Abstract:
Listeriosis is a disease of humans and animals, in which it is one of the important emerging
bacterial zoonotic diseases worldwide. Among the different species of Listeria, Listeria
monocytogenes is the most common causes of Listeriosis in humans and animals, as a result of food
and environmental contamination with low incidence but high case fatality rate. The present study
was undertaken to isolate Listeria species in raw bovine milk. A cross-sectional study was
conducted from January to September 2015 to determine the presence of Listeria monocytogenes
and other Listeria species from raw milk samples originated from dairy producers and vendors and
determining antimicrobial resistance profile of Listeria monocytogene. A total of 407 raw milk
samples of which, 384 from dairy producers were collected by using simple random sampling
technique and 23 from vendors were also collected. Listeria species isolations were performed
according to the standard bacteriological techniques by using Listeria enrichment broth, Modified
Fraser broth and Oxford Agar medium as well as comfirmatory tests: carbohydrate utilization
(rhamnose, xylose, mannitol); blood agar (hemolysis) and Christie Atkins Munch Peterson (CAMP)
test. The antimicrobial resistance profile of Listeria monocytogenes was also assessed by using the
standard disk diffusion method (Kirby Bauer techniques) and it was tested against 9 antimicrobial
drugs (Cephalothin 30µg, Chloramphenicol 30µg, Kanamycin 30µg, Nalidixic acid 30µg,
Streptomycin 10µg, Tetracycline 30µg, Vancomycin 30µg, Gentamicin 10µg and Ampcillin 10µg).
Overall isolated Listeria species were Listeria monocytogenes 36 (8.84%), Listeria innocua 28
(6.88%), Listeria seeligeri 14 (3.4%), Listeria grayi 3 (0.74%), Listeria welshimeri 2 (0.49%) and
Listeria murrayi 2 (0.49%). Antimicrobial susceptibility test was conducted on 36 isolated Listeria
monocytogenes. Listeria monocytogenes were found to be resistant to two or more antimicrobial.
The presence of Listeria monocytogenes in raw milk and drug resistant isolates of the bacteria is an
indication of public health hazards to the consumers, particularly to the high risk groups. Hence
awareness creation on milk safety and implementations of regulations about the use of
antimicrobials in humans and animals should be strongly practiced.
