Characterization of a novel lytic phage against multidrug-resistant Acinetobacter baumannii clinical isolates

Antibiotic-resistant Acinetobacter baumannii (A. baumannii) strains are increasing globally. It has the ability to persist under different environmental conditions. Bacteriophages are suggested as a potential alternative therapeutic approach to conventional antimicrobials. In the current study, the ΦKAB bacteriophage with its host A. baumannii was isolated from the Tigris River, Tikrit, Iraq. For molecular identification, the A. baumannii isolates were characterized by 16S rRNA and blaOXA-51-like genes. The plaque morphology of the ΦKAB phage was assessed after a long incubation period. For the phage, electron microscopy examination (TEM) revealed that phage ΦKAB is a member of the Siphoviridae family in the order Caudovirales. Evaluation of the ΦKAB phage host range showed that the ΦKAB phage was able to infect and lys12 out of 60 A. baumannii strains, including the host strain. The phage exhibited notable stability, remaining active across pH values from 4 to 11 and temperatures tolerated from -20°C to 50°C. A single-step growth experiment demonstrated a 10-minute latent period and a burst yield of 104 virions per infected cell when the multiplicity of infection (MOI) was 10. Protein profiling by SDS-PAGE revealed six detectable protein bands consisting of three major and three minor bands with molecular masses ranging from 28 to 62 kDa. Among the total A. baumannii strains, 43 (72%) A. baumannii isolates were classified as multidrug-resistant (MDR), while only 14 (23%) demonstrated resistance to carbapenem. Biofilm assessment showed that 43% of strains formed a moderate biofilm, whereas 57% exhibited weak biofilm production. Importantly, the synergistic effect of colistin-ΦKAB phage inhibited biofilm development and reduced established biofilm-associated burden. Overall, these findings demonstrated that ΦKAB possesses lytic activity, high stability at various pH and temperatures, and anti-biofilm potential, supporting its further investigation as a potential alternative approach tool for controlling infections of MDR A. baumannii. Nevertheless, additional genome sequence analysis and in vivo studies are required to determine its safety and therapeutic potential.