Ovine opsonins for Staphylococcus aureus cell wall and pseudocapsule

Electron microscopic study of milk sediments. Qualitative and quantitative observations

Sediment of milk from ovine mammary glands infected experimentally with coagulase-negative staphylococci was examined by transmission electron microscopy. The proportions, of the various particles and cells present in milk and of macrophages and neutrophils involved in phagocytosis were determined 6 h, 18 h and 49 days after infection. All cell types together predominated over cytoplasmic bodies in approximately 54% of normal milk samples. The proportion of macrophages in normal milk was higher than that of neutrophils in approximately 69% of samples examined. After infection and in the early phase of inflammation, the proportion changed in favour of neutrophils. In both the early and late phases of infection, greater numbers of macrophages (3-27.2%) than neutrophils (0-2.7%) contained phagocytized cocci. Moreover, greater numbers of cocci were observed in macrophages than in neutrophils (mean values 8.1 vs 1.2), indicating the importance of the macrophage in the maintenance of ovine subclinical mastitis caused by coagulase negative staphylococci.

Further studies on the efficacy of a live vaccine against mastitis caused by Streptococcus uberis

Three groups of dairy cows were immunized by subcutaneous (s.c.) administration of a preparation of live Streptococcus uberis (strain 0140J) and an intramammary infusion of a soluble surface extract derived from same the bacteria. Animals in Groups 1 and 2 received two s.c. vaccinations plus an intramammary inoculation. Animals in Group 3 received two s.c. vaccinations but did not receive the intramammary infusion. In addition to the vaccinated animals, each group also contained two non-vaccinated (control) animals. All animals were challenged experimentally by intramammary infusion (in two quarters per animal) of ca 100 c.f.u. of S. uberis (strain 0140J or C221) and monitored for clinical signs of disease, bacterial numbers in milk, somatic cell count in milk, and daily milk yield for the following 10 days. Animals in Group I were challenged with strain 0140J. Only one out of six challenged quarters of three vaccinated cows developed clinical disease compared to all (four out of four) quarters of non-vaccinated cows. Animals in Group 2 were challenged with strain C221. All challenged quarters of three vaccinated (six out of six) and two non-vaccinated (four out of four) cows developed clinical mastitis. Animals in Group 3 were challenged with strain 0140J. Five out of eight quarters on four vaccinated cows developed clinical mastitis but the onset was delayed in comparison with that in both non-vaccinated cows in which four out of four challenged quarters developed clinical mastitis. These results indicated that vaccination with live S. uberis protects against challenge with the homologous strain but was less effective against a heterologous strain. Reduced protection was also seen when the intramammary booster was omitted.

Phagocytosis of Streptococcus uberis by bovine mammary gland macrophages

The ability of macrophages isolated from the bovine mammary gland to phagocytose and kill Streptococcus uberis was investigated. The strains of S uberis used were selected on the basis of their known resistance (C197C) or sensitivity (EF20) to phagocytosis by bovine peripheral blood neutrophils in the same assay system. Macrophages isolated from mammary secretions collected during the mid-dry period were capable of phagocytosing both strains of S uberis in the presence of serum and skimmed milk. The removal of complement from serum by heat-inactivation did not influence the opsonization of S uberis for phagocytosis by mammary macrophages and both IgG1 and IgG2 isotypes were found to opsonise both strains. The uptake of S uberis into the cells was confirmed by electron microscopy. Potential mechanisms by which S uberis could resist phagocytosis by neutrophils but not by macrophages are discussed.

Local vaccination with killed Streptococcus uberis protects the bovine mammary gland against experimental intramammary challenge with the homologous strain

