and 8.2 using ampicillin as substrate. Clavulanate and sulbactam inhibited both enzymes (apparent MW 23,000), but not by EDTA. The pI 8.2 enzyme was also active on ceftriaxone. This ESBL could be identified as CTX-M-derived enzyme by PCR restriction pattern and partial sequencing being the first ESBL of this kind in Morganella morganii