Occurrence of Listeria monocytogenes in bovine milk

Bovine milk samples from Tandojam town, its surrounding farms and villages were collected and brought to the Central Veterinary Diagnostic Laboratory, Tandojam and also the Department of Microbiology, Faculty of Animal Husbandry and Veterinary Sciences, Sindh Agriculture University Tandojam and studied. A total of 100 milk samples, 50 each from cattle and buffaloes (25 mastitic, 15 non mastitic & 10 bulk cans) were collected and examined for the presence of Listeria monocytogenes In buffaloes, 24% mastitic 20% non-mastitic and 40% from bulk cans were found positive for Listeria monocytogenes while in cattle, 32% mastitic 13.33% non-mastitic and 20% from bulk milk cans were noted positive for the species. The present study also reveals that Listeria monocytogenes can be found in the bovine milk with various degree of mastitis or without mastitis and could be transmitted through milk from animal to man and also Morphologically Listeria monocytogenes was coccoid, regular short rods with 0.4-0.5u X 0.5-2u in size arranged singly but occasionally in short chains. The cells were gram-positive and motile. On blood agar, it produced beta- hemolytic colonies with grayish-white in colour, and convex, entire margin and circular in shape. While on nutrient agar, it formed 0.5-1.5 mm diameter with round, translucent, dew drop like, low convex with fine textured surface and entire margin colonies, however small colonies with the same colour of that MacConkey's medium were also observed during investigation. Biochemically, Listeria monocytogenes was negative for Simmon's citrate urease. Oxidase indole. H2S production and gelatin liquefaction, while positive for catalase, methyl red. Voges Proskauer and TSI sugars recorded as A/A (Acid slant acid butt and gas). Listeria monocytogenes fermented quickly and produced acid from different sugars such as glucose, lactose. mannitol, inositol, arabinose and raffinose however it fermented sucrose and maltose very, slowly. It did not produce any gas from any sugars during study. In this study, pathogenicity of the organism was also investigated in rabbit and mice through Anton's and inoculation tests respectively. Listeria monocytogenes caused keratocon junctivitis in rabbit while in mice, it caused necrotic foci in liver, spleen and kidneys. Antibiogram sensitivity of Listeria monocytogenes was carried-out with eight different antibiotics. The antibiotics used were; gentamycin, tetracycline, erythromycin ampicilin, kanamycin, neomycin, penicillin and sulpha methoxazole. Among these antibiotics: gentamycin (96%) tetracycline (92%), ampicilin (92%) and kanamycin (96%) were round highly effective against the Listeria monocytogenes.