Ultrastructural Changes and Bacterial Localization in Buffalo Calves Following Oral Exposure to Pasteurella multocida B:2

Abstract

This study describes the ultrastructural changes and distribution of P. multocida B:2 in the respiratory and gastrointestinal tracts of buffalo calves following oral exposure and compared with intratracheal exposure. Nine 8-month old buffalo calves were divided into 3 groups. At the start of the experiment, dexamethasone (1mg/kg) was injected intramuscularly into buffaloes of all groups for three consecutive days. Then, calves of Group 1 were exposed orally to 50ml of the inoculum containing 109 colony-forming unit (CFU)/mL of live P. multocida B:2. Calves of Group 2 were exposed intra-tracheal to the same inoculum while calves of Group 3 were exposed orally to PBS. Transient and mild clinical signs were observed in calves of Groups 1 and 2. Pasteurella multocida B:2 was isolated from the nasal mucosa for up to 5 days post-infection. Only calf that was killed at 48 h post-infection had P. multocida B:2 in both respiratory and gastro-intestinal tracts showing ultrastructural changes typical of acute cellular injury, with degeneration of endothelium and vascular walls. There were deciliation in the respiratory and microvilli degeneration in the gastrointestinal tracts. The study concludes that oral exposure may not play major role in the development of hemorrhagic septicemia. Nevertheless, the buffalo calf that succumbed to hemorrhagic septicemia carried P. multocida B:2 in the gastro-intestinal organs.