Evaluation of commercially available Escherichia coli J5 bacterin as protection against experimental challenge with Pasteurella multocida in rabbits

Objective - To evaluate the ability of commercially available Escherichia coli J5 bacterin to protect rabbits from experimental challenge with Pasteurella multocida. Animals - 40 P multocida-free New Zealand White rabbits. Procedures - Rabbits were assigned to 1 of 4 groups of 10 rabbits each. Three of the groups were inoculated SC with J5 bacterin at 8 weeks old. Inoculation was repeated 3 and 6 weeks later. The fourth group was not inoculated and served as controls. Groups 1, 2, and 3 were given 10⁹, 10⁸, and 10⁷ colony forming units (CFU), respectively. Response was monitored by titer assessment, using an E coli J5 antigen capture ELISA. Five weeks after the last inoculation, all rabbits were challenged with P multocida and observed for an additional 5 weeks. Clinical, hematologic, serologic, culture, and necropsy data were collected. Results - Inoculation of rabbits with 10⁹ CFU of E coli J5 bacterin-induced titers that were significantly greater than titers of rabbits vaccinated with 10⁸ or 10⁷ CFU or those in controls. The incidence of acute bacteremia was lower in rabbits with high titers. At necropsy, prevalence of lesions typical of P multocida was not significantly different among groups. Prevalence of histologic lesions was also not significantly different among groups. Conclusions and Clinical Relevance - Although the bacterin induced considerable antibody response and possibly reduced the rate of bacteremia, antibodies were not protective against long-term colonization or infection of the frontal sinuses or tympanic bullae by the challenge strain of P multocida. This bacterin in its currently available form is unlikely to aid in reducing the prevalence of pasteurellosis in rabbits.