Staphylococcal mastitis vaccine

Letter Staphylococcal mastitis vaccine The April 1991 issue of Vaccine included a review paper by Foster ~ which described some of the recent advances in knowledge of Staphylococcus aureus antigens. However, the review failed to mention the progress that has been made in gaining an improved understanding of immunity to S. aureus. The results of strategic research in this area have led to the development, in this laboratory, of a vaccine which is effective in controlling staphylococcal mastitis in ruminants. These important findings, many of which have now been confirmed in other laboratories around the world, are summarized herein : 1 It has been known for many years that live S. aureus vaccines, given subcutaneously, provide a considerable degree of protection from staphylococcal mastitis 2'3. This has been confirmed by studies in our laboratory 4'5. 2 Ruminant neutrophils bear membrane receptors for the Fc portion of IgG2 molecules 6. Following immunization with a live S. aureus vaccine, ruminants mount a strong IgG 2 anti-S, aureus antibody response 7. The IgG2 in plasma and on neutrophil membranes is in dynamic equilibrium. Neutrophils collected from ewes that have been immunized with a live S. aureus vaccine have enhanced capacity to phagocytose and kill S. aureus in in vitro assays, compared with neutrophils from nonimmunized ewes or from ewes immunized with a conventionally prepared, killed S. aureus vaccine s. This enhanced phagocytosis is entirely attributable to the presence of cytophilic IgG2 antibody on the neutrophil membrane 6`s. Conventionally prepared, killed S. aureus bacterin vaccines, with or without toxoids and with or without adjuvants, stimulate very poor IgG 2 antibody responses and provide little or no protection from staphylococcal mastitis 9- ~i. 3 Non-lactating ewes immunized systemically with a live S. aureus vaccine mounted an earlier and more pronounced inflammatory response in the udder (compared with non-immunized ewes) following an intramammary

challenge infection with S. aureus. The leucocytes involved in this early inflammatory response are predominantly neutrophilis 1~. 4 S. aureus cultured under in vivo conditions express additional cellsurface antigens when compared with in vitro-grown organisms of the same strain 13. In vivo-grown S. aureus are more virulent/pathogenic than their in vitro-grown counterparts 14. The 'in vivo antigens' are associated with a pseudocapsule (or glycocalyx). The pseudocapsule has been shown to be present on S. aureus in milk of cows suffering clinical staphylococcal mastitis aS. We have now developed bacteriological media and growth conditions ('simulated in vivo culture') which result in expression of the pseudocapsule during laboratory culture. 5 A critical hurdle to developing a practical vaccine based on the above principles was finding an immunological adjuvant which, when combined with S. aureus bacterin, would preferentially stimulate synthesis of IgG2 anti-staphylococcal antibody. It has now been established that dextran sulphate has these properties ~6. 6 A safe, efficacious vaccine against staphylococcal mastitis in ruminants has been developed. It provides a significant level of protection to lactating ewes iv and cows is. These discoveries are protected by international patents. Industrial partners in Australia and USA are developing the vaccine as a commercial product for ruminants. The failure of Foster's review to mention any of these developments or to cite any of this literature may have left many readers with an incomplete picture of present knowledge of immunity to S. aureus in ruminants and with misconceptions about the progress that has been made with vaccination against staphylococcal mastitis.

D.L. Watson C S I R O , Division o f A n i m a l H e a l t h , A r m i d a l e , N S W 2350, A u s t r a l i a

References 1 Foster, T.J. Potential for vaccination against infections caused by Staphylococcus aureus. Vaccine 1991, 9, 221 2 Bidrb, J. La mammita gangreneuse des brebis laitibres: pathogenic et vaccination. Bull. Soc. Cent. Mad. Vet. 1907, 61, 500 3 Derbyshire, J.B. The immunisation of goats against staphylococcal mastitis by means of experimental infections of the skin and udder. Res. Vet. Sci. 1961, 2, 112 4 Watson, D.L. and Lee, C.G. Immunity to experimental staphylococcal mastitis - comparison of live and killed vaccines. Aust. Vet. J. 1978, 54, 374 5 Watson, D.L. Evaluation of attenuated live staphylococcal mastitis vaccine in lactating heifers. J. Dairy Sci. 1984, 67, 2608 6 Watson, D.L. The effect of cytophilic IgG2 on phagocytosis by ovine polymorphonuclear leucocytes. Immunology 1976, 31, 159 7 Watson, D.L. The serological response in sheep to live and killed Staphylococcus aureus vaccines. Vaccine 1987, S, 275 8 Watson, D.L. Enhancement of in vitro phagocytosis of Staphylococcus aureus by polymorphonuclear leucocytes. Res. Vet. Sci. 1975, 19, 288 9 Watson, D.L. Ovine opsonins for Staphylococcus aureus cell wall and pseudocapsule. Res. Vet. Sci. 1989, 46, 84 10 McDowell, G.H. and Watson, D.L. Immunity to experimental staphylococcal mastitis: comparison of local and systemic immunisation. Aust. Vet. J. 1974, 50, 533 11 Watson, D.L. and Kennedy, J.W. Immunization against experimental staphylococcal mastitis in sheep effect of challenge with a heterologous strain of Staphylococcus aureus. Aust. Vet. J. 1981, 57, 309 12 Colditz, I.G. and Watson, D.L. Effect of immunization on the early influx of neutrophils during staphylococcal mastitis in ewes. Res. Vet. Sci. 1982, 33, 146 13 Watson, D.L. and Prideaux, J.A. Comparisons of Staphylococcus aureus grown in vitro or in vivo. Microbiof. ImmunoL 1979, 23, 543 14 Watson, D.L. Virulence of Staphylococcus aureus grown in vitro or in vivo. Res. Vet. Sci. 1982, 32, 311 15 Watson, D.L. and Watson, N.A. Expression of a pseudocapsule by Staphylococcus aureus influence of cultural conditions and relevance to mastitis. Res. Vet. Sci. 1989, 47, 152 16 Kerlin, R.L. and Watson, D.L. Effect of dextran sulphate on IgG subclass of antibody in efferent popliteal lymph of sheep. Immunol. Cell Biol. 1987, 65, 411 17 Watson, D.L. Vaccination against experimental staphylococcal mastitis in ewes. Res. Vet. Sci. "1988, 415, 16 18 Watson, D.L. and Schwartzkoff, C.L. A field trial to test the efficacy of a staphylococcal mastitis vaccine in commercial dairies in Australia. Proceedings of the International Symposium on Bovine Mastitis, Indianapolis, Indiana, USA, 1990, p 73

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