Salmonella Detection Methods for Food and Food Ingredients

Salmonella is the etiologic agent of Salmonellosis in humans causing severe illness in infants, the elderly, and immunocompromised patients (Cross et al. 1989; Tauxe 1991; Smith 1994; Baumler et al. 2000). Salmonellosis symptoms include watery diarrhea, abdominal pain, nausea, fever, headache and occasional constipation with hospitalization required in cases of severe infections. The genus currently contains two species, Salmonella bongori and Salmonella enterica (including six subspecies: enterica (I), salamae (II), arizonae (IIIa), diarizonae (IIIb), houtenae (IV), and indica (VI). However, there are more than 2,500 serovars of Salmonella based on the Kauffmann-White antigenic scheme for the classification of Salmonellae (Popoff et al. 1994). Salmonella is a gram-negative, non-spore forming rod and facultative anaerobe that can ferment glucose belonging to the family Enterobacteriaceae. Most strains are motile with peritrichous flagella and can reduce nitrate to nitrite (Grimont et al. 2000). The organism is mesophilic with optimum growth temperature in the range of 32 – 37°C but capable of growth within a wide temperature range of 6 – 46oC. Salmonella is ubiquitous in the environment originating from the gastrointestinal tracts of domesticated and wild animals and can be present without causing apparent illness. Most infections result from the ingestion of foods of animal origin contaminated with Salmonella species such as beef, chicken, turkey, pork, eggs, and milk (D’Aoust 1997; D’Aoust 2000; Olsen et al. 2000). Other vehicles, including non-animal foods such as fresh fruits and vegetables (Mahon et al. 1997), reptiles (Friedman et al. 1998), water (Angulo et al. 1997), and direct person-to-person transmission (Lyons et al. 1980), have also been implicated. However, certain serotypes of Salmonella such as S. Enteritidis, which can penetrate poultry reproductive organs resulting in the contamination of egg contents has been a prominent cause of human illness for several decades (Gantois et al. 2009). In addition to faecal contamination, cross-contamination of foods by Salmonella during food preparation can be an important source of foodborne illness. Generally, detection methods are based on physiological and biochemical markers of the organism (Williams 1981). Cultural methods are based on nutrient acquisition, biochemical characteristics, and metabolic products unique to Salmonella spp. (Ricke et al. 1998). More rapid immunological and molecular screening methods of detection have been devised to detect cell surface markers and nucleic acids, respectively. This chapter will provide an overview of various culture based methods and rapid methods currently available for the detection of Salmonella in foods and food ingredients. We will focus our discussion on