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Abstract Background Klebsiella pneumoniae capsular types K1, K2, K5, K20, K54, and K57 are prevalent hypervirulent types associated with community infections, and worrisomely, hypervirulent strains that acquired drug resistance have been found. In the search for alternative therapeutics, studies have been conducted on phages that infect K. pneumoniae K1, K2, K5, and K57-type strains and their phage-encoded depolymerases. However, phages targeting K. pneumoniae K20-type strains and capsule depolymerases capable of digesting K20-type capsules have rarely been reported. In this study, we characterized a phage that can infect K. pneumoniae K20-type strains, phage vB_KpnM‐20. Methods A phage was isolated from sewage water in Taipei, Taiwan, its genome was analyzed, and its predicted capsule depolymerases were expressed and purified. The host specificity and capsule-digesting activity of the capsule depolymerases were determined. The therapeutic effect of the depolymerase targeting K. pneumoniae K20-type strains was analyzed in a mouse infection model. Results The isolated Klebsiella phage, vB_KpnM‐20, infects K. pneumoniae K7, K20, and K27-type strains. Three capsule depolymerases, K7dep, K20dep, and K27dep, encoded by the phage were specific to K7, K20, and K27-type capsules, respectively. K20dep also recognized Escherichia coli K30-type capsule, which is highly similar to K. pneumoniae K20-type. The survival of K. pneumoniae K20-type-infected mice was increased following administration of K20dep. Conclusions The potential of capsule depolymerase K20dep for the treatment of K. pneumoniae infections was revealed using an in vivo infection model. In addition, K7dep, K20dep, and K27dep capsule depolymerases could be used for K. pneumoniae capsular typing.

Abstract Background Streptococcus pneumoniae is a common cause of post-influenza secondary bacterial infection, which results in excessive morbidity and mortality. Although 13-valent pneumococcal conjugate vaccine (PCV13) vaccination programs have decreased the incidence of pneumococcal pneumonia, PCV13 failed to prevent serotype 3 pneumococcal disease as effectively as other vaccine serotypes. We aimed to investigate the mechanisms underlying the co-pathogenesis of influenza virus and serotype 3 pneumococci. Methods We carried out a genome-wide screening of a serotype 3 S. pneumoniae transposon insertion mutant library in a mouse model of coinfection with influenza A virus (IAV) to identify the bacterial factors required for this synergism. Results Direct, high-throughput sequencing of transposon insertion sites identified 24 genes required for both coinfection and bacterial infection alone. Targeted deletion of the putative aminotransferase (PA) gene decreased bacterial growth, which was restored by supplementation with methionine. The bacterial burden in a coinfection with the PA gene deletion mutant and IAV in the lung was lower than that in a coinfection with wild-type pneumococcus and IAV, but was significantly higher than that in an infection with the PA gene deletion mutant alone. These data suggest that IAV infection alters host metabolism to benefit pneumococcal fitness and confer higher susceptibility to pneumococcal infection. We further demonstrated that bacterial growth was increased by supplementation with methionine or IAV-infected mouse lung homogenates. Conclusions The data indicates that modulation of host metabolism during IAV infection may serve as a potential therapeutic intervention against secondary bacterial infections caused by serotype 3 pneumococci during IAV outbreaks in the future.