Reduced production of OprM may promote oprD mutations and lead to imipenem resistance in Pseudomonas aeruginosa carrying an oprD-group 1A allele.
Resistance mechanisms in a group of carbapenemase-negative Pseudomonas aeruginosa that were susceptible to all antibiotics except carbapenems (carbapenem resistance-only P. aeruginosa [CROPA]) were studied. Ten genetically nonrelated CROPA isolates and their carbapenem-susceptible counterparts were further investigated. OprD production was demonstrated by protein electrophoresis in only 1 of the 10 carbapenem-susceptible isolates, while the other 9 isolates showed hyperproduction of OprM. DNA sequencing of oprD revealed a shortened loop 7 domain (group 1A allele) in eight carbapenem-susceptible isolates. Various oprD mutations, leading to early terminations, were found in 9 of the 10 CROPA isolates. RNA analysis demonstrated hyperexpression of oprM with normal expression of mexA in eight of the carbapenem-susceptible isolates, while in seven of their CROPA counterparts, the oprM expression was significantly reduced. Deletion of oprM was performed in two pairs of representative isolates. Selection of imipenem resistant variants by a disc assay indicated that the lost-of-function mutations in oprD occurred relatively faster in the ΔoprM mutants compared with their corresponding parent strains. Under selection pressure, reduced production of OprM may promote the selection of spontaneous changes in oprD, resulting in the carbapenem resistance in a group of pan-susceptible P. aeruginosa isolates characterized by harboring an oprD-group 1A allele.
1 Department of Medical Biotechnology and Laboratory Science, College of Medicine, Chang Gung University , Taoyuan, Taiwan .
Jwu-Ching
JC
Shu
Lin-Hui
LH
Su
Cheng-Hsun
CH
Chiu
An-Jing
AJ
Kuo
Tsui-Ping
TP
Liu
Ming-Hsun
MH
Lee
I-Ning
IN
Su
Tsu-Lan
TL
Wu
D000483:Alleles; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics; D015780:Carbapenems / Q000494:pharmacology; D004269:DNA, Bacterial / Q000235:genetics; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D015378:Imipenem / Q000494:pharmacology*; D026901:Membrane Transport Proteins / Q000235:genetics*; D009154:Mutation / Q000235:genetics*; D018272:Porins / Q000235:genetics*; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000235:genetics*; D001618:beta-Lactamases / Q000235:genetics
D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D015780:Carbapenems; D004269:DNA, Bacterial; D026901:Membrane Transport Proteins; C402263:OprM protein, Pseudomonas aeruginosa; D018272:Porins; C077157:OprD protein, Pseudomonas aeruginosa; D015378:Imipenem; D001618:beta-Lactamases; C063912:carbapenemase