Influence of Listeria innocua on the attachment of Listeria monocytogenes to stainless steel and aluminum surfaces Ok Kyung Koo 1 , Jean Baptiste Ndahetuye, Corliss A. O’Bryan, Steven C. Ricke, Philip G. Crandall * Center for Food Safety, Department of Food Science, University of Arkansas, Fayetteville, AR 72704, USA article info Article history: Received 1 August 2013 Received in revised form 29 October 2013 Accepted 5 November 2013 Keywords: Listeria monocytogenes Listeria innocua Attachment Food safety abstract Listeria monocytogenes is an important foodborne pathogen that may be transmitted from the food- processing environment to food; however, the ecology and interaction of this organism with microbial residents on surfaces within the food industry is not well understood. The current study was undertaken to investigate the influence of Listeria innocua on the growth and attachment of L. monocytogenes to stainless steel or aluminum surfaces at 23  C. When grown in broth as a mixed culture, L. innocua reached a higher cell count at 24 h than did L. monocytogenes. Attachment was evaluated by placing an aliquot containing 10 3 CFU/ml of L. innocua and 10 3 CFU/ml of L. monocytogenes on the coupons and by quan- tifying attached cells after 24 and 72 h. Attachment of L. monocytogenes was decreased by the presence of L. innocua. When compared to L. monocytogenes alone, there was a significant reduction of attachment of L. monocytogenes at 24 and 72 h on stainless steel and 72 h on aluminum surface when L. innocua was added at the same time. L. innocua exhibited an effect on the attachment of L. monocytogenes, increasing our knowledge of the behavior of L. monocytogenes in the presence of another Listeria species. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Listeria monocytogenes is an important foodborne pathogen that causes high hospitalization rates and high mortality (Gandhi & Chikindas, 2007). It has been difficult to completely eliminate this pathogen from the food-processing premises because the organism is widely distributed in nature and can survive under extreme conditions of temperature, pH and salts (Cole, Jones, & Holyoak, 1990; Gray & Killinger, 1966). Additionally, L. monocytogenes is able to attach and form biofilms on materials found in the food- processing environment, and cells in biofilms develop resistance to cleaning and disinfection (Beresford, Andrew, & Shama, 2001; Blackman & Frank, 1996; Somers & Wong, 2004). L. monocytogenes occurring in niches within processing facilities may cause contamination of food products (Lin et al., 2006; Wilks, Michels, & Keevil, 2006). Despite listeriosis outbreaks linking L. monocytogenes from the food-processing environment (CDC, 2011), investigation of the ecology of the pathogen and its interaction with other microbiota is not well understood (Hoelzer et al., 2011). Interaction of microorganisms attached on surfaces may inter- fere with or promote L. monocytogenes biofilm formation and development. Norwood and Gilmour (2001) observed a decrease of L. monocytogenes cell numbers attached to stainless steel coupons at 4  C, 18  C, and 30  C in the presence of Staphylococcus xylosus and Pseudomonas fragi. The decrease was attributed to the competition for nutrients and production of antagonistic com- pounds by S. xylosus. However, a separate study conducted by Sashara and Zottola (1993) demonstrated that the attachment of L. monocytogenes in the mixed-cultures was enhanced by the exo- polymer produced by P. fragi compared to the L. monocytogenes in pure culture. The non-pathogenic Listeria innocua is also abundant in the environment and has been isolated in the same niches as L. monocytogenes such as ground water and surface water samples, in fecal samples, or from the soil (Luppi, Bucci, Maini, & Rocourt, 1988; Weis & Seeliger, 1975; Welshimer, 1968). Several surveys of food production environments have reported a higher incidence and prevalence of L. innocua over L. monocytogenes (Aguado, Vitas, & Garcia-Jalon, 2004; Cox et al., 1989; Thimothe, Nightingale, Gall, Scott, & Wiedmann, 2004). Some researchers suggest that greater recovery of L. innocua may be due to more efficient utilization of * Corresponding author. Food Science, University of Arkansas, 2650 Young Ave., Fayetteville, AR 72704, USA. Tel.: þ1 479 575 5328; fax: þ1 479 5756936. E-mail address: crandal@uark.edu (P.G. Crandall). 1 Current address: Food Safety Research Group, Korea Food Research Institute, Seongnam-si, Gyeonggi-do, Republic of Korea. Contents lists available at ScienceDirect Food Control journal homepage: www.elsevier.com/locate/foodcont 0956-7135/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodcont.2013.11.008 Food Control 39 (2014) 135e138