Evaluation of BBL CHROMagar Listeria agar for the isolation and identification of Listeria monocytogenes from food and environmental samples Veena Hegde a , Carlos G. Leon-Velarde a , Christina M. Stam b , Lee-Ann Jaykus b , Joseph A. Odumeru a, ⁎ a Laboratory Services Division, University of Guelph, 95 stone Rd. West, Guelph, ON, Canada N1H 8J7 b Food Science Department, North Carolina State University, Raleigh, NC 27695-7624, USA Received 21 June 2006; received in revised form 22 June 2006; accepted 22 June 2006 Available online 23 August 2006 Abstract The performance of BBL CHROMagar Listeria chromogenic agar for the detection of Listeria monocytogenes was evaluated for its ability to isolate and identify L. monocytogenes from food and environmental samples. The medium was compared to non-chromogenic selective agars commonly used for Listeria isolation: Oxford, Modified Oxford, and PALCAM. BBL CHROMagar Listeria had a sensitivity of 99% and 100% for the detection of L. monocytogenes from 200 natural and artificially inoculated food samples, respectively, with a colony confirmation rate of 100%. The sensitivity of non-chromogenic selective media for the detection of L. monocytogenes from these same samples was 97–99% with colony confirmation rates of 65–67.5%. From 93 environmental samples, BBL CHROMagar Listeria agar results correlated 100% with a Listeria spp. visual immunoassay (TECRA) performed on these same samples and the USDA–FSIS standard culture method for the isolation of L. monocytogenes. From environmental samples, the L. monocytogenes confirmation rate was 100% for BBL CHROMagar Listeria as compared to 50% for conventional agars tested. On BBL CHROMagar Listeria, L. monocytogenes forms a translucent white precipitation zone (halo) surrounding blue-pigmented colonies of 2–3 mm in diameter, with an entire border. BBL CHROMagar Listeria offers a high degree of specificity for the confirmation of suspect L. monocytogenes colonies, whereas non-chromogenic selective agars evaluated were not differential for L. monocytogenes from other Listeria species. © 2006 Elsevier B.V. All rights reserved. Keywords: Listeria monocytogenes; Listeria species; Chromogenic agar 1. Introduction Of the six species of Listeria, Listeria monocytogenes is pathogenic to humans causing listeriosis, a rare cause of foodborne disease with fewer than four cases per million individuals per year reported in developed countries, yet causing a severe human infection with an overall 20–30% mortality rate among hospitalized patients (Dussurget et al., 2004; Reissbrodt, 2004). Clinical features include severe gastroenteritis, mother-to-child infections, and central nervous system infections, with the young, elderly, and the immuno- compromised being the most susceptible (Mead et al., 1999). L. monocytogenes foodborne infection is primarily asso- ciated with the consumption of contaminated minimally processed foods, particularly refrigerated ready to eat foods where modified atmosphere packaging is used to extend the shelf life of the product (McLauchlin, 1996; Low and Donachie, 1997; Schlech, 2000). Various studies have indicated that certain strains of L. monocytogenes survive well within the food-processing environment (Nørrung and Skovgaard, 1993; Fenlon, 1996; Unnerstad et al., 1996; Senczek et al., 2000) and the persistence of such strains is of concern as they have the potential to act as a continual source of contamination (Sashara and Zottola, 1993). Journal of Microbiological Methods 68 (2007) 82 – 87 www.elsevier.com/locate/jmicmeth ⁎ Corresponding author. Fax: +1 519 767 6240. E-mail address: jodumeru@lsd.uoguelph.ca (J.A. Odumeru). 0167-7012/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.mimet.2006.06.011