Virulence Studies for Listeria spp. Recovered from Raw Ruminant Milk

Document Type : Original Article

Authors

Department of Microbiology, Faculty of Veterinary Medicine, Cairo University, Egypt

Abstract

In this study, 512 milk samples (103 raw cow’s milk, 100 raw buffaloes milk, 107 raw goats milk, 102 raw ewes milk and 100 raw she-camels milk). The incidence of Listeria among the different ruminant milk species was 6.1%. The isolated Listeria spp. were distributed as 9 isolates from cows, 8 isolates from buffaloes, 6 isolates from goats, 8 isolates from ewes and 4 isolates from she —camels raw milk. The Listeria spp. The Listeria spp. were distributed as 7 isolates of L. monocytogenes, 4 isolates L. innocua, 8 isolates L. welshimeri, 7 strains L. seelegeri and 5 isolates L. grayi in a percentage of 1.4%, 0.8%, 1.6%, 1.4% and 0.98% respectively. The results of virulence study revealed that all of the tested Listeria isolates were strong positive for Congo red after 24 hrs. Virulence of the Listeria isolates was also investigated by detection of hemolysis on blood agar, i/p injection to mice and intraocular distillation in rabbits. Hemolysis on blood agar, death of mice and eye inflammation in rabbits within 24h after injection in an incidence of 100% in case of L. monocytogenes isolates (virulent). On the other hand the suspected isolates of L. innocua, L. seelegeri, L. welshimeri and L. grayi showed negative results (a virulent). 

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Veterinary Medical Journal (Giza)
Volume 62, Issue 1
January 2016
Pages 15-19

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