Ability of Klebsiella spp. mastitis isolates to produce virulence factors for enhanced evasion of bovine innate immune defenses

Klebsiella spp. are coliform bacteria that cause mastitis in dairy cattle and account for high mortality rates in infected cows leading to a significant financial loss. Recent outbreaks indicate that within farms a single strain can be responsible for clinical signs in multiple animals. Identification of the virulence of factors enabling Klebsiella spp. survival in the mammary glands of multiple animals may provide insight into host adaptation. In this study, Klebsiella spp. strains were evaluated for their ability to evade neutrophil killing, the primary immune defense in the bovine mammary gland. Our research focused on capsule and biofilm production by Klebsiella spp. when strains were grown in Luria Broth or skim milk to examine the effects on evasion of neutrophil killing. Biofilm production was not significantly related to the ability to resist neutrophil killing nor was capsule (P = 0.29). Farm (P < 0.001), media type (P < 0.005), and strain type by cow (P < 0.001) were found to play significant roles in neutrophil evasion. This suggests farm of origin, media type used, and cow all may play a role in evasion of neutrophils by Klebsiella spp. Further evaluation of virulence factor expression in different media types and the role of individual cow immune responses may provide insight into ability of Klebsiella spp. to cause outbreaks of mastitis in multiple animals.