LAUSR

OBJECTIVES Klebsiella (K.) pneumoniae is an emerging invasive pathogen in humans and pigs. Resistance against multiple antibiotics in this species is a major health concern and development of new antibiotics is urgently needed. The objective of this study was to investigate effects of proline-rich antimicrobial peptides on survival of K. pneumoniae strains in porcine blood. METHODS We established a bactericidal assay with Klebsiella pneumoniae in fresh blood drawn from 4-week-old piglets. Proline-rich antimicrobial peptides, namely the apidaecins Api137 and Api802 as well as the oncocin Onc112, were added to ex vivo infected whole blood samples to study bactericidal effects and in the case of Api137 also immune responses. RESULTS A porcine invasive as well as an human iucA+rmpA+ K. pneumoniae strain showed prominent proliferation in porcine blood. Application of Api137 resulted in a dose-dependent prominent bactericidal effect killing the invasive porcine K. pneumoniae strain. Addition of 8 µg/ml Api137 resulted also in complete killing of the human iucA + rmpA+ strain. Cytotoxicity, hemolysis and induction of the proinflammatory cytokine TNF-α in K. pneumoniae infected porcine blood treated with Api137 was comparable to values obtained after application of 10 µg/ml cefquinome. CONCLUSION We describe a new non-rodent model for invasive K. pneumoniae bacteremia and present promising data for the proline-rich antimicrobial peptide Api137 for the control of infection with hypervirulent strains.