Synergy of a virulent phage (φAB182) with antibiotics leading to successful elimination of biofilms formed by MDR Acinetobacter baumannii .

Emergence of multiple drug resistant (MDR) strains of Acinetobacter baumannii and a withering drug discovery pipeline necessitates the search for effective alternatives to replace or synergize with currently used antibiotics. In this report, we have described the synergy assessment of a virulent Acinetobacter baumannii phage φAB182 with a wide range of antibiotics. Myophage φAB182 was isolated from sewage against MDR A. baumannii and exhibited maximum stability at 25 °C and pH 7. It also had a short latent period of 9 min with a large burst size of 287. The phylogenetic analysis of its major capsid protein gene indicated an 84.15% similarity to the lytic  A. baumannii phage Acj9. In the presence of antibiotics, phage φAB182 showed the highest synergy ( p  < 0.0001) with colistin, followed by polymixin B, ceftazidime and cefotaxime and this synergistic effect was further validated by time kill kinetics. The combined action of phage φAB182 with colistin, polymixin B, ceftazidime and cefotaxime was also synergistic for the eradication of biofilms formed by A. baumannii as measured by MBECcombination /MBECantibiotic values (<0.25). We thus propose bacteriophage φAB182 as a potential antibacterial candidate in combination therapy. The findings from this study strongly support the use of phage antibiotic synergy for the successful treatment of biofilm forming MDR A. baumannii infections.