Pathogenicity, haematology and pathology of Listeria monocytogenes in rat

Listeria monocytogenes is a gram positive bacterium of public health concern with low morbidity but high mortality rate. Listeriosis in human is usually caused by the consumption of infected animal and food. It is noteworthy that an infected animal such as rat could be potential carrier and vector. Therefore, this study examined the clinic pathological changes associated with Listeria monocytogenes infection in rat. Six (6) Winstar laboratory rats divided into 2 groups. Group 1 was challenged with 0.1-mL saline water as control while the second group was challenged intraperitoneally with 0.1 mL molecularly characterised Listeria monocytogenes (1 × 10⁴ CFU/mL) isolates. The rats were observed for clinical signs and mortality. Haematology, serum and enzymes indices were examined using standard procedures. Then, the liver and kidney of the rats from the two groups were aseptically examined for histopathological changes. The result shows that 33.3% of the rats challenged with Listeria monocytogenes died within 24 h (1 day) while 100% mortality were recorded within 48 h (2 days). There were significant decreases (P < 0.05) in the values of haematological parameters and biochemical of the rats than the control group (P < 0.05) while a significant increase in hepatic and renal blood enzymes of infected rats was observed. The rat exposed to Listeria infection revealed moderate glomerular atrophy in the kidney, and zonal degeneration of hepatocytes was observed in the liver. The study indicates that Listeria monocytogenes is a pathogenic organism to rats which could cause huge mortality within 3 days post infection. The infection also causes derangement of haematological, biochemical and tissue pathological changes in organs especially liver.