Safety and efficacy testing of a novel multivalent bovine bacterial respiratory vaccine composed of five bacterins and two immunogens.

Bovine bacterial respiratory diseases have been one of the most serious problems due to their high mortality and economic loss in calves. The vaccinations of bovine bacterial respiratory vaccines have been complex because of no multivalent vaccine. In this study, novel multivalent bovine bacterial respiratory vaccine (BRV) was developed and tested for its safety and efficacy. BRV was composed of two immunogens and five bacterins. These were leukotoxoid and bacterin of Mannheimia haemolytica type A, outer membrane protein and bacterin of Pasteurella multocida type A, and bacterins of Haemophilus somnus, Mycoplasma bovis, and Arcanobacterium pyogenes. ELISA antibody titers to five bacterial antigens in vaccinated guinea pigs increased, compared with those in unvaccinated ones. BRV was safe for calves and pregnant cattle in this study. In calves challenged with M. haemolytica and P. multocida, the average daily weight gain and antibody titers of vaccinated calves increased, and respiratory symptoms (P<0.05) and treatment frequency (P<0.01) of vaccinated calves significantly decreased, compared with those of unvaccinated calves. Interestingly, the antibody titers of M. haemolytica leukotoxoid and Mycoplasma bovis were closely related with the reduction of respiratory symptoms. BRV would be an ecomonical measure for the protection against bovine bacterial respiratory diseases.

Isoleucine 61 is important for the hemolytic activity of pyolysin of Trueperella pyogenes.

Pyolysin (PLO) is a hemolysin secreted by Trueperella pyogenes (T. pyogenes) and is important for the pathogenicity of T. pyogenes. Oligomerization of PLO monomers is a critical step in the process of hemolysis. However, the mechanisms of intermolecular interaction of PLO monomers are still not clearly illuminated. In this study, two monoclonal antibodies (mAbs) against PLO, named AP-1A3 and AP-4F12, respectively, were generated firstly, of which AP-1A3 showed no or undetectable hemolysis inhibition activity against recombinant PLO (rPLO), whereas AP-4F12 could markedly inhibit the hemolytic activity of rPLO. Epitope mapping revealed that AP-1A3 recognized amino acid residues ranging from 64 to 79 of mature PLO (91-106 including the signal peptide), whereas AP-4F12 recognized amino acid residues ranging from 58 to 75 (85-102 including the signal peptide). Comparison of the amino acid sequence of two epitopes revealed that six amino acid residues ranging from 58 to 63 of PLO were associated with the hemolytic activity of PLO. Alanine scan showed that substitution of each amino acid ranging from 58 to 62 with alanine had apparent impact on the hemolytic activity of rPLO, especially for the substitution of isoleucine 61 which caused almost complete loss of hemolytic activity of rPLO. Our findings identified a region in PLO and an amino acid in that region might play important role in the process of oligomerization of PLO monomers.

Koch's postulate of Arcanobacterium pyogenes and its immunogenicity in local and imported Saanen goats.

The aim of this survey was to study Koch's postulate of Arcanobacterium pyogenes recovered from the necrotic lung of a kid and to compare the immunogenicity of this isolate in local and imported Saanen goats. The disease was successfully reproduced in intrathoracically challenged hamsters which showed lung congestion and liver abscesses, while hamsters that were intraperitoneally challenged showed only the formation of intestinal abscesses. The percentage of histopathologic legions in 12 observed microscopic fields per lung of three groups of hamsters (unchallenged controls, challenged intrathoracically and challenged intraperitoneally) showed a significant increase in lung necrosis of the intrathoracically challenged group, followed by intraperitoneally challenged hamsters, in comparison to unchallenged controls (p<0.05). In addition, the frequency of mucus accumulation in alveolar ducts followed the same respective pattern (p>0.05), while there was no significant difference in the frequency of neutrophil infiltration (p>0.05). The isolate was successfully recovered from the lungs and livers of hamsters challenged by both routes. Saanen does showed significant seroconversion using the indirect haemagglutination (HA) test and slide agglutination test (SAT) and at three weeks following priming and boosting with A. pyogenes antigens (p<0.05); however, only SAT showed significant seroconversion in local does at three weeks post booster (p<0.05). The possible causes and impact of the greater immunogenicity to A. pyogenes antigens in Saanen goats compared to local does are discussed.