In vivo Development of Beta-Lactam resistance by a Clinical Isolate of Enterococcus hirae

MASSA R; BANTAR C; MOLLERACH M; GUTKIND G

Banff, Canadá

Conferencia; 1st International ASM Conference on Enterococci: Pathogenesis, Biology, and Antibiotic Resistance.; 2000

American Society for Microbiology

An Enterococcus hirae isolate with decreased susceptibility to ß-lactams (EHR, penicillin MIC, 8 mg/l), emerged in vivo from a susceptible parental strain (EHS, penicillin MIC, £ 0.5 mg/l) during ampicillin treatment of a patient with a urinary tract infection. Both pre- and post-therapy urine specimens contained ñ 105 cfu/ml of E. hirae. A laboratory derived mutant (EHM) highly resistant to penicillin (MIC, 32 mg/l) was also easily selected from EHS and used for comparison, as E.hirae ATCC 9790 and E.hirae R40, ß-lactamases production was discarded by the chromogenic cephalosporin method. PBP5 overproduction was detected in EHM and R40 ( a classical laboratory mutant analysed by R.Fontana), but not in EHR, by Western blot with polyclonal anti PBP5 antibody; however, EHR produced normal amounts of this protein. Production of the other multifunctional HMM low affinity PBP reported to date (PBP3r) was also discarded by Western blot with polyclonal anti PBP3r antibodies. PBPs profiles were performed on purified membranes with 125 I-Penicillin X. A higher amount of PBP4 * ( a proteolytic product of PBP4 ) was detected in EHR as compared to the susceptible isolate. Paradoxically, competitive assays showed that PBP4 presents more affinity for Imipenem, Cefoperazone and Piperacillin in EHR. Although not yet unequivocal, this results may suggest an hypothetical role for a proteolytic cleavage associated to ß-lactam resistance development in E. hirae.