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Natural Atypical Listeria Innocua Strains With Listeria Monocytogenes Pathogenicity Island 1 Genes

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Abstract:The detection of the human foodborne pathogen, Listeria monocytogenes, in food, environmental samples and clinical specimens associated with cases of listeriosis, a rare but high mortality-rate disease, requires distinguishing the pathogen from other Listeria species. Speciation of bona fide Listeria isolates into the six species of the genus is normally a relatively simple few-test process. Occasionally aberrant isolates are found but even then their speciation is usually possible with only one or two extra confirmatory tests. We have discovered a hemolytic, rhamnose- and xylose-fermentation negative Listeria strain with surprising recalicitrance to speciation. The L. monocytogenes-negative results with two L. monocytogenes confirmatory tests, for which no false negatives have been reported to date, were contradicted by the L. monocytogenes -positive result of another confirmatory test for L. monocytogenes genes for which no false posititves results have been reported to date. The issue had to be resolved by using total DNA/DNA hybridization testing and then confirmed by further specific PCR tests made possible by the recently published gene sequences of L. monocytogenes and L. innocua. The results show that this isolate is indeed a novel one. It provides the first fully documented instance of the discovery of a hemolytic Listeria innocua strain. This species is typically non-hemolytic. The L. innocua isolate contains at least an overall representation, if not a facisimile, of the PrfA regulated virulance gnee cluster of L. monocytogenes. It apparently does not contain all the extra-cluster virulence genes because it is avirulent in the mouse pathogenicity test. At least one of these extra cluster virulence genes, the L. monocytogenes-specific allele of iap, which is not PrfA regulated, is not fully present, if at all. The virulence gene cluster contains hyl, the gene, which codes for the hemolysin (listeriolysin O) of the L. monocytogenes. In addition to the hemolysin at least one of the other genes of the cluster, plcA, is expressed in this strain of L. innocua. The detection of specific L. innocua genes in the strain is consistent with its L. innocua DNA/DNA hybridization identity. Further study of this strain may contribute to our understanding of evolution, particularly of virulence, in the genus Listeria.
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Citation:Johnson, J., J. Jinneman, G. N. Stelma Jr., B. G. Smith, D. Lye, J. W. Messer, J. Ulaszek, L. Evsen, S. Gendel, R. W. Bennett, B. Swaminathan, J. Pruckle, A. Steigerwalt, S. Kathariou, S. Yildirim, D. Volokhov, A. Rasooly, V. Chizhikov, M. Wiedmann, E. Fortes, R. E. Duvall, and A. D. Hitchins. Natural Atypical Listeria Innocua Strains With Listeria Monocytogenes Pathogenicity Island 1 Genes. APPLIED AND ENVIRONMENTAL MICROBIOLOGY 70(7):4256-4266, (2004).
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Contact: Mary P. O'Bryant - (919)-541-4871 or obriant.mary@epa.gov
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Division: Microbiological & Chemical Exposure Assessment Division
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Branch: Microbial Exposure Research Branch
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Product Type: Journal
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Published: 07/01/2004
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