IMIPENEM RESISTANCE IN CLINICAL ISOLATES OF PROTEUS-MIRABILIS ASSOCIATED WITH ALTERATIONS IN PENICILLIN-BINDING PROTEINS

Two strains of Proteus mirabilis, IpR1 and IpR2, resistant to both imi penem and mecillinam, but susceptible to other beta-lactams were isola ted from blood cultures of patients who had been treated with imipenem . Strain IpR1 was isolated in the same sample as a P. mirabilis IpS1 w hich was susceptible to imipenem and mecillinam. Strains IpR1 and IpR2 did not produce a beta-lactamase and their outer membrane protein pro files were similar to those of IpS1 and P. mirabilis ATCC 29906. Elect rophoretic profiles of penicillin-binding proteins (PBPs) showed a dec rease in PBP 1A of strains IpR1 and IpR2 compared with IpS1 and ATCC 2 9906. Competition experiments revealed a decrease in affinity of PBP 2 for imipenem from strain IpR1. These findings suggest that imipenem r esistance in P. mirabilis might result from altered PBPs, as reported for Acinetobacter baumanii and Pseudomonas aeruginosa.