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Applied and Environmental Microbiology, September 2007, p. 5401-5410, Vol. 73, No. 17
0099-2240/07/$08.00+0     doi:10.1128/AEM.00354-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Distribution and Characteristics of Listeria monocytogenes Isolates from Surface Waters of the South Nation River Watershed, Ontario, Canada

Agriculture and Agri-Food Canada, London, Ontario, Canada N5V 4T3,¹ INRA—Université de Bourgogne, UMR 1229, Microbiologie du Sol et de l'Environnement, CMSE BP 86510, F-21065 Dijon, France,² Agriculture and Agri-Food Canada, Ottawa, Ontario, Canada K1A 0C6,³ Bureau of Microbial Hazards, Health Canada, Ottawa, Ontario, Canada K1A 0L2,⁴ INRA—Université de Bourgogne, UMR 1232, Laboratoire de Microbiologie, F-21065 Dijon, France,⁵ Health Canada, Ottawa, Ontario, Canada K1A 0K9,⁶ Environment Canada, Burlington, Ontario, Canada L7R 4A6,⁷ Public Health Agency of Canada, Lethbridge, Alberta, Canada T1J 3Z4⁸

Received 13 February 2007/ Accepted 22 June 2007

Listeria monocytogenes is a facultative intracellular pathogen thought to be widely distributed in the environment. We investigated the prevalence and characteristics of L. monocytogenes isolates from surface waters derived from catchments within the South Nation River watershed (Ontario, Canada). This watershed is dominated by urban and rural development, livestock and crop production, and wildlife habitats. From June to November 2005, a total of 314 surface water samples were collected biweekly from 22 discrete sampling sites characterized by various upstream land uses. Presumptive Listeria spp. were isolated using a selective enrichment and isolation procedure, and 75 L. monocytogenes isolates were identified based on colony morphology, hemolytic activity, and amplification of three pathogenicity genes: iap, inlA, and hlyA. Thirty-two of 314 (10%) surface water samples were positive for the presence of L. monocytogenes, but detection ranged between 0 and 27% depending on the sampling date. Isolates belonging to serovar group 1/2a, 3a (50%) and group 4b, 4d, 4e (32%) were dominant. L. monocytogenes populations were resolved into 13 EcoRI ribotypes and 21 ApaI and 21 AscI pulsotypes. These had Simpson indexes of discrimination of up to 0.885. Lineage I-related isolates were dominant (61%) during the summer, whereas lineage II isolates were dominant (77%) in the fall. Isolates were, on average, resistant to 6.1 ± 2.1 antibiotics out of 17 tested. Half of the L. monocytogenes isolates exhibited potential virulence linked to the production of a functional internalin A, and some isolates were found to be moderately to highly virulent by in vitro Caco-2 plaque formation assay (up to 28% of entry). There was a statistically significant link between the occurrence of L. monocytogenes and proximity to an upstream dairy farm and degree of cropped land. Our data indicate that L. monocytogenes is widespread in the studied catchments, where it could represent a public health issue related to agricultural land use.

Published ahead of print on 13 July 2007.