Short communication: Comparison of virulence factors in Klebsiella pneumoniae strains associated with multiple or single cases of mastitis

Abstract

Klebsiella pneumoniae mastitis in dairy cattle is generally due to an opportunistic infection from the environment, resulting in large heterogeneity among mastitis-causing strains within a herd. However, in mastitis outbreaks in 4 herds, several strains of K. pneumoniae were identified as the cause of infection in multiple cows, suggesting increased ability to either cause disease or evade host defenses. In this study, differences in capsule formation and immune evasion were compared in 5 pairs of K. pneumoniae strains, where one strain in each pair was associated with multiple cases of mastitis and the other with a single case of mastitis. Production of capsular polysaccharide, ability to evade killing by polymorphonuclear neutrophilic leukocytes (PMNL), and the relationship between the 2 were evaluated for each strain grown in broth or milk. Growth of isolates in skim milk increased capsule size and ability to evade killing by PMNL, depending on strain type. Specifically, strains associated with multiple cases of mastitis had increased capsule size in skim milk. Strains associated with single cases of mastitis were better able to evade killing by PMNL when grown in skim milk. Our results, although preliminary, suggest that the 2 groups of strains may constitute different subpopulations of K. pneumoniae. However, our findings do not indicate that capsule or evasions of killing by PMNL explain increased mastitis outbreaks with Klebsiella. Further work will explain the enhanced ability of some strains to cause mastitis in dairy cows.

Extensive capsule locus variation and large-scale genomic recombination within theKlebsiella pneumoniaeclonal complex 258/11

“…The K. pneumoniae ST442/ wzi- 154 strain in this study was isolated from a case of bovine mastitis at a dairy farm in New York State in 2006 (36), which is geographically close to the location of the first reports of ST258 in New York in 2000 (37). The ST42/ wzi- 29 was isolated in 1996 from a blood stream infection in a hospital in Singapore (38).…”

Evaluation of a commercial real-time multiplex PCR assay for the detection of bovine mastitis pathogens directly from milk

“…Two of these studies found significant numbers of samples that were culture negative/PCR positive for Staphylococcus spp. and C. bovis Zadoks et al, 2014).…”

“…Clinical milk samples have been used to compare conventional culture methods to PathoProof PCR in previous studies (Cederlöf et al, 2012;Zadoks et al, 2014). With the exception of Hiitiö et al,…”

“…Klebsiella pneumoniae has become significant in human medicine in the ongoing battle with multidrug resistant bacteria in hospital environments (Diancourt et al, 2005). Klebsiella pneumoniae resists attack by PMNs due to a thick polysaccharide capsule production that surrounds the outer membrane of the bacterium (Kanevsky-Mullarky et al, 2014). This capsule also makes K. pneumoniae distinguishable on an agar plate due to the mucoid appearance of the colonies .…”

“…Real-time PCR is a sensitive and specific assay previously evaluated to detect mastitis pathogens and aid the diagnosis of mastitis with success although commercial assays were unavailable. PathoProof PCR has been validated in several studies that evaluate the assay's sensitivity and specificity with culture isolates Pitkälä et al, 2007) and clinical milk samples (Cederlöf et al, 2012;Zadoks et al, 2014). Nearly one third of clinical milk samples are culture negative for a variety of reasons, not all of them known.…”