Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 1/23/2009
Publication Date: 7/15/2009
Citation: Faith,N.,Kathariou,S.,Sahaghian,R.,Luchansky,J.,Czuprynski,C. 2009. Virulence for mice, resistance to synthetic gastric fluid, and biofilm formation of Listeria monocytogenes H7550, a serotype 4b strain isolated from frankfurters assocated with the BilMar listeriosis outbreak [abstract].Poster Presentation. IAFP Annual Meeting.Grapevine,TX.p.1. Interpretive Summary:
Technical Abstract: Introduction: One of the largest and most severe listeriosis outbreaks in the United States occurred in 1998 as a result of contamination of frankfurters with a serotype 4b strain of Listeria monocytogenes. However, there has been little characterization of the virulence attributes of strains retained from this outbreak. Purpose: We compared phenotypic and genotypic characteristics of L. monocytogenes strain H7550, a serotype 4b strain isolated from vacuum-packaged frankfurters, and a cadmium-sensitive plasmid pLM80-free derivative (H7550cds) of this strain. Methods: Virulence was assessed flowing intragastric (i.g.) inoculation of anesthetized A/J mice with approximately 106 CFU of each strain. We also separately compared their ability to invade and multiply within Caco-2 intestinal epithelial cells, their resistance to inactivation in synthetic gastric fluid (pH 4.5 at 37 degree C), and their ability to form biofilms on a plastic surface in vitro. A transposon mutant of strain H7550 that lacks adenylosuccinate lyase activity (strain J22F), and a non-hemolytic (LLO-) transposon mutant of strain H7550cds (J29H), were also included in our experiments. Results: Comparable numbers of CFU were recovered from the spleen, liver, blood, gallbladder, and ceca of mice inoculated with either strain H7550 or H7550cds, whereas mutants J22F and J29H of strain H7550cds were avirulent in our mouse model. More specifically, we did not recover viable cells from any of the internal organs except for low numbers of strain J22F from the ceca of a few mice. Experiments are underway to assess whether the mutant strains display a diminished ability to invade and multiply within Caco-2 cells. Likewise, we observed no significant differences in the resistance of stationary phase cells of the various strains to synthetic gastric fluid. We obtained preliminary evidence to suggest that mid-log phase cells of strain J22H are more resistant to inactivation at pH 4.5 than mid-log phase cells of the other strains examined. Strains H7550 and H7550cds both formed biofilms on plastic surfaces within 24 hr in vitro, with the latter strain being somewhat better than the former. Strain J22F was better able to form biofilms in vitro than its parent strain H7550, and mutant strain J29H was not significantly different from its parent strain H7550cds in biofilm formation. Significance: Strain H7550 and its cadmium sensitive derivative H7550cds are equally virulent for mice and equally resistant to synthetic gastric fluid, but may exhibit minor differences in their ability to form biofilms in vitro. Transposon mutant strains J22F and J29H were avirulent for mice. The former provides the first evidence that adenylosuccinate lyase activity is required for virulence in mice.