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. 2024;100(1):57-67.
doi: 10.2183/pjab.100.006.

Changes in the expression of mexB, mexY, and oprD in clinical Pseudomonas aeruginosa isolates

Yoshimi Matsumoto  1 , Seiji Yamasaki  1   2   3 , Kouhei Hayama  1 , Ryota Iino  4   5 , Hiroyuki Noji  6 , Akihito Yamaguchi  1 , Kunihiko Nishino  1   2   7
Affiliations

Changes in the expression of mexB, mexY, and oprD in clinical Pseudomonas aeruginosa isolates

Yoshimi Matsumoto et al. Proc Jpn Acad Ser B Phys Biol Sci. 2024.

Abstract

Changes in expression levels of drug efflux pump genes, mexB and mexY, and porin gene oprD in Pseudomonas aeruginosa were investigated in this study. Fifty-five multidrug-resistant P. aeruginosa (MDRP) strains were compared with 26 drug-sensitive strains and 21 strains resistant to a single antibiotic. The effect of the efflux inhibitor Phe-Arg-β-naphthylamide on drug susceptibility was determined, and gene expression was quantified using real-time quantitative real-time reverse transcription polymerase chain reaction. In addition, the levels of metallo-β-lactamase (MBL) and 6'-N-aminoglycoside acetyltransferase [AAC(6')-Iae] were investigated. Efflux pump inhibitor treatment increased the sensitivity to ciprofloxacin, aztreonam, and imipenem in 71%, 73%, and 29% of MDRPs, respectively. MBL and AAC(6')-Iae were detected in 38 (69%) and 34 (62%) MDRP strains, respectively. Meanwhile, 76% of MDRP strains exhibited more than 8-fold higher mexY expression than the reference strain PAO1. Furthermore, 69% of MDRP strains expressed oprD at levels less than 0.01-fold of those in PAO1. These findings indicated that efflux pump inhibitors in combination with ciprofloxacin or aztreonam might aid in treating MDRP infections.

Keywords: Phe-Arg-β-naphthylamide; aminoglycoside acetyltransferase; metallo-β-lactamase; multidrug efflux pumps; multidrug resistance.

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Figures

Figure 1.
Figure 1.
Cumulative MICs for each antimicrobial agent in the presence or absence of the inhibitors. AMK, CIP, IPM, and ATM + PAN: combination treatment with PAN; +DPA: combination treatment with DPA. a)-1–a)-4 SP: 26 drug-sensitive strains; b)-1–b)-4 RP: 21 drug-resistant strains excluding MDR, and c)-1–c)-4 MDRP: 55 MDR strains. The horizontal axis shows the MIC concentration of each antibacterial agent (mg/L), and the vertical axis shows the cumulative percentage of isolates whose growth was inhibited at the corresponding MIC concentration of each antibacterial agent. MIC, minimum inhibitory concentration; AMK, amikacin; CIP, ciprofloxacin; IPM, imipenem; ATM, aztreonam; PAN, Phe-Arg-β-naphthylamide; DPA, dipicolinic acid; SP, drug-sensitive Pseudomonas aeruginosa; RP, drug-resistant Pseudomonas aeruginosa; MDRP, multidrug-resistant Pseudomonas aeruginosa.
Figure 2.
Figure 2.
MBL production and effect of PAN on the cumulative MICs for IPM and ATM. The horizontal axis shows the MIC concentration of each antibacterial agent (mg/L), and the vertical axis shows the cumulative percentage of isolates whose growth was inhibited at the corresponding MIC concentration of each antibacterial agent. MBL, metallo-β-lactamase; PAN, Phe-Arg-β-naphthylamide; MIC, minimum inhibitory concentration; IPM, imipenem; ATM, aztreonam.
Figure 3.
Figure 3.
Combinatorial patterns of resistance factors among the resistance groups. By defining the effective expression changes as greater than 4-fold for mexB, greater than 8-fold for mexY, and less than 0.01-fold for oprD, frequencies of zero, one, two, or three changes in the expression of the genes are presented for each group. SP: 26 drug-sensitive strains; RP: 21 drug-resistant strains excluding MDR; MDRP (−)MBL: 17 MDR strains that did not produce MBL; MDRP (+)MBL: 38 MDR strains producing MBL. MDR, multidrug resistance; MDRP, multidrug-resistant Pseudomonas aeruginosa; MBL, metallo-β-lactamase.
Figure 4.
Figure 4.
Correlation between the levels of mexB and the MICs for CIP or ATM. Gene levels are presented as ratios of the test strain value to that of the reference strain PAO1. MIC, minimum inhibitory concentration; CIP, ciprofloxacin; ATM, aztreonam.
Figure 5.
Figure 5.
Correlation between the levels of mexY and the MICs for AMK or CIP. Gene levels are presented as ratios of the test strain value to that of the reference strain PAO1. MIC, minimum inhibitory concentration; AMK, amikacin; CIP, ciprofloxacin.
Figure 6.
Figure 6.
Correlation between the levels of oprD and MICs for IPM. Gene levels are presented as ratios of the test strain value to that of the reference strain PAO1. The dashed rectangle denotes decreased expression of oprD in sensitive strains. MIC, minimum inhibitory concentration; IPM, imipenem.
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