CATECHOLIC BETA-LACTAMS - FACILITATED TRANSPORT

Non-β-lactamase-mediated insusceptibility to βlactams was studied in Haemophihis influenzae. Mutants resistant to ampicillin were selected in a susceptible isolate, while phenotypically similar resistance was transformed from four wild-type isolates into asusceptible recipient. Ampicillin-selected mutants generally had reduced susceptibility to penicillins, cephalosporins and aztreonam. Reduced susceptibility to mercpenem was less common, and susceptibility to imipenem was unaffected. MICs of three cephalosporins and aztreonam were much higher for the ampicillin-resistanttransformants than for the recipient strain, and were generallyequal to, or within one doubling dilution of, the concentrations that inhibited the donor parents. Incontrast, reduced susceptibility to imipenem observed with one parent (MIC of4 mg/1) was not transferred to the recipient(MIC of 0-5 mg/1). Meropcnem inhibited22 of 24 transformants tested at <012 mg/1, compared with MICs of > 0-5mg/1for the donor parents and 0-03 mg/1 for the recipient. These results indicated that themechanisms that confer non---lactamase-mediated insusceptibility to penicillins,cephalosporins and aztreonam in H.influenzae have little or no effect on susceptibility to carbapenems. © 1990, by The British Society for Antimicrobial Chemotherapy.