The problem of immunization against staphylococcal mastitis

Progress towards the Elusive Mastitis Vaccines

Mastitis is a major problem in dairy farming. Vaccine prevention of mammary bacterial infections is of particular interest in helping to deal with this issue, all the more so as antibacterial drug inputs in dairy farms must be reduced. Unfortunately, the effectiveness of current vaccines is not satisfactory. In this review, we examine the possible reasons for the current shortcomings of mastitis vaccines. Some reasons stem from the peculiarities of the mammary gland immunobiology, others from the pathogens adapted to the mammary gland niche. Infection does not induce sterilizing protection, and recurrence is common. Efficacious vaccines will have to elicit immune mechanisms different from and more effective than those induced by infection. We propose focusing our research on a few points pertaining to either the current immune knowledge or vaccinology approaches to get out of the current deadlock. A possible solution is to focus on the contribution of cell-mediated immunity to udder protection based on the interactions of T cells with the mammary epithelium. On the vaccinology side, studies on the orientation of the immune response by adjuvants, the route of vaccine administration and the delivery systems are among the keys to success.

Vaccination strategies for reducing clinical severity of coliform mastitis

Brief history and extensive published field efficacy data of the two rough ("R") bacterial mutants utilized in commercial preparations of the core antigen bacterins Escherichia coli O111:B4 (strain J5) and Salmonella typhimurium Re-17 are summarized. Particular dosage schedules and routes of administration of coliform mastitis bacterins are compared for their associated ecacy. Practical concerns in employing a coliform mastitis vaccination program are discussed. Characteristics of farms using coliform mastitis vaccination and suggested guidelines for whether individual dairy herds should adopt this practice are presented for consideration.

Immunisation of dairy cattle with recombinant Streptococcus uberis GapC or a chimeric CAMP antigen confers protection against heterologous bacterial challenge

The gapC genes, encoding the cell surface-associated GapC proteins of S. uberis and S. agalactiae, have been cloned and sequenced. To identify potential vaccine candidates against S. uberis-induced bovine mastitis, lactating dairy cows were vaccinated with either (6 x His)GapC of S. uberis or S. dysgalactiae, or with a chimeric CAMP-factor antigen, CAMP-3. For 7 days following heterologous challenge with S. uberis, milk somatic cell counts were determined to assess differences in the severity of mastitis between vaccinates and an unvaccinated control group. Vaccination with S. uberis (6 x His)GapC or CAMP-3 resulted in a significant reduction in inflammation on several days post-challenge, most significantly for the former antigen. Inflammation was not reduced in S. dysgalactiae (6 x His)GapC vaccinates, suggesting that it does not confer cross-species protection.

Vaccines and diagnostic methods for bovine mastitis: fact and fiction

A number of problems are uniquely associated with vaccination of dairy cows for mastitis. One of these is that the number of mastitis pathogens is numerous and heterogeneous. Vaccine efforts have concentrated mainly on the major mastitis pathogens. While at least one S. aureus bacterin has been commercially available for a number of years, no large-scale, independent field trials have been published in refereed journals which support the efficacy of this vaccine. Experimental vaccines for S. aureus composed of pseudocapsule-enriched bacterins supplemented with alpha- and/or beta-toxoids appear promising, but none of these has been commercialized. With S. uberis, some protection against homologous strain challenges was reported recently with a live strain and a bacterin, but other data from the same laboratory showed this vaccine would not protect against heterologous challenge strains. At this time there is only one highly effective vaccine for mastitis, the core-antigen vaccine for coliform mastitis. All of the commercially available vaccines for this indication are bacterins of rough mutants of E. coli strain J5 or Salmonella spp. Preliminary success with an experimental vaccine based on the plasminogen activator of S. uberis is a very different approach for a mastitis vaccine. Little success has been reported with vaccination against other mastitis pathogens. For diagnostic methods, the high somatic cell count, as measured by direct count or indirect assays, remains the cornerstone of mastitis diagnosis. However, for subclinical mastitis, bacterial cell culture is a reliable diagnostic method. Pathogen identification may rely on older biochemical testing methods or newer commercial identification systems, depending on the laboratory budget. ELISA assays also have been used to assess herd infection status. Epidemiologic studies have used DNA fingerprinting and ribotyping, but none of these methods has yet produced an easily utilized commercial format. Within the next decade, additional efficacious vaccines for several of the most common agents for bovine mastitis are likely. A review written at that time then can be more fact than fiction.

