Functional analysis and anti-virulent properties of a new depolymerase from a myovirus that infects Acinetobacter baumannii capsule K45.

Abstract

Acinetobacter baumannii is an important pathogen causative of health care-associated infections and is able to rapidly develop resistance to all known antibiotics, including colistin. As an alternative therapeutic agent, we have isolated a novel myovirus (vB_AbaM_B9) which specifically infects and makes lysis from without in strains of the K45 and K30 capsule types, respectively. Phage B9 has a genome of 93,641 bp and encodes 167 predicted proteins, of which 29 were identified by mass spectrometry. This phage holds a capsule depolymerase (B9gp69) able to digest extracted exopolysaccharides of both K30 and K45 strains and remains active in a wide range of pH values (5 to 9), ionic strengths (0 to 500 mM), and temperatures (20 to 80°C). B9gp69 was demonstrated to be nontoxic in a cell line model of the human lung and to make the K45 strain fully susceptible to serum killing in vitro. Contrary to the case with phage, no resistance development was observed by bacteria targeted with the B9gp69. Therefore, capsular depolymerases may represent attractive antimicrobial agents against A. baumannii infections.