ORIGINAL ARTICLE Inactivation of Escherichia coli O157:H7 and Salmonella on artificially or naturally contaminated mung beans (Vigna radiata L) using a stabilized oxychloro-based sanitizer R. Hora 1 , M. Kumar 1 , M. Kostrzynska 2 M. A. Dixon 3 and K. Warriner 1 1 Department of Food Science, University of Guelph, Guelph, ON, Canada 2 Agriculture & Agri-Food Canada, Guelph, ON, Canada 3 Environmental Biology, University of Guelph, Guelph, ON, Canada Introduction Over the last decade there has been numerous food-borne illness outbreaks linked to sprouted seeds such as alfalfa and bean sprouts (Fett et al. 2005). Salmonella is the most frequently encountered human pathogen on sprouts although cases involving Escherichia coli O157:H7 have also been reported (Mohle-Boetani et al. 2001; Fett et al. 2005). In the majority of outbreaks the seed used for sprout production has been shown to be the source of human pathogens (Anonymous 1999). Therefore, it was recommended that seeds should be treated with 20 000 ppm calcium hypochlorite prior to soaking and subsequently sprouting (Anonymous 1999). However, it is widely acknowledged that treatments based on hypo- chlorite or alternative sanitizing agents (e.g. peroxyacetic acid, hydrogen peroxide) can only reduce pathogen levels on seeds but cannot ensure complete elimination (Anony- mous 1999; Wessinger and Beuