INCIDENCE OF LISTERIA SPECIES FROM DAIRY ENVIRONMENTAL SAMPLES
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Date
2020-08
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KARNATAKA VETERINARY, ANIMAL AND FISHERIES SCIENCES UNIVERSITY, BIDAR
Abstract
In present study, Listeria count in soil, fodder, dung and feed samples collected
from university dairy farm ranged from 2.30 to 3.14 log10cfu/g. Udder swab, pail rinse, pail
milk and can milk had Listeria count of 0.30 log count while 0.60 log count observed in
chilled milk whereas water, swabs of hand, udder and equipment, pail and can rinses,
aseptic milk and pasteurized milk did not show the presence of Listeria. Among 23 isolates
of Listeria obtained from dairy environmental samples, Listeria monocytogenes
predominated (56.50) followed by Listeria innocua (17.39), Listeria ivanovii (8.70);
Listeria seeligeri (4.35) and 13.06 per cent of unidentified Listeria sp. All the 23 Listeria
isolates, except L. monocytogenes L16 grew well at 5 °C indicating psychrotrophic nature
of the isolates. At deep freeze temperature (-18 °C), only 9 out of 23 Listeria isolates
showed growth indicating the psychrophilic nature of isolates. Among 23 Listeria isolates,
14 numbers of Listeria spp. showed haemolysis, phospholipase and coagulase activities
indicating pathogenic nature. Listeria monocytogenes L10 showed highest DMC of 8.95
log10/ml among 23 isolates and used in further studies. Initial viable log count of Listeria
monocytogenes L10 in sterile milk 5.95 reached to 8.98 with per cents of 0.30 LA; protein
of 1.00, oleic acid of 1.86 and haemolysin of 10 mm diameter at 24 h of incubation at 37
°C. L. monocytognes L10 at 3, 4, 5 and 6 viable log counts inoculated into sterile whole
milk and stored at 5 °C the raise on an average viable log count was by 4, 3, 2 and 1.5 with
storage period of 30, 20, 12 and 9 days, respectively based on the curdling of milk. During
storage, the percent mean acidity of 0.23, protein reduction by 1.25, developed oleic acid
was 1.40. Haemolysin production in L. monocytognes L10 started on half of storage period
that reached peak on last day of storage at 5 °C