Salmonella Detection Methods for Food and Food Ingredients

Salmonella -A Dangerous Foodborne Pathogen 374 advances introduced for the improvement of conventional culture methods, the use of Polymerase Chain Reaction (PCR) technology, immunology-based methods, and bacteriophage based assays.Whenever possible, examples from the academic literature as well as from commercial applications will be considered.The importance of sample preparation will be examined throughout as it relates to its impact on sensitivity and turnaround time for detection.Specific Salmonella serovars will be named according to the nomenclature of Leminor and Popoff (2001), e.g.Salmonella Enteritidis or S. Enteritidis. Culture methodsCulture based methods are still the most widely used detection techniques and remain the gold standard for the detection of Salmonella due to their selectivity and sensitivity.For instance, the US Food and Drug Administration (FDA) and the Food Safety and Inspection Service (FSIS) of the US Department of Agriculture (USDA), requires an isolated organism as unambiguous proof of contamination (Alocilja and Radke 2003).Depending on the approach, standard culture methods typically require 5-7 days to obtain a result as they rely on the ability of Salmonella to multiply to visible colonies, which can then be characterized by performing additional biochemical and or serological tests.Due to their widespread use, numerous and varied bacteriological media (selective enrichment broths and selective agar plates) are applied to best monitor for Salmonella in food and food ingredients.The media may contain inhibitors in order to stop or delay the growth of non-target organisms, or particular substrates that only the target bacteria can degrade, or that confer a particular colour to the growing colonies (Manafi 2000).Cultural methods typically involve the enrichment of a portion of the food sample to recover sub-lethally injured cells due to heat, cold, acid, or osmotic shock (Sandel et al. 2003;Gracias and McKillip 2004) in a non-selective pre-enrichment media, such as Buffered Peptone Water (BPW), and to increase the number of target cells as these are generally not uniformly distributed in foods, typically occur in low numbers, and may be present in a mixed microbial population.Next, primary enrichment cultures are typically inoculated into secondary selective enrichment broths, such as Selenite Cystine broth (SC), Rappaport Vasiliadis Soy broth (RVS), Tetrathionate Broth (TT), or Muller-Kauffmann Tetrathionate-Novobiocin broth (MKTTn) and incubated at elevated temperatures (37 °C or 42°C for 18-24 hours) before being struck onto selective agars such as Xylose Lysine Deoxycholate agar (XLD agar), Bismuth Sulphite agar (BIS), Brilliant Green agar (BG) with or without the addition of sulfadiazine or sulfapyridine (BGS), modified semisolid Rappaport Vasiliadis (MSRV), Salmonella Shigella Agar, or Hektoen Enteric agar.There are several published standard methods utilizing combinations of media such as the current ISO horizontal method, ISO 6579:2002ISO 6579: (updated in 2007) ) for the detection Salmonella, including Salmonella Typhi and Salmonella Paratyphi applicable to products intended for human consumption and the feeding of animals, and to environmental samples in the area of food production and food handling.Similar standard methods have been published elsewhere, most notably in the FDA Bacteriological Analytical Manual (BAM).Typical Salmonella colonies based on morphology and or indicative biochemical reactions on selective agars are then cultured onto non-selective media prior to confirmatory testing.There are well-established confirmations and identification procedures for Salmonella.Preliminary identification is traditionally performed using classical biochemical and serological tests.Key biochemical tests include the fermentation of glucose, negative urease www.intechopen.

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