title: Moraxella catarrhalis AcrAB-OprM efflux pump contributes to antimicrobial resistance and is enhanced during cold shock response.
abstract: Moraxella catarrhalis is a common pathogen of the human respiratory tract. Multidrug efflux pumps play a major role in antibiotic resistance and virulence in many Gram-negative organisms. In the present study, the role of the AcrAB-OprM efflux pump in antibiotic resistance was investigated by constructing mutants that lack the acrA, acrB, and oprM genes in M. catarrhalis strain O35E. We observed a moderate (1.5-fold) decrease in the MICs of amoxicillin and cefotaxime and a marked (4.7-fold) decrease in the MICs of clarithromycin for acrA, acrB, and oprM mutants in comparison with the wild-type O35E strain. Exposure of the M. catarrhalis strains O35E and 300 to amoxicillin triggered an increased transcription of all AcrAB-OprM pump genes, and exposure of strains O35E, 300, and 415 to clarithromycin enhanced the expression of acrA and oprM mRNA. Inactivation of the AcrAB-OprM efflux pump genes demonstrated a decreased ability to invade epithelial cells compared to the parental strain, suggesting that acrA, acrB, and oprM are required for efficient invasion of human pharyngeal epithelial cells. Cold shock increases the expression of AcrAB-OprM efflux pump genes in all three M. catarrhalis strains tested. Increased expression of AcrAB-OprM pump genes after cold shock leads to a lower accumulation of Hoechst 33342 (H33342), a substrate of AcrAB-OprM efflux pumps, indicating that cold shock results in increased efflux activity. In conclusion, the AcrAB-OprM efflux pump appears to play a role in the antibiotic resistance and virulence of M. catarrhalis and is involved in the cold shock response.
authors.affiliation: Institute for Infectious Diseases, University of Bern, Bern, Switzerland violeta.spaniol@ifik.unibe.ch.
authors.forename: Violeta
authors.initials: V
authors.lastname: Spaniol
authors.affiliation: Institute for Infectious Diseases, University of Bern, Bern, Switzerland.
authors.forename: Sara
authors.initials: S
authors.lastname: Bernhard
authors.affiliation: Institute for Infectious Diseases, University of Bern, Bern, Switzerland Department of Pediatrics, University of Bern, Inselspital, Bern, Switzerland.
authors.forename: Christoph
authors.initials: C
authors.lastname: Aebi
mesh_terms: D000658:Amoxicillin / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D002439:Cefotaxime / Q000494:pharmacology; D002460:Cell Line; D017291:Clarithromycin / Q000494:pharmacology; D058639:Cold-Shock Response; D004269:DNA, Bacterial / Q000235:genetics; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D004847:Epithelial Cells / Q000382:microbiology; D006801:Humans; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism*; D008826:Microbial Sensitivity Tests; D001936:Moraxella catarrhalis / Q000235:genetics* / Q000378:metabolism*; D009154:Mutation / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D026901:Membrane Transport Proteins; D000658:Amoxicillin; D017291:Clarithromycin; D002439:Cefotaxime