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Applied and Environmental Microbiology, July 2004, p. 4256-4266, Vol. 70, No. 7
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.7.4256-4266.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Natural Atypical Listeria innocua Strains with Listeria monocytogenes Pathogenicity Island 1 Genes

J. Johnson,¹ K. Jinneman,¹ G. Stelma,² B. G. Smith,² D. Lye,² J. Messer,² J. Ulaszek,³ L. Evsen,⁴ S. Gendel,⁵ R. W. Bennett,⁵ B. Swaminathan,⁶ J. Pruckler,⁶ A. Steigerwalt,⁶ S. Kathariou,⁷ S. Yildirim,⁷ D. Volokhov,⁸ A. Rasooly,⁵ V. Chizhikov,⁸ M. Wiedmann,⁹ E. Fortes,⁹ R. E. Duvall,⁵ and A. D. Hitchins^5*

Food and Drug Administration, Bothell, Washington 98021,¹ Environmental Protection Agency, Cincinnati, Ohio 45268,² National Center for Food Safety and Technology, Summit-Argo, Illinois 60501,³ University of Maryland, College Park, Maryland 20742,⁴ Center for Food Safety and Applied Nutrition, Food and Drug Administration, College Park, Maryland 20740,⁵ Centers for Disease Control and Prevention, Atlanta, Georgia 30333,⁶ North Carolina State University, Raleigh, North Carolina 27695,⁷ Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, Maryland 20895,⁸ Cornell University, Ithaca, New York 14853⁹

Received 11 September 2003/ Accepted 5 April 2004

Identification of bona fide Listeria isolates into the six species of the genus normally requires only a few tests. Aberrant isolates do occur, but even then only one or two extra confirmatory tests are generally needed for identification to species level. We have discovered a hemolytic-positive, rhamnose and xylose fermentation-negative Listeria strain with surprising recalcitrance to identification to the species level due to contradictory results in standard confirmatory tests. The issue had to be resolved by using total DNA-DNA hybridization testing and then confirmed by further specific PCR-based tests including a Listeria microarray assay. The results show that this isolate is indeed a novel one. Its discovery provides the first fully documented instance of a hemolytic Listeria innocua strain. This species, by definition, is typically nonhemolytic. The L. innocua isolate contains all the members of the PrfA-regulated virulence gene cluster (Listeria pathogenicity island 1) of L. monocytogenes. It is avirulent in the mouse pathogenicity test. Avirulence is likely at least partly due to the absence of the L. monocytogenes-specific allele of iap, as well as the absence of inlA, inlB, inlC, and daaA. At least two of the virulence cluster genes, hly and plcA, which encode the L. monocytogenes hemolysin (listeriolysin O) and inositol-specific phospholipase C, respectively, are phenotypically expressed in this L. innocua strain. The detection by PCR assays of specific L. innocua genes (lin0198, lin0372, lin0419, lin0558, lin1068, lin1073, lin1074, lin2454, and lin2693) and noncoding intergenic regions (lin0454-lin0455 and nadA-lin2134) in the strain is consistent with its L. innocua DNA-DNA hybridization identity. Additional distinctly different hemolytic L. innocua strains were also studied.

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* Corresponding author. Mailing address: FDA, 5100 Paint Branch Pkwy., College Park, MD 20740. Phone: (301) 436-1649. Fax: (301) 436-2644. E-mail: Anthony.Hitchins{at}cfsan.fda.gov.

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Applied and Environmental Microbiology, July 2004, p. 4256-4266, Vol. 70, No. 7
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.7.4256-4266.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

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