title: Pseudomonas aeruginosa reveals high intrinsic resistance to penem antibiotics: penem resistance mechanisms and their interplay.
abstract: Pseudomonas aeruginosa exhibits high intrinsic resistance to penem antibiotics such as faropenem, ritipenem, AMA3176, sulopenem, Sch29482, and Sch34343. To investigate the mechanisms contributing to penem resistance, we used the laboratory strain PAO1 to construct a series of isogenic mutants with an impaired multidrug efflux system MexAB-OprM and/or impaired chromosomal AmpC beta-lactamase. The outer membrane barrier of PAO1 was partially eliminated by inducing the expression of the plasmid-encoded Escherichia coli major porin OmpF. Susceptibility tests using the mutants and the OmpF expression plasmid showed that MexAB-OprM and the outer membrane barrier, but not AmpC beta-lactamase, are the main mechanisms involved in the high intrinsic penem resistance of PAO1. However, reducing the high intrinsic penem resistance of PAO1 to the same level as that of penem-susceptible gram-negative bacteria such as E. coli required the loss of either both MexAB-OprM and AmpC beta-lactamase or both MexAB-OprM and the outer membrane barrier. Competition experiments for penicillin-binding proteins (PBPs) revealed that the affinity of PBP 1b and PBP 2 for faropenem were about 1.8- and 1.5-fold lower, than the respective affinity for imipenem. Loss of the outer membrane barrier, MexAB, and AmpC beta-lactamase increased the susceptibility of PAO1 to almost all penems tested compared to the susceptibility of the AmpC-deficient PAO1 mutants to imipenem. Thus, it is suggested that the high intrinsic penem resistance of P. aeruginosa is generated from the interplay among the outer membrane barrier, the active efflux system, and AmpC beta-lactamase but not from the lower affinity of PBPs for penems.
authors.affiliation: Department of Microbiology, Kyoto Pharmaceutical University, Yamashina, Kyoto 607-8414, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Okamoto
authors.forename: N
authors.initials: N
authors.lastname: Gotoh
authors.forename: T
authors.initials: T
authors.lastname: Nishino
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001425:Bacterial Outer Membrane Proteins / Q000096:biosynthesis / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D015780:Carbapenems / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D006801:Humans; D007769:Lactams; D026901:Membrane Transport Proteins; D008826:Microbial Sensitivity Tests; D018272:Porins / Q000096:biosynthesis; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D018440:beta-Lactam Resistance / Q000235:genetics / Q000502:physiology*; D001618:beta-Lactamases / Q000172:deficiency / Q000378:metabolism; D047090:beta-Lactams
chemical_list: D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D015780:Carbapenems; D002352:Carrier Proteins; D007769:Lactams; D026901:Membrane Transport Proteins; C118598:MexA protein, Pseudomonas aeruginosa; C118597:MexB protein, Pseudomonas aeruginosa; C109237:OmpF protein; C402263:OprM protein, Pseudomonas aeruginosa; D018272:Porins; D047090:beta-Lactams; C040033:ritipenem; C048795:AmpC beta-lactamases; D001618:beta-Lactamases; C107057:fropenem