A Galleria mellonella infection model reveals double and triple antibiotic combination therapies with enhanced efficacy versus a multi-drug resistant strain of Pseudomonas aeruginosa.

The aim of this study was to compare the inhibitory effect of antibiotic combinations in vitro with efficacy in G. mellonella larvae in vivo to identify efficacious combinations that target P. aeruginosa. P. aeruginosa NCTC13437, a MDR strain resistant to -lactams and aminoglycosides, was used. Susceptibility to CTX, PIP, MER, AMK, LVX and CST alone, or in dual or triple combinations, was measured in vitro via a 24 h time-kill assay. In vitro results were then compared with the efficacy of the same dual or triple antibiotic combinations versus G. mellonella larvae infected with P. aeruginosa. G. mellonella haemolymph burden of P. aeruginosa was determined over 96 h post-infection and treatment with the most potent combination therapies. Many dual and triple combinations of antibiotics displayed synergistic inhibition of MDR P. aeruginosa in vitro. There was little correlation between combinations that were synergistic in vitro and those that showed enhanced efficacy in vivo versus infected G. mellonella larvae. The most potent dual and triple combinations in vivo were CTX + PIP and MER + PIP + AMK respectively. Fewer combinations were found to offer enhanced therapeutic benefit in vivo compared to in vitro. The therapeutic benefit arising from treatment with antibiotic combinations in vivo correlated with reduced larval burden of P. aeruginosa. This study has identified antibiotic combinations that merit further investigation for their clinical potential and has demonstrated the utility of using G. mellonella to screen for novel antibiotic treatments that demonstrate efficacy in vivo.