INTRAGASTRIC INOCULATION WITH A COCKTAIL OF LISTERIA MONOCYTOGENES STRAINS DOES NOT POTENTIATE THE SEVERITY OF INFECTION IN A/J MICE COMPARED TO INOCULATION WITH THE INDIVIDUAL STRAINS COMPRISING THE COCKTAIL

Authors: FAITH, NANCY - UNIVERSITY OF WISCONSIN; PETERSON, LUKE - UNIVERSITY OF WISCONSIN; Luchansky, John; CZUPRYNSKI, CHARLES - UNIVERSITY OF WISCONSIN

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2006
Publication Date: 11/1/2006
Citation: Faith, N.G., Peterson, L.D., Luchansky, J.B., Czuprynski, C.J. 2006. Intragastric inoculation with a cocktail of listeria monocytogenes strains does not potentiate the severity of infection in a/j mice compared to inoculation with the individual strains comprising the cocktail. Journal of Food Protection. 69(11):2664-2670.

Interpretive Summary: Listeriosis is an important food borne disease both in the United States and throughout the world. To better understand the pathogenesis of Listeria monocytogenes it is important to develop suitable animal models for studying listeriosis and in particular to select appropriate strains to conduct such studies. Whereas food inoculation studies often use a cocktail of 4 to 6 strains, animal feeding trials typically inoculate animals with a single strain of this pathogen. The underlying rationale is that by using several strains that may vary somewhat from each other in key traits, one gains a better understanding of the persistence of such strains in the food supply and/or their pathogenicity in a human or animal host. As such, the purpose of this study was to assess a 5-strain cocktail of L. monocytogenes, similar to that previously reported for assessing viability of this pathogen in foods, for its virulence in a mouse model of listeriosis. We could find no such studies that directly compare the in vivo virulence of a multi-strain cocktail of L. monocytogenes with that of the respective individual strains. Our findings established that intragastric inoculation of mice with combinations of strains of L. moncytogenes, grown under standard conditions in microbiological broth, offers no advantage over separate inoculation with each of the individual strains of the cocktail relative to their lethality assessment.

Technical Abstract: Although multi-strain cocktails of Listeria monocytogenes are used in food inoculation experiments, no studies have been reported using these cocktails in an intragastric mouse model. In this study we used a five-strain L. monocytogenes cocktail consisting of strains ScottA, MFS108, 101M, V7, and 310, and a four-strain listeriae cocktail containing strains ScottA, EGD, H7738, and F2365. Herein we report that intragastric inoculation of mice with ca. 10**6 CFU of a cocktail of L. monocytogenes strains does not result (P>0.05) in a more severe infection (based on CFU of listeriae recovered from the spleen, liver and blood) than inoculation of mice with similar numbers of the individual strains comprising the cocktail. Nor did we observe any correlation between susceptibility of these strains to inactivation in synthetic gastric fluid in vitro when used alone or in combination. Based on the low recovery of some environmental strains from tissues of inoculated mice, it is recommended that future efforts to address the pathogenesis of gastrointestinal listeriosis use a combination of strains either proven to be virulent in vivo or associated with human food borne disease outbreaks.