Abstract
Antibiotics are losing efficacy due to the rapid evolution and spread of resistance. Treatments targeting bacterial virulence factors have been considered as alternatives because they target virulence instead of pathogen viability, and should therefore exert weaker selection for resistance than conventional antibiotics. However, antivirulence treatments rarely clear infections, which compromises their clinical applications. Here, we explore the potential of combining antivirulence drugs with antibiotics against the opportunistic human pathogen Pseudomonas aeruginosa. We combined two antivirulence compounds (gallium, a siderophore-quencher, and furanone C-30, a quorum sensing-inhibitor) together with four clinically relevant antibiotics (ciprofloxacin, colistin, meropenem, tobramycin) in 9×9 drug concentration matrices. We found that drug-interaction patterns were concentration dependent, with promising levels of synergies occurring at intermediate drug concentrations for certain drug pairs. We then tested whether antivirulence compounds are potent adjuvants, especially when treating antibiotic resistant clones. We found that the addition of antivirulence compounds to antibiotics could restore growth inhibition for most antibiotic resistant clones, and even abrogate or reverse selection for resistance in five drug combination cases. Molecular analyses suggest that selection against resistant clones occurs when resistance mechanisms involve restoration of protein synthesis, but not when efflux pumps are upregulated. Altogether, our work provides a first systematic analysis of antivirulence-antibiotic combinatorial treatments and suggests that such combinations have a high potential to be both effective in treating infections and in limiting the spread of antibiotic resistance.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
This revised version contains new data on (i) cross resistance and collateral sensitivity of antibiotic resistant clones to the antivirulence compounds (Figure 5, Supplementary Figure S5), and (ii) the effect of antivirulence compounds on the selection for or against antibiotic resistant clones (Figure 6).