The ability of killed streptococcus uberis to induce protection against mastitis when administered either into the cistern of the dry mammary gland (intramammary vaccination) without adjuvant or subcutaneously with adjuvant was investigated. Bacteria were never reisolated from vaccinated quarters following challenge with the same strain during the subsequent lactation, and no inflammatory response was detected. In contrast, following subcutaneous vaccination, milk from challenged quarters contained very small numbers of bacteria, but these quarters did exhibit clinical disease, whereas quarters on nonvaccinated control animals produced discolored, clotted secretion with large numbers of bacteria and somatic cells and required antibiotic therapy by 60 h postchallenge. There was a significant increase in the levels of S. uberis-specific immunoglobulin G1 (IgG1), IgG2, and IgM in milk following intramammary vaccination and in the levels of specific IgG1 and IgG2 in milk following subcutaneous vaccination. Levels of specific antibody in serum were also elevated following vaccination by either route. However, despite this, there was no increase in the opsonic activity of serum or milk. Both peripheral blood lymphocytes and dry-period mammary gland lymphocytes showed strong proliferative responses to S. uberis in vitro following subcutaneous vaccination, but only mammary gland lymphocytes responded following intramammary vaccination. It was concluded that the protection seen in vaccinated quarters did not appear to be related to levels of specific antibody or neutrophil function and was possibly brought about by the inhibition of bacterial growth.

Effect of cationization on anti-hapten antibody responses in sheep and mice

The effect on anti-hapten immune responses of altering the isoelectric point of hapten-carrier conjugates by cationization was examined in sheep and mice. No adjuvants were employed in these studies. In sheep the cationization of ovalbumin-dinitrophenyl (OVA-DNP) resulted in an enhanced primary anti-dinitrophenyl (DNP) response. The secondary anti-DNP responses were not consistently greater for animals primed with cationized (CAT) OVA-DNP than in animals primed with OVA-DNP. Similar results were obtained with mice immunized with bovine serum albumin (BSA)-DNP or CAT BSA-DNP. Mice and sheep primed with OVA-DNP failed to mount an anamnestic response following secondary immunization with CAT OVA-DNP. Failure of a cationized hapten-carrier to stimulate a secondary anti-DNP response following priming with uncationized hapten-carrier was also observed in mice using BSA-DNP as the model antigen.

Effect of a Staphylococcus aureus bacterin on serum antibody, new infection, and mammary histology in nonlactating dairy cows

The influence of a Staphylococcus aureus mastitis vaccine on immunologic status and rate of new IMI was evaluated. At drying off, cows were vaccinated, either intramuscularly or subcutaneously in the area of the supramammary lymph node, or were left as unvaccinated controls; vaccinates received booster injections at 6 wk. Serum antibody concentrations, bacteriologic status, and SCC of quarter milk samples were determined. Four weeks after revaccination, cows were challenged by intramammary infusion of S. aureus and then killed 24 to 72 h later. Mean serum antistaphylococcal antibody titer of vaccinated cows during the trial was 4.7-fold that of controls. Challenge resulted in IMI rates of 92, 36, and 60% for control cows, cows vaccinated intramuscularly, and cows vaccinated in the area of the supramammary lymph node. Vaccination by either route had no influence on mammary parenchymal tissue components compared with controls; however, leukocyte infiltration was greater in quarters from cows vaccinated in the area of the supramammary lymph node than in quarters from unvaccinated controls. Plasma cell populations producing IgG1, IgG2, IgA, and IgM were greatest in quarters of cows vaccinated in the area of the supramammary lymph node followed by those in quarters of cows vaccinated intramuscularly and control cows.

Killing of Streptococcus uberis by bovine neutrophils following growth in chemically defined media

Following growth in a chemically defined medium (CDM), five strains of Streptococcus uberis were tested for their ability to survive killing by bovine neutrophils. Strains 0140J, ST10, EF20 and C221 were easily killed, whereas strain C197C was highly resistant. The ability of strain 0140J to resist phagocytosis and killing was increased by supplementation of the growth medium with milk whey, casaminoacids, casein, or, to a lesser extent, bovine serum. Supplementation of the growth medium with yeast extract or bovine serum albumin did not affect the resistance of this strain. Following growth in CDM supplemented with casein, strains ST10 and C221, like strain 0140J, were significantly more resistant to killing by neutrophils. The resistance of strains EF20 and C197C was unaffected by the addition of casein to the medium; strain EF20 remained susceptible and strain C197C highly resistant to killing. The effect of supplementing the growth media with components other than casein was only studied for strain 0140J. Decapsulation of strains C197C, ST10 and 0140J, grown in CDM + casein, with type-X hyaluronidase did not significantly affect their ability to survive in the presence of bovine neutrophils.