Effects of autogenous toxoid-bacterin in lactating cows with Staphylococcus aureus subclinical mastitis

To evaluate clinical effects of autogenous toxoid-bacterin treatment for Staphylococcus aureus subclinical mastitis in lactating cows, 22 cows which had at least one S. aureus infected quarter were selected from among cows at a S. aureus prevalent dairy farm. Eleven cows were injected with their own autogenous toxoid-bacterin and the others were maintained as non-injected control. In the toxoid-bacterin injected group, 27% of infected quarters were cured during the 12-week trial, compared to 5% in the control group. New intramammary infections with S. aureus were only detected in 3 quarters of the control group. Mean IgG antibody titer against S. aureus somatic antigens and alpha-toxin in serum and milk were significantly increased in the toxoid-bacterin injected group (p<0.05) and remained higher than those of the control group which showed no significant changes (p<0.05). In contrast to the control group, from 3 weeks after the second injection of the toxoid-bacterin injected group, mean S. aureus cfu/ml in milk samples from injected quarters with S. aureus was significantly decreased until the end of the study (p<0.05). In the toxoid-bacterin injected group, significant decreases of mean SCC were detected from milk samples from infected quarters with S. aureus from week 7 to week 10 (p<0.05). These data show that autogenous toxoid-bacterin treatment against S. aureus subclinical mastitis in lactating cows may increase the cure rate of the infections, reduce the severity of the infections and also prevent occurrence of the new infections.

Immune recruitment and bactericidal activity of neutrophils in milk of cows vaccinated with staphylococcal alpha-toxin

The ability of Staphylococcus aureus alpha-toxin to recruit neutrophils in the milk of vaccinated cows and the bactericidal efficiency of these neutrophils were evaluated. Six lactating Holstein cows that were free of intramammary infection received systemic immunization by subcutaneous injection of Freund's incomplete adjuvant with alpha-toxin (n = 2), alpha-toxin mixed with type 5 capsular polysaccharide (n = 2), or a conjugate of these two antigens (n = 2). Controls (n = 4) and vaccinated cows (n = 6) received intramammary infusions of alpha-toxin. No increase in somatic cell count was recorded in quarter milk samples from unimmunized cows; however, 10 micrograms of alpha-toxin induced a local inflammatory reaction in vaccinated cows that was characterized by early and massive cellular recruitment into the mammary gland. More than 90% of the recruited cells were neutrophils. The speed and magnitude of the cellular recruitment were dose-dependent; the threshold dose was 0.6 microgram. Milk samples showed significant bactericidal activity against the type 5 S. aureus strain, regardless of the vaccine used, and showed a decrease in bacterial count of about 2 log10 from the initial inoculum. The best efficiency was recorded during the early phase of cellular recruitment with concomitant activation of blood-derived neutrophils. This study demonstrates that a bacterial virulence factor, alpha-toxin, is able to induce immune recruitment of neutrophils for efficient bactericidal activity in milk when cows are immunized with alpha-toxin that is used either as a nonconjugate vaccinate or as a carrier protein in a conjugate vaccine. The study also suggests that neutrophils that are recruited from blood are activated during inflammation in response to specific antigens.

Field trials of a vaccine against bovine mastitis. 2. Evaluation in two commercial dairy herds

A vaccine against bovine mastitis was developed. The vaccine was based on inactivated, highly encapsulated Staphylococcus aureus cells; a crude extract of Staph. aureus exopolysaccharides; and inactivated unencapsulated Staph. aureus and Streptococcus spp. cells. In this study, the vaccine was evaluated in 164 cows from two commercial dairies (A and B) during a 4-mo period. Two doses of the vaccine were administered subcutaneously to 82 cows in the brachiocephalicus muscle of the neck within a 4-wk interval. The results of this trial revealed significantly fewer intramammary infections caused by Staph. aureus at various levels of severity (clinical, subclinical, and latent) in cows that were vaccinated. The odds ratios of all types of intrammammary infections caused by Staph. aureus for dairies A and B, which were determined by a logistic model, were 1.84 and 1.89, respectively, for quarters of vaccinated cows and quarters of control cows. The colony counts for Staph. aureus in milk from infected quarters of vaccinated cows were significantly lower than those in milk from infected quarters of control cows. Also, the somatic cell counts per milliliter in milk from vaccinated cows were significantly decreased when the initial somatic cell count was < 500,000 cells/ml at the start of the trial. The vaccine had no observable effect on fat production in milk or on streptococcal infections.

A field trial with an experimental vaccine against Staphylococcus aureus mastitis in cattle. 1. Clinical parameters

A total of 108 heifers were included in a placebo-controlled multicenter study on the use of an experimental Staphylococcus aureus mastitis vaccine containing whole, inactivated bacteria with pseudocapsule, alpha and beta toxoids, and a mineral oil as adjuvant. The heifers were injected in the area of the supramammary lymph nodes twice before calving and were observed and sampled throughout the first lactation. None of the vaccinated cows suffered from clinical Staph. aureus mastitis, and only 8.6% suffered from subclinical Staph. aureus mastitis, but a total of 16.0% of the control cows suffered from clinical or subclinical Staph. aureus mastitis. Mean SCC in vaccinated and control cows were the same throughout the lactation. Local swellings at the injection site were palpable in a substantial proportion of the vaccinated cows. In the statistical analyses, when cow was used as the unit of concern, no significant differences occurred between groups. However, when all parameters on udder health were considered together, the results indicated a potential protective effect of this vaccine during the entire lactation.

