Participation of PBP 3 in the acquisition of dicloxacillin resistance in Listeria monocytogenes.

Purified membranes of Listeria monocytogenes ATCC 15313 contain at least five penicillin-binding proteins. In two dicloxacillin-resistant mutants, derived from a sensitive parent strain, a 16-fold increase in the MIC of dicloxacillin was observed. A less-significant increase was detected in the MICs of other beta-lactam drugs. In the mutants, PBP 3 lost its strong affinity for dicloxacillin, but remained fully susceptible to binding of 125I-penicillin X, as compared with the wild-type strain. PBP 2 could not be detected in one of the mutants. No decrease in affinity for the radioactive tracer or dicloxacillin was detected in any other PBP of the resistant mutants.