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Isolation, Identification and Antimicrobial Susceptibility of Listeria Species from Raw Bovine Milk in Debre-Birhan Town, Ethiopia

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 confirmatory 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 30 μg, Chloramphenicol 30 μg, Kanamycin 30 μg, Nalidixic acid 30 μg, Streptomycin 10 μg, Tetracycline 30 μg, Vancomycin 30 μg, Gentamicin 10 μg and Ampcillin 10 μg). 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. Therefore awareness creation on milk safety and implementations of regulations about the use of antimicrobials in humans and animals should be strongly practiced.

Author(s): Girma Y* and Abebe B

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