Characterization of Dicloxacillin resistant mutants obtained from Listeria monocytogenes ATCC 15313

GUTKIND G; MOLLERACH M; OGUETA A; DE URTIAGA A; DE TORRES RA

Houston, Texas

Congreso; 29th Interscience Conference on Antimicrobial Agents and Chemotherapy; 1989

American Society for Microbiology

Dicloxacillin resistant mutants were isolated by selection techniques from Listeria monocytogenes ATCC 15313. The resistant strains exhibited also some degree of cross-resistance to other Beta-lactamic drugs. These strains did not show any morphological alteration when they were grown in the presence of inhibitory or sub-inhibiroty concentrations of Penicillin G, but were substantially filamentous in the presence of sub-inhibitory concentrations of Dicloxacillin, leading to the formation of helical filaments. Some of these mutants exhibited alterations in the affinity of PBPs 3-4 to Dicloxacillin without affecting the rate of binding of the radioactive penicillin, while others lacked PBPs, which could not be detected in direct binding studies. Also, another group of mutants presented the appearence of an extra PBP, of very low molecular weight. PBP 5 is completelly resistant to Dicloxacillin, while PBP 1 could not be detected in classical precompetence studies due to it's low affinity for the radiotracer.