Stability, antigenicity, and aggregation of Moraxella bovis cytolysin after purification and storage

Recombinant Moraxella bovoculi cytotoxin-ISCOM matrix adjuvanted vaccine to prevent naturally occurring infectious bovine keratoconjunctivitis

A randomized, blinded, controlled field trial was conducted during summer 2006 in a northern California, USA, herd of beef cattle to evaluate the efficacy of a recombinant Moraxella bovoculi cytotoxin subunit vaccine to prevent naturally occurring infectious bovine keratoconjunctivitis (IBK; pinkeye). A convenience sample comprised of 127 steers were administered a subcutaneous dose of either adjuvant alone (ISCOM matrices; control group) or recombinant M. bovoculi cytotoxin carboxy terminus adjuvanted with ISCOM matrices (MbvA group) and were boostered 21 days later. The steers were examined once weekly for 15 weeks for evidence of IBK. No significant difference in the cumulative proportion of corneal ulcerations was detected between groups. Compared to the control calves, the MbvA vaccinates had significantly higher increases in serum neutralizing titers to M. bovoculi hemolysin between week 0 and week 6. The prevalence of M. bovis isolations was higher from ulcerated eyes of calves vaccinated with MbvA as compared to control calves. Vaccination of calves against the carboxy terminus of M. bovoculi RTX toxin resulted in significant increases in serum hemolysin neutralizing titers and may modulate organism type cultured from ulcerated eyes of calves in herds where both M. bovis and M. bovoculi exist. Use of M. bovoculi antigens alone in vaccines to prevent IBK may not be beneficial in herds where IBK is associated with both M. bovoculi and M. bovis.

Relatedness of cytotoxins from geographically diverse isolates of Moraxella bovis

To determine whether amino acid sequence variation exists in the Moraxella bovis (M. bovis) cytotoxin (MbxA) from geographically diverse M. bovis isolated in the United States, mbxA was amplified and sequenced. The MbxA deduced amino acid sequence from M. bovis originally isolated in California, Washington, North Carolina, and Georgia, as well as reference strains of M. bovis isolated at the National Animal Disease Laboratory, Ames, IA, USA, all encoded a nearly identical 927 amino acid protein. MbxA from two of the four California isolates (SFS 9a and SFS 100a) differed from all other isolates at two sites at which the polar amino acids glutamine (position 666) and asparagine (position 823) were replaced by ionized amino acids glutamic acid and aspartic acid, respectively. Rabbit antiserum to the expressed carboxy terminus (amino acids 590-927) of MbxA from M. bovis (Tifton I) neutralized the hemolytic activity of SFS 9a and SFS 100a. The M. bovis cytotoxin appears to be conserved amongst geographically diverse isolates of M. bovis from the USA. Antiserum against the carboxy terminus of MbxA common to the majority of isolates neutralized the hemolytic activity of two strains with a divergent MbxA deduced amino acid sequence. Vaccines against IBK that incorporate MbxA as antigen may offer protection against geographically diverse strains of M. bovis.

Infectious bovine keratoconjunctivitis vaccine development

Infectious bovine keratoconjunctivitis is a common and highly contagious ocular disease affecting cattle worldwide. The tremendous economic losses attributable to this disease warrant continued investigation into methods of prevention. Multiple virulence factors have been linked to the primary aetiologic agent, Moraxella bovis. Efforts to develop an efficacious vaccine have primarily focused upon the use of surface pili or cytolysin to stimulate host immunity; however, M. bovis possesses other virulence determinants that include proteases, fibrinolysins, phospholipases and other cell surface components such as outer membrane proteins. These potentially conserved antigens provide additional possibilities for vaccine development. Examination of appropriate antigen presentation is necessary to attain an adequate immune response. Further, the potential for antigenic diversity as well as epitope conversion requires continuous epidemiological surveillance of isolates recovered from outbreaks. Current work targeting conserved immunogens provides hope for efficacious vaccines that when used in tandem with proper management may control, if not prevent, infectious bovine keratoconjunctivitis.

Effectiveness of a cytolysin-enriched vaccine for protection of cattle against infectious bovine keratoconjunctivitis

OBJECTIVE

To determine the immunogenicity of a Moraxella bovis cytolysin-enriched vaccine for prevention of infectious bovine keratoconjunctivitis (IBK).

ANIMALS

104 mixed-breed beef calves ranging between 4 and 8 months of age.

PROCEDURE

Vaccines were prepared by the diafiltration of broth culture supernatant from hemolytic M bovis or sterile media. The diafiltered retentate was combined with Quil A adjuvant. Calves were randomly assigned to receive either the cytolysin vaccine (n = 35) or, as controls, adjuvant (35) or saline (0.9% NaCl) solution (34). Eyes of all calves were examined weekly for signs of IBK for 15 weeks. Calves that developed severe IBK were treated SC with florfenicol.

RESULTS

Cytolysin vaccine contained 4 proteins with molecular masses ranging between 65 and 90 kd. Cytolysin-vaccinated calves had fewer instances of IBK than control calves. The time of onset of corneal lesions in cytolysin-vaccinated calves that developed IBK was delayed, compared with that of calves in either control group. The cytolysin-Quil A vaccine contained endotoxin, but calves did not have clinical signs of illness after vaccination.

CONCLUSIONS AND CLINICAL RELEVANCE

Calves that were vaccinated with a cytolysin-enriched vaccine had some resistance to IBK. Vaccines containing concentrated diafiltered M bovis cytolysin could protect beef calves against IBK.