Enhanced efficacy of putative efflux pump inhibitor/antibiotic combination treatments versus MDR strains of Pseudomonas aeruginosa in a Galleria mellonella in vivo infection model.
OBJECTIVE
The objectives of this study were to compare the antibiotic susceptibility of Pseudomonas aeruginosa strains with increased efflux pump expression in vitro and in vivo and to use these same strains to evaluate the efficacy of combinations of antibiotics with putative efflux pump inhibitors in vivo.


METHODS
A collection of P. aeruginosa strains that overexpress three efflux pumps (MexAB-OprM, MexCD-OprJ and MexEF-OprN), in addition to a strain with all three Mex pumps deleted, were used. The virulence of these strains and their antibiotic susceptibility was measured in vivo using a Galleria mellonella larval infection model. The inhibitory effect of combinations of putative efflux pump inhibitors (trimethoprim and sertraline) with antibiotics on the strain overexpressing MexAB-OprM was also measured in vitro and compared with their efficacy in vivo in terms of larval survival and bacterial burden.


RESULTS
Increased expression of the individual efflux pumps, or deletion of all three, had no significant effect on the virulence of P. aeruginosa in vivo. Expression levels of the efflux pumps clearly influenced antibiotic efficacy in vivo. The efficacy of levofloxacin, piperacillin and meropenem against larvae infected with the efflux pump mutants reflected susceptibility to the same drugs in vitro. Treatment of G. mellonella larvae infected with a strain that overexpressed MexAB-OprM with a combination of putative efflux pump inhibitors and levofloxacin resulted in enhanced therapeutic benefit compared with the constituent monotherapies.


CONCLUSIONS
This study has demonstrated the utility of using G. mellonella to screen for novel therapeutic options for MDR P. aeruginosa and has shown that antibiotic/efflux pump inhibitor combinations should be further investigated for clinical application.
Biomedical Sciences Research Complex, School of Biology, University of St Andrews, The North Haugh, St Andrews, Fife KY16 9ST, UK.
Dougal H
DH
Adamson
Biomedical Sciences Research Complex, School of Biology, University of St Andrews, The North Haugh, St Andrews, Fife KY16 9ST, UK.
Vasare
V
Krikstopaityte
Biomedical Sciences Research Complex, School of Biology, University of St Andrews, The North Haugh, St Andrews, Fife KY16 9ST, UK pjc5@st-andrews.ac.uk.
Peter J
PJ
Coote
D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage* / Q000494:pharmacology; D058491:Bacterial Load; D001693:Biological Transport, Active / Q000187:drug effects*; D004353:Drug Evaluation, Preclinical / Q000379:methods; D004347:Drug Interactions; D024901:Drug Resistance, Multiple, Bacterial; D017353:Gene Deletion; D007814:Larva / Q000382:microbiology / Q000502:physiology; D007915:Lepidoptera / Q000382:microbiology* / Q000502:physiology; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D008826:Microbial Sensitivity Tests; D023421:Models, Animal; D011552:Pseudomonas Infections / Q000188:drug therapy* / Q000382:microbiology; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000235:genetics; D016019:Survival Analysis
D000900:Anti-Bacterial Agents; D026901:Membrane Transport Proteins
MexAB-OprM; levofloxacin; sertraline; synergy; trimethoprim