Characterization of lytic bacteriophages of Klebsiella pneumoniae with capsular depolymerases

Abstract

Klebsiella pneumoniae is a Gram-negative opportunistic pathogen responsible for a wide range of nosocomial and community-acquired infections. The bacterium is increasingly difficult to treat and K. pneumoniae is considered a reservoir of antimicrobial resistance genes, including those encoding resistance to carbapenems and colistin. K. pneumoniae forms biofilms that further inhibit the uptake and efficacy of current antibiotics. Treatment difficulties are compounded by phenotypic diversity among K. pneumoniae isolates, with the bacterium having 78 recognized capsular (K) types. Alternative treatment options for K. pneumoniae infections are vital, and interest in the potential of bacteriophage therapies that target this bacterium is increasing. A hypervirulent intestinal isolate of K. pneumoniae, L4-FAA5 (K2:O1, ST380), has been used as a host strain to isolate lytic bacteriophages from mixed-liquor sewage samples. Three bacteriophages have been identified as having unique DNA restriction enzyme profiles, and their DNA has been submitted for whole-genome sequencing. Each bacteriophage appears to encode a depolymerase, as evidenced by formation of haloes around plaques in double-agar overlays seeded with L4-FAA5. When tested against 13 clinical isolates of K. pneumoniae (including K2 and unknown K, NDM, OXA-48 and KPC types), none of the bacteriophages (along with KLPN1) lysed any of the isolates; however, suspected depolymerase activity was observed for 10 of the 13 isolates tested. To this end, the project seeks to confirm the presence of depolymerases in the genomes of the three new bacteriophages, and to assess their efficacy as biofilm-degrading enzymes useful as adjuncts to antibiotic or lysin therapy.