development-more-sensitive-specific-chromogenic-agar-medium-for

Development of a More Sensitive and Specific Chromogenic Agar Medium for the Detection of <em>Vibrio parahaemolyticus</em> and Other <em>Vibrio</em> Species

Foodborne infections in the US caused by Vibrio species have shown an upward trend. In the genus Vibrio, V. parahaemolyticus is responsible for the ...

California Polytechnic State University

Recognized to confer health benefits to consumers, probiotics such as Lactobacillus acidophilus are commonly incorporated into fermented dairy products worldwide; among which yogurt is a popular delivery vehicle. To materialize most of the putative health benefits associated with probiotics, an adequate amount of viable cells must be delivered at the time of consumption. However, the loss in their viabilities during refrigerated storage has been demonstrated previously. This study focused on the effects of yogurt starter cultures on the survival of five strains of L. acidophilus, with emphases on low pH and acid production. Differential survival behavior between L. acidophilus strains was further analyzed. To this end, viable cell counts of L. acidophilus were determined weekly during 4°C storage in various types of yogurts made with Streptococcus thermophilus alone, L. delbrueckii ssp. bulgaricus alone, both species of the starter cultures, or glucono-delta-lactone (GDL). All yogurt types, except for pasteurized yogurts, were co-fermented with L. acidophilus. Yogurt filtrate was analyzed for the presence of any inhibitory substance and for the amount of hydrogen peroxide. Multiplication of L. acidophilus was not affected by the starter cultures as all strains reached high level on day 0 of the storage period. Throughout the 28-day storage period, cell counts of L. acidophilus PIM703 and SBT2062 remained steady (~6 × 10(7)CFU/g) in yogurts made with both starter cultures, whereas those of ATCC 700396 and NCFM were reduced by a maximum of 3 and 4.6 logs, respectively. When starter cultures were replaced by GDL, all strains survived well, suggesting that a low pH was not a critical factor dictating their survival. In addition, the filtrate collected from yogurts made with starter cultures appeared to have higher inhibitory activities against L. acidophilus than that made with GDL. The presence of viable starter cultures was necessary to adversely affect the survival of some strains, as pasteurized yogurts had no effect on their survival. In particular, the inhibitory effect exerted by L. delbrueckii ssp. bulgaricus on L. acidophilus NCFM was highly pronounced than by S. thermophilus, nevertheless, the same effect was not observed on SBT2062. The inhibition against stationary-phase NCFM cells might be caused by the elevated level of hydrogen peroxide produced by L. delbrueckii ssp. bulgaricus. Delineating factors driving the differences in survival trait among probiotic strains will lead to a more efficacious delivery of health benefits in fermented dairy products through targeted technological interventions.

Effects of yogurt starter cultures on the survival of Lactobacillus acidophilus.

Enhancing the quality and safety of dairy food is critical to maintaining the competitiveness of dairy products in the food and beverage market and in reinforcing consumer confidence in the dairy industry. Raw milk quality has a significant effect on finished product quality. Several microbial groups found in raw milk have been shown to adversely affect the shelf life of pasteurized milk. Current microbiological criteria used to define milk quality are based primarily on culture-dependent methods, some of which are perceived to lack the desired sensitivity and specificity. To supplement traditional methods, culture-independent methods are increasingly being used to identify specific species or microbial groups, and to detect indicator genes or proteins in raw milk or dairy products. Some molecular subtyping techniques have been developed to track the transmission of microbes in dairy environments. The burgeoning "-omics" technologies offer new and exciting opportunities to enhance our understanding of food quality and safety in relation to microbes. Metagenomics has the potential to characterize microbial diversity, detect nonculturable microbes, and identify unique sequences or other factors associated with dairy product quality and safety. In this review, fluid milk will be used as the primary example to examine the adequacy and validity of conventional methods, the current trend of culture-independent methods, and the potential applications of metagenomics in dairy food research.

ADSA Foundation Scholar Award: Trends in culture-independent methods for assessing dairy food quality and safety: emerging metagenomic tools.

Foodborne diseases represent a significant public health burden to the United States, considering that they cause illness in 1 in 6 people annually, which amounts to ∼48 million people (E. Scallan, R. M. Hoekstra, F. J. Angulo, R. V. Tauxe, M. A. Widdowson, S. L. Roy, J. L. Jones, and P. M. Griffin, Emerg Infect Dis 17:7-15, 2011). The average national cost of illness associated with 30 foodborne pathogens is estimated to be $55.5 to $93.2 billion based on two cost-of-illness models (R.L. Scharff, J Food Prot 78:1064-1071, 2015). Predominately, foodborne illnesses are the result of accidental contamination or unintentional mishandling of food materials during the farm-to-table continuum. Nevertheless, principles and methodologies derived from microbial forensics are applied in foodborne outbreaks investigation to determine the source of the pathogen. Drawing from multiple real-life examples and case studies, this review discusses how the current food industry practice, demography, and consumer preference are shaping the landscape of food safety. The approaches to source tracking, or traceback, are described, with a focus on bacterial pathogens associated with food-producing animals. Current challenges and opportunities in microbial forensics in food safety are also addressed.

Article	Year
Effects of yogurt starter cultures on the survival of Lactobacillus acidophilus. International journal of food microbiology\| PubMed ID: 21196060	2011
ADSA Foundation Scholar Award: Trends in culture-independent methods for assessing dairy food quality and safety: emerging metagenomic tools. Journal of dairy science\| PubMed ID: 23040017	2012
Microbial Forensics in Food Safety. Microbiology spectrum\| PubMed ID: 27726773	2016

Marie Yeung

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