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

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.

Antibody and skin-test responses of sheep vaccinated against Johne's Disease.

Current vaccines against Mycobacterium avium subsp. paratuberculosis (MAP, Johne's Disease) may cause animals to react positively when tested for Mycobacterium bovis (Bovis). Therefore, the effects of vaccination on MAP serum Ab and skin-test responses to MAP and Bovis PPD were compared in 25 ewes vaccinated against MAP with 24 control ewes in an infected flock 3 years post-vaccination. MAP-specific Ab levels were higher (P<0.001) in vaccinated ewes than in control ewes. All increases in skinfold-thickness from 0 to 48h were greater (P<0.0001) than zero while increases in skinfold-thickness from 48 to 72h were greater (P<0.05) than zero for Johnin but not for Bovis PPD. The Vaccine x PPD x Time interaction for skinfold-thickness was significant (P<0.001) with greater increases to Johnin than to Bovis, but with much greater increases in vaccinated ewes. These data suggest that administration of vaccines against MAP developed from whole organisms increase the likelihood that animals will be classified as "responders" to a Bovis screening test and negative by the follow-up comparative cervical tuberculin test, but they also show that vaccination initiates both humoral and cell-mediated MAP-specific responses.