Studies of Listeria monocytogenes (Bacterium) in Some Selected Local Government Areas of Plateau State, Nigeria

Abstract

Studies were carried out on the distribution, characterization, pathogenicity and antibiotic susceptibility of Listeria monocytogenes in Six Local Government Areas of Plateau State, Nigeria. A total of One hundred and fifty (150) experimental samples were taken from each test Local Government Area. The isolation was carried out with the aid of cold enrichment, selective broth and selective Listeria agar. The experimental samples examined included: cow, goat, poultry, rabbit and sheep wastes (faecal samples). The other samples investigated included: cultivated soil particles, farm wastes, human wastes (faeces), decaying leaves and water. A total of nine hundred samples were examined in all. Out of these, 189 (21%) were found to contain Listeria species which was found to be highly significant at 5% and 10% level of probability (P = 0.01; P = 0.05). The Listeria isolates included L. monocytogenes (41.3%), L. ivanovii (20.1%), L. grayi (14.3%), L. welshimeri (8.4%), L. innocua (6.9%), L. murrayi (5.8%) and L. seeligeri (3.2%).The molecular characterization of the various L. monocytogenes isolates through polymerase chain reaction (PCR) technique into serotypes, revealed that they belonged to 13 serotypes (serovars). Listeria species occurrences were found to be highest in rabbit wastes (33.3%), followed by sheep wastes (27.8%), farm debris (23.3%), soil samples (22.4%), cow waste (22.2%), poultry droppings (20.0%), leaves (17.8%) and then water (13.3%). Samples of Human wastes were found to contain the least percentage of Listeria species (11.1%). It was observed that temperature, pH range and moisture content affected the colonization of the experimental samples by Listeria. The polymorphic nature but peculiar morphological characteristics of Listeria monocytogenes were helpful in the identification of the organism. The other species of microorganisms isolated along with Listeria monocytogenes during the studies included; Bacillus species, Brochothrix species, Kurthia species, Staphylococcus aureus, Streptococcus species, Candida albicans, Candida species, Aspergillus species, Mucor species and Penicilium species. Oxford Listeria agar was observed to favour the isolation and molecular characterization of the Listeria species. The data generated from the various experimental samples were subjected to statistical analyses. The results showed that the occurrence of L. monocytogenes and other Listeria species in the experimental specimens was significant at 5% and 10% level of probability (P = 0.01; P = 0.05). The results also showed that the employment of different culture media for the isolation of L. monocytogenes and other Listeria species was significant at 5% and 10% level of probability (P = 0.01; P = 0.05). The results of the pathogenicity study of L. monocytogenes 4b isolate in immunocompromised albino mice revealed that the organism could infect mice which could subsequently lead to their death. The necropsy examinations of visceral organs of such infected mice, revealed gross pathological and diagnostic features that are known to be peculiar to listerial infection. The L. monocytogenes 4b isolate was sensitive in-vitro to Gentamycin, followed by Ampicillin and then Penicillin. Others were Enrofloxacin followed by Neomycin, Oxytetracycline and then Keproceryl. The L. monocytogenes 4b organism was resistant to Pefloxacin only. The results obtained from the studies would serve as a valuable resource baseline for listeriosis surveillance in the study areas in particular and Nigeria in general. The public health implications of the various results obtained have also been discussed.