PHYLOGENETIC STUDY OF LISTERIA SPECIES ISOLATED FROM DAIRY ENVIRONMENTAL SAMPLES
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Date
2021-07-01
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KARNATAKA VETERINARY, ANIMAL AND FISHERIES SCIENCES UNIVERSITY, BIDAR – 585 401
Abstract
In the present study, Listeria count in dairy environmental samples collected from
university dairy farm ranged from 0.10 to 4.56 log10cfu/g, out of which soil, dung and
udder swab of milch animal showed more Listeria. The pheno and genotypic identity of
Listeria revealed as Listeria ivanovii (6 nos; 50.0%), followed by Listeria grayi (5 nos;
41.6 %) and Listeria seeligeri (1 no; 8.40%). Phylogenetic analysis through Neighbour
joining method revealed that L. ivanovii L18, L8, L16 and L. grayi L9, L10, L12 were
having relatedness about 87% while L. ivanovii L15, L7, L17, L. grayi L11, L13 and
Listeria seeligeri L14 had about 92% homology. Non-pathogenic Listeria grayi L13 and
pathogenic Listeria seeligeri L14 showed highest DMC of 8.69 and 8.20 log10/ml among
12 isolates and used in further studies. Initial 6 log viable count of Listeria grayi L13 and
Listeria seeligeri L14 in sterile skim milk reached to 8.00 and 8.58 log10cfu/ml with 0.64
and 0.62 %LA; protein of 1.00 and 1.62 respectively whereas L14 produced haemolysin of
9mm diameter at 24h of incubation at 37ºC. The viable cells of L13 and L14 were killed
when the contaminated milk was subjected to pasteurization, boiling and sterilization. L13
and L14 when inoculated at 6 log counts into sterile whole milk and stored at 5°C, the raise
in viable log count was 8.50 and 8.35 whereas titratable acidity reached to 0.19% and oleic
acid to 1.28 and 1.24% while protein content declined to 1.00 and 1.36% respectively with
storage period of 9 days.