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COMPARATIVE ANALYSIS OF GROWTH KINETICS OF LISTERIA MONOCYTOGENES LINEAGES I AND II IN CHOPPED RED CABBAGE AND CUCUMBER USING PRIDICTIVE MODELING
Title
COMPARATIVE ANALYSIS OF GROWTH KINETICS OF LISTERIA MONOCYTOGENES LINEAGES I AND II IN CHOPPED RED CABBAGE AND CUCUMBER USING PRIDICTIVE MODELING
Creator
Qi, Yan
Date
2015, 2015-07
Description
Recently, outbreaks oflisteriosis assoc iated with cons umption of contaminated fresh produce by Listeria monocytogenes have increased....
Show moreRecently, outbreaks oflisteriosis assoc iated with cons umption of contaminated fresh produce by Listeria monocytogenes have increased. However, we know little about L. monocytogenes persistence and growth in fresh-cut produce items . The two main human foodbome outbreak lineages ofL. monocytogenes are LI and LB. Strains in LI (including serotypes 1/2b and 4b) are most likely to be isolated from human with listeriosis and Strains in LII (including serotypes 1/2a and 1/2c) are most likely to be isolated from food products and the natural environment. In order to determine the comparative survival and growth kinetics of these two lineages in chopped red cabbage and cucumber, samples of produce were chopped into 100 grams quantities and inoculated with 104 CFU/g of a cocktail of either LI (F2365, H7858, R2-502) or LII (LS814, JI-I 01, J1-067) antibiotic resistant strains. Samples were stored in deli-style containers at 5 or 10°C for 14 days, or 25°C for 7 days. At various intervals, samples were stomached and plated onto PCA with appropriate antibiotics. Data were modeled using DMFit from ComBase and statistical analyses were performed with GraphPad InStat. A p -value less than 0.05 was considered significant. The res ults for the grow th rates ((logIOCFU/g)/h) of the L. monocytogenes LI cocktail in red cabbage were significantly higher at 5°C (0.006±0.003), 10°C (0.017±0.004), and 25°C (0.051±0.017) than the LII cocktail ; and L. monocytogenes LI cocktail in cucumber were significantly lower at 25°C (0.098±0.00 84). Secondary models using the Ratkowsky equation presented r 2 values of 0.9866 for LI in red cabbage whereas presenting / values of 0.9998 and 0.9997 for LI and LII in cucumber, respectively. No significant difference between two lineages was seen in red cabbage and cucumber during ambient temperature display. Finally, the behavior of L. monocy togenes LI and LII on red cabbage and cucumber after potential consumer temperature abuse was determined. In red cabbage, LI grew steadily. However, the growth of L1I in red cabbage was more dynamic. In cucumber, there was no significant difference between LI and LII. The result s from this study will aid in comparing the growth and survival kinetics of Ll and L1l of L. monocytogenes and will provide guidance to both customers and the food industry.
M.S. in Food Safety and Technology, July 2015
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LISTERIA MONOCYTOGENES SURVIVAL AND GROWTH IN FLAVORED MILKSHAKES MADE FROM NATURALLY-AND ARTIFICIALLY-CONTAMINATED ICE CREAM
Title
LISTERIA MONOCYTOGENES SURVIVAL AND GROWTH IN FLAVORED MILKSHAKES MADE FROM NATURALLY-AND ARTIFICIALLY-CONTAMINATED ICE CREAM
Creator
Bathija, Vriddi Mahesh
Date
2016, 2016-12
Description
Listeria monocytogenes is the causative agent of the disease listeriosis and was implicated in a multistate foodborne outbreak associated with...
Show moreListeria monocytogenes is the causative agent of the disease listeriosis and was implicated in a multistate foodborne outbreak associated with ice cream spread over four years from 2010 to 2014 in Kansas, Oklahoma, Texas and Arizona. Ten illnesses were reported during the course of this outbreak, resulting in 100% hospitalization and a mortality rate of 33%; the individuals who died in the outbreak had consumed milkshakes made with the contaminated ice cream. The ice cream was found to be contaminated uniformly at 10 MPN/g. This study assessed the growth kinetics of L. monocytogenes in milkshakes made with naturally- and artificially-contaminated ice cream, and with or without flavoring agents. Artificial-contamination of ice cream samples included inoculation with a cocktail of rifampicin-resistant L. monocytogenes into the middle of the product using a wide-orifice pipet tip. Milkshake were prepared with or without strawberry, chocolate, or mint flavoring, using the recipe associated with the healthcare facility where the illnesses occurred. Milkshakes were stored in sterile plastic cups at 10ºC and an asymmetric (3 tubes of 100ml, 5 tubes of 10 ml, 8 tubes of 1ml and 8 tubes of 0.1ml sampling scheme) most probable number (MPN) enumeration was conducted after 0, 12, 24, 48, 72, 96 and 144 h. The Baranyi model was used to model L. monocytogenes growth rates, maximum populations, and lag phases. Compared to milkshakes made with no flavoring agents, the milkshakes with flavoring resulted in decreased growth rates for L. monocytogenes for both contamination states; the lowest growth rate of the pathogen was observed in strawberry flavored milkshakes made from artificially-contaminated ice cream (0.029 log CFU/ml per hour). Chocolate and mint flavorings resulted in significantly (P < 0.05) longer lag phases for both natural (68.2 and 83.0 h) and artificial-contamination (47.7 and 54.2 h, respectively). The highest maximum population (5.79 log CFU/ml) was achieved by L. monocytogenes in naturallycontaminated milkshakes without any flavoring agent. Since challenge studies often depend on the artificial contamination of a food product, this study evaluated the differences between artificial and natural contamination of L. monocytogenes in milkshakes. The data obtained can be used for risk assessment purposes.
M.S. in Food Safety and Technology, December 2016
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