Recent advances in bovine vaccine technology

A description of new commercial and experimental vaccines for viral and bacterial diseases of cattle can be broadly divided into those used for both beef and dairy cows and those used predominantly in dairy cattle. For both types of cattle, newer and experimental vaccines are directed against several of the important viral (e.g., bovine herpesvirus 1, bovine viral diarrhea virus, bovine respiratory syncytial virus, parainfluenza type 3, and foot-and-mouth disease virus) and bacterial pathogens (e.g., Pasteurella spp., Haemophilus somnus). The viral vaccines include gene-deleted, modified live, subunit, and peptide antigens. Newer bacterial vaccines, particularly those for Pasteurella spp., are composed of either modified-live vaccines or bacterins supplemented with toxoid or surface antigens. Haemophilus somnus vaccine research has concentrated mainly on defining unique surface antigens. Novel dairy cow vaccines would include the lipopolysaccharide-core (J5) antigen approach, which has been used for successful immunization against coliform mastitis. Core antigen vaccines also have reduced calf mortality from Gram-negative pathogens. Staphylococcal mastitis vaccines that contain capsular antigens, toxoids, or the staphylococcal fibronectin receptor are of active research interest. Vaccines against mastitis induced by Streptococcus agalactiae and Streptococcus uberis also are areas of intensive research. Delivery of multiple subunit antigens with optimal immune response induction has led to the investigation of attenuated heterologous viral and bacterial expression vectors such as bovine herpesvirus 1, vaccinia, and Salmonella spp. This discussion also demonstrates that molecular biology is being used to advance bovine vaccine technology.

Vaccination against experimental staphylococcal mastitis in dairy heifers

Vaccination-challenge experiments were carried out with dairy heifers using new, killed cell-toxoid-adjuvant Staphylococcus aureus vaccines. The organisms in the vaccines were cultured under conditions which simulated in vivo growth and induced expression of a pseudocapsule. Dextran sulphate which promotes synthesis of IgG2 antibody was included in the vaccines as the primary adjuvant. Vaccinated heifers developed very high levels of both IgG1 and IgG2 anti-pseudocapsule antibody in serum, however, titres of neutralising antibody against toxoided haemolysins were generally low. Vaccinated and unvaccinated control heifers were challenged by intramammary infusion of three virulent strains of S aureus in four experiments. Vaccinated heifers were more resistant to clinical mastitis following challenge than were controls, and the vaccinates had significantly greater milk production than controls following challenge. The most promising vaccine had dextran sulphate combined with mineral oil as the adjuvant injected intramuscularly.

Potential for vaccination against infections caused by Staphylococcus aureus

Surface polysaccharides and proteins from S. aureus which could serve as components of a future subunit vaccine against staphylococcal disease in man and animals have recently been characterized. The majority of bovine mastitis and human clinical isolates of S. aureus produce a thin polysaccharide capsule which probably impairs phagocytosis. Protective immunity to S. aureus infections in laboratory animals has been induced by immunization with polysaccharide, and immune serum promotes phagocytosis of bacteria in vitro. S. aureus expresses several surface-exposed proteins that bind host plasma proteins to the bacterial cell or promote adherence of bacteria to host cells or to tissues. These activities may help bacteria avoid host defences and stimulate adherence and colonization to form foci of infection. In this article the properties of S. aureus surface polysaccharides and proteins are reviewed. Their contribution to virulence and the possibility that they could be used as components of new vaccine to combat mastitis in ruminants and nosocomial infections is discussed.

Synergism between antibody and neutrophils in the ruminant mammary gland

Immunological activities of the mammary gland are important both as a means of transferring immunity from mother to young and for defending the mammary gland itself against infection. The presence of immunoglobulins G1, G2 and A, and of neutrophils, macrophages and complement in the ruminant mammary gland is described, in particular the synergistic role of antibody and neutrophils is discussed and studies of immunization against staphylococcal mastitis are outlined.

Evaluation of protein A and a commercial bacterin as vaccines against Staphylococcus aureus mastitis by experimental challenge

Protein A and a commercial staphylococcal bacterin were evaluated by experimental challenge with Staphylococcus aureus (ATCC 29740). Thirty cows in first lactation were in three treatment groups, protein A, bacterin, and nonvaccinated controls. Studies were through three lactations and included bacteriological and cytological analyses of quarter milk samples. Rate of intramammary infection with Staphylococcus aureus was similar for vaccinated and unvaccinated cows. Rates of spontaneous cure within each lactation were significantly higher for vaccinated cows. For all three lactations, spontaneous cure rates were 83, 73, and 47% for protein A, bacterin, and control cows. Somatic cell counts were significantly lower for vaccinated cows for quarters infected with Staphylococcus aureus, but no differences were demonstrated for milk production by lactation. Incidence of clinical mastitis was higher in unvaccinated cows, but too few developed for a valid comparison.