Short communication Failure of foodborne pathogens to develop resistance to sanitizers following repeated exposure to common sanitizers Shadi Riazi, Karl R. Matthews * Food Science Department, School of Environmental and Biological Sciences, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901, USA article info Article history: Received 20 October 2010 Received in revised form 30 November 2010 Accepted 1 December 2010 Available online 28 December 2010 Keywords: Foodborne pathogens Antimicrobial resistance Resistance Sanitizers Salmonella Escherichia coli O157:H7 abstract The increased focus on food safety hygiene in the home and the food industry has resulted in an increasing use of chemical sanitizers. Whether the increased use of sanitizers will result in emergence of sanitizer-resistant foodborne pathogens has been speculated. Sanitizers that may be used in the home for sanitizing of surfaces or in hand sanitizers were evaluated and included sodium hypochlorite, chlo- rhexidine digluconate, and benzalkonium chloride. The adaptation of surface-associated and planktonic Escherichia coli O157:H7, Salmonella enterica subsp. enterica serovar Enteritidis, Staphylococcus aureus, Listeria monocytogenes and Pseudomonas aeruginosa to those sanitizers was investigated. In the suspension test, all sanitizers effectively reduced microbial number >5 log units after an exposure of 5 min. In the surface test, generally <3 log unit reduction was achieved when sanitizers were tested at 256 ppm. Repeated exposure of surface-associated bacteria resulted in a significant decrease in log number of cells after the first and second exposure to the sanitizer. Serial subculture of S. Enteritidis in sublethal concentrations of chlorexidine digluconate resulted in a stable decreased susceptibility to the agent, but not resistance. Results of this study suggest that foodborne bacterial pathogens remain susceptible to the sanitizers tested under conditions evaluated in this study. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Sanitizing food contact surfaces is an essential task in the home and in food processing plants since pathogens and food spoilage bacteria are spread to food contact surfaces during preparation of raw products, potentially creating food safety issues (Kusumaningrum et al., 2003a,b). The use of hand sanitizers is also prudent to limit or prevent the spread of bacteria from hands to food, utensils, equipment, and throughout the kitchen or process- ing facility. The incidence and persistence of foodborne pathogens in home kitchens has been established (Gorman et al., 2002). Different groups of chemical sanitizers are used by the food industry, or for that matter in the home, for neutralizing bacteria associated with food contact surfaces and individuals hands (Gronholm et al., 1999). The effectiveness of sanitizers against planktonic (suspended) cells is generally greater than against cells in a biofilm (attached cells) (Somers et al., 1994; Gibson et al., 1995). Bacterial cells that have attached to inert surfaces and are exposed periodically to a sanitizing agent may develop decreased sensitivity or resistance to that agent (Langsrud et al., 2003a,b). Moreover, research suggests that exposure to an antimicrobial agent can result in co-resistance or cross-resistance to other antimicrobial agents (Potenski et al., 2003; Golding and Matthews, 2004). The wealth of sanitizing products available for use in the home and industry is staggering. The present study focuses on three sanitizers: sodium hypochlorite, benzalkonium chloride, and chlorhexidine digluconate. These sanitizers exhibit activity against a wide range of Gram-positive and Gram-negative bacteria. Sodium hypochlorite is one of the most common sanitizers used by the food industry. In the home, a dilute solution (ca. 200e250 ppm sodium hypochlorite) of bleach may be used to sanitize cutting boards, counters, or the kitchen sink. Benzalkonium chloride is one of many quaternary ammonium compounds. The biocide is typically used for sanitizing work surfaces, but is found in a range of products from eye drops to hand sanitizers. Many topical sanitizers from hand wipes to teat dips for dairy cattle contain chlorhexidine digluconate. Chlorhexidine digluconate is also found in a range of personal care products. An unintended consequence of the use of these sanitizers may be development of resistant bacteria through adaptive and cross-adaptive responses. Bacteria can develop decreased susceptibility or even resistance to an antimicrobial agent following intermittent or continuous exposure to sublethal concentrations of a given antimicrobial agent (To et al., 2002). The methods employed by the microbe to survive * Corresponding author. Tel.: þ1 732 932 9611; fax: þ1 732 932 6776. E-mail address: Matthews@aesop.rutgers.edu (K.R. Matthews). Contents lists available at ScienceDirect International Biodeterioration & Biodegradation journal homepage: www.elsevier.com/locate/ibiod 0964-8305/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.ibiod.2010.12.001 International Biodeterioration & Biodegradation 65 (2011) 374e378