Vaccination against experimental staphylococcosis in sheep -- observations on bacteriology and pathology following challenge.

Sheep were vaccinated with a killed Staphylococcus aureus vaccine (2 doses) which had been cultured in vitro (Group 1), a killed S. aureus vaccine (2 doses) cultured in vivo (Group 2) or a single dose of a live vaccine (Group 3). Other sheep were used as non-vaccinated controls. All sheep were challenged by intravenous injection of 2.6 x 10(11) washed, viable S. aureus organisms, the vaccinated animals being given the challenge inoculum at various intervals after vaccination. The control sheep survived for 29h (mean) after challenge. Animals given killed vaccines survived longer, (particularly Group 2) if challenged less than 40 days post-vaccination, compared with those challenged more than 40 days post-vaccination. Animals in Group 3 survived longer if challenged after 40 days post-vaccination than those in Groups 1 or 2. There were no significant differences between the treatment groups for numbers of S. aureus recovered from blood in the 3h period following challenge. Histological and bacteriological evidence showed that the kidneys were more severely affected by the challenge inoculum than heart, spleen, liver or lungs. The kidneys showed both toxigenic and lymphoreticular reactions and large numbers of staphylococci were recovered more reliably from kidneys than other organs.