1.1 Background of Study
Food safety and quality is a global topic of public concern. Salmonella is a Gram negative bacteria, rod shaped, aerobic or facultative anaerobic, belonging to the Family Enterobacteriaceae and it is a major pathogenic bacterium,’inhabiting the intestinal tract of humans and animals (Holt et al.,1994). Salmonella spp are important causes of bacterial contamination of the environment and the food chain (Ponce et al., 2008), and are the leading causes of acute gastroenteritis in several countries.In developing countries, contaminated vegetables, water and human-to-human transmission are believed to contribute to comparatively larger proportion of human cases than those in industrialized countries (Acha and Szyfres, 2003; Soltan et al., 2009). Salmonellosis due to Salmonella spp is the most common food-borne disease in both developing and developed countries, although incidence rates vary according to human and animals (Gerosa and Skoet, 2013).
According to the Centers for Disease Control and Prevention (CDC, 2011); the genus Salmonella contains two species, Salmonella enterica and Salmonella bongori. S. enterica consists of six subspecies (Popoff and Le Minor, 2001) namely; S. enterica subsp enterica, S. enterica subsp salamae, S. enterica subsp arizonae, S. enterica subsp diarizonae, S. enterica subsp houtenae, S. enterica subsp indica. A relatively small number of these serotypes have been documented to be host specific, characteristically producing systemic disease in a restricted number of animal species. These serotypes include: S. Gallinarium and S. Pullorumin chickens; S. Dublinin cattle; S. Cholera-suisprimarily in pigs (Zhang-Barber et al., 1999).
Milk is often described as fresh, clean and normal mammary secretion obtained by milking of one or more dairy animals that are properly fed and kept or also defined as the fluid secreted by mammals for the nourishment of their young (Rani and Mahesh, 2012). In dairy animals, cow milk is the most consumed milk world-wide and in 2011, Food and Agricultural Organisation (FAO) estimated 85% of all milk world-wide was produced from cows (Gerosa and Skoet, 2013). The cow milk is a good source of animal proteins, fats, vitamins and minerals to the human body (Rani and Mahesh, 2012). Nutritionally less useful substances like enzymes are also present in normal cow milk, and some of these enzymes are used as indices in screening or quality control tests for fresh milk (Anonymous,2012). The principal components of milk are water, fats, proteins and lactose. High water activity, moderate pH (6.4-6.6) and ample nutrients make milk an excellent culture medium for microbial growth at suitable temperature (Adams and Moss, 2008).