Studies on Pathogenicity of Pasteurella multocida Serotype B: 2 in Mice

In an experimental study, five field isolates of Pasteurella multocida recently isolated from natural sporadic cases from cattle were tested for their pathogenicity in mice. 0.2 ml of eighteen hours old broth cultures of each of the test isolates containing approximately 2.4×108 CFU/ml was inoculated into four mice (2 male and 2 female) by intra peritoneal route and two mice (1 male and 1 female) were kept as control and inoculated with Brain Heart Infusion (BHI) broth. All the mice died within 24 hours of inoculation. The presence of P. multocida in the dead mice was detected by smear examination followed by re-isolation of pure colonies on sheep blood agar (SBA) and was later confirmed by P. multocida specific polymerase chain reaction (PM-PCR). P. multocida was detected in all the dead mice. All the five isolates amplified KMT1gene and gave an amplified product of ~460 bp. Gross pathological changes comprised of mild congestion and haemorrhages in organs like lung, heart, kidneys, liver and spleen. Histopathological changes revealed congestion, haemorrhages along with fibrinous exudation in lung, haemorrhages, vascular congestion and varying degree of degenerative and necrotic changes in heart, sinusoidal congestion and hydropic degeneration in liver and congestion of intertubular capillaries in kidney.