In vitro Evaluation of Lytic Phages for Carbapenem-Resistant Klebsiella pneumoniae Isolates

Klebsiella pneumoniae is a dominate cause of sever community-acquired and nosocomial infections, specifically among immunocompromised individuals. The increasing occurrence of multidrug-resistant (MDR) isolates has significantly impacted the effectiveness of antimicrobial agents. As we have entered the post antibiotic era, the use of bacteriophages to treat pathogenic bacterial infections is becoming revitalized. Elucidating molecular details of phage-bacteria interactions will provide insights into phage biology and better development of phage therapies. In this study, a total of 22 non-duplicate K. pneumoniae isolates were assessed for their genetic and phenotypic relatedness by multi-locus sequence typing (MLST), endonuclease S1 nuclease pulsed-field gel electrophoresis (S1-PFGE) and in vitro antibiotic susceptibility testing. Further, the beta-lactamase gene (blaKPC) was characterized to determine the spread and outbreak of K. pneumoniae carbapenemase (KPC)-producing enterobacterial pathogens. Three phages were isolated and characterized to evaluate the application of lytic phages against these 22 ST11 K. pneumoniae isolates. In vitro inhibition assays demonstrated the lytic potential of three relatively broad host-range phages, imposing strong selections for phage-resistant mutants. Comparative genomic sequence analyses revealed that phage-resistant mutants harbored mutations in gene wcaJ, which is essential for the biosynthesis of colanic acid. Together, this data suggests that in vitro characterization of phage-host interactions adds more comprehensive knowledge to known anti-phage defense strategies and further emphasizes their complexity and future challenges to overcome prior to using phages for controlling this important MDR bacterium.