Characterization of the antibody isotype response in serum and milk of heifers vaccinated with a Staphylococcus aureus bacterin (Lysigin).

The objective was to characterize the antibody isotype responses to vaccination with a commercial Staphylococcus aureus bacterin in dairy heifers. Twenty-five Holstein-Friesian dairy heifers were assigned at random to one of two groups, vaccinates (n=14) or controls (n=11). Vaccinates received two 5-ml doses of Lysigin 28 d apart in late gestation. Both groups were challenged with a heterologous serotype 5 strain of Staph. aureus by aseptic intramammary infusion on days 6, 7 and 8 of lactation. Samples for serum antibody isotype (IgG, IgG1, IgG2 and IgM) determinations were taken before each vaccination, immediately prior to challenge (6 d post-calving) and at the end of the study (28 d post-calving). Samples for milk antibody isotype determinations were taken immediately prior to challenge and at the end of the study. Antibody isotype sample-to-positive ratios (S:P ratio=(mean test sample OD-mean within-plate negative control OD)/(mean within-plate positive control OD-mean within-plate negative control OD)) were determined in milk and serum using a series of ELISAs coated with different strains of Staph. aureus belonging to capsular polysaccharide (CP) serotype 5 or 8 or surface polysaccharide (SP) serotype 336. Vaccinates had higher mean serum IgG1 and IgG2 S:P ratios than controls against all three strains of Staph. aureus (P < or = 0.023). Vaccinates had higher mean milk IgG S:P ratios than controls against CP8 and SP336 strains of Staph. aureus (P< or = 0.030). Hence, a humoural immune response to the vaccine was detected in serum and milk, but responses varied according to strain and antibody isotype tested.

Efficacy of different Lysigin formulations in the prevention of Staphylococcus aureus intramammary infection in dairy heifers.

The objective was to compare the efficacy of two experimental Staphylococcus aureus mastitis bacterins and a currently marketed five-isolate-based Staph. aureus bacterin (Lysigin, Boehringer Ingelheim Vetmedica, Inc.) with unvaccinated controls. Forty-seven Holstein-Friesian heifers were randomly assigned to one of four groups such that Group 1 (n=11) received a three-isolate experimental bacterin, Group 2 (n=11) received a five-isolate experimental bacterin, Group 3 (n=14) received Lysigin, and Group 4 (n=11) served as unvaccinated controls. Vaccinations were administered twice 28 d apart in late gestation. All groups were challenged with a heterologous strain of Staph. aureus (ATCC 29740) on days 6, 7, and 8 of lactation. Mastitis score, somatic cell count (SCC), milk culture yield, and total daily milk yield data were collected before and after challenge. All 47 cattle developed a Staph. aureus IMI post-challenge with three animals in Group 1 and one animal in Group 3 clearing their Staph. aureus IMI by the end of the study. However, there was no evidence of a difference between vaccinates and control with regard to Staph. aureus clearance rates post-challenge (P> or =0.214). Cattle vaccinated with Lysigin had a lower mean duration of clinical mastitis and lower total mastitis score post-challenge than controls (P=0.045 and P=0.046, respectively). Overall, there was no evidence that any of the vaccinated groups had a lower mean SCC than control (P> or =0.148) for the tested study days. Likewise there was no evidence that vaccinates had greater milk yield than controls post-challenge (P=0.617). Hence, there was no evidence that the vaccines reliably prevented Staph. aureus IMI, but Lysigin showed benefit in reducing the clinical severity and duration of clinical disease post-challenge. Neither of the experimental bacterins appeared to perform better than Lysigin.