Isolation and Characterisation of Bacteriophage Selective for Key Acinetobacter baumannii Capsule Chemotypes

Nineteen bacteriophages against five main capsular types of multidrug-resistant Acine-tobacter baumannii were isolated from tertiary care hospital sewage. Eight representative phages from each capsular type were characterized and tested for their biological properties. The biological features revealed that phages T1245, T444, and T515 had a large burst size of more than 420 pfu/mL, together with a short latent period lasting less than 6 min, and were readily adsorbed to a bacterial host within 10 min. Moreover, these phages demonstrated host specificity and stability over a broad range of temperatures (−20 to 60^◦C) and pH (5.0–9.0). A whole-genome analysis of six lytic and two temperate phages revealed high genomic similarity with double-stranded DNA between 40 and 50 kb and G + C content of 38–39%. The protein compositions disclosed the absence of toxin-coding genes. The phylogenic results, together with morphological micrographs, confirmed that three selected phages (T1245, T444, and T515) belong to the Podoviridae family within the order Caudovirales. The biological data and bioinformatics analysis indicated that these novel A. baumannii phages possess important enzymes, including depolymerase and endolysin, which could be further developed as promising alternative antibacterial agents to control A. baumannii infections.