Investigating the phenotypic alterations associated with hypermucoviscous hypervirulent Klebsiella pneumoniae during phage resistance development.

Phage therapy has been explored and used compassionately in the post-antibiotic era, though phage resistance might pose a serious challenge. The advent of hypervirulent and hypermucoviscous traits in Klebsiella pneumoniae limits therapeutic choices. This study investigated the phage resistance in hypermucoviscous hypervirulent Klebsiella pneumoniae clinical strain Kleb_53. A Klebsiella phage Disc against the Kleb_53 strain was isolated from sewage. The phage exhibited stability between - 20 °C and 60 °C and within the pH range of 3 to 11. The phage adsorption time was 15 min, with a latent period of 30 min and a burst size of 354 virions. The phage-resistant Kleb_53 variants were screened and examined for their phenotypic variations, antibiotic susceptibility, and biofilm formation. Colony morphotype variants were observed, including smooth, rough, and small colony variants. String, aggregation, and wetness tests confirmed reduced mucoviscosity. The plaque morphology differed between the wild and variants. Additionally, resistance to meropenem and third-generation cephalosporins was reversed, whereas the biofilm-forming ability varied among the recovered variants. This study demonstrates that ongoing phage-host interactions drive phenotypic changes and the emergence of phage-resistant variants with altered antibiotic susceptibility and biofilm-forming capacity. It also underscores the need for further research on phage resistance and strategies to overcome it for the effective application of phage therapy.