A review of conventional detection and enumeration methods for pathogenic bacteria in food

Abstract

With continued development of novel molecular-based technologies for rapid, high-throughput detection of foodborne pathogenic bacteria, the future of conventional microbiological methods such as viable cell enumeration, selective isolation of bacteria on commercial media, and immunoassays seems tenuous. In fact, a number of unique approaches and variations on existing techniques are currently on the market or are being implemented that offer ease of use, reliability, and low cost compared with molecular tools. Approaches that enhance recovery of sublethally injured bacteria, differentiation among species using fluorogenics or chromogenics, dry plate culturing, differentiation among bacteria of interest using biochemical profiling, enumeration using impedence technology, techniques to confirm the presence of target pathogens using immunological methods, and bioluminescence applications for hygiene monitoring are summarized here and discussed in relation to their specific advantages or disadvantages when implemented in a food microbiology setting.

Development of an Improved Selective and Differential Medium for Isolation of Salmonella spp

“…(14,21,26,23,31). These media incorporate chromogenic substrates which are metabolized by Salmonella spp.…”

Salmonella Detection Methods for 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 TetrathionateNovobiocin 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.…”

Rapid Enumeration of Microbial Cells in Solubilized Soymilk Using an Automatic Cell Counting System with LED Illumination

“…Therefore, a simple, rapid, and accurate detection method is desirable. Several non-culture methods have been used for the rapid detection of bacteria in food (Fujikawa and Morozuki, 2003;Gracias and Mckillip, 2004;Kawasaki et al, 2004;Kawasaki et al, 2007;Masuda-Nishimura et al, 2000;Miyamoto et al, 1998). PCR is a useful technique because of its high sensitivity.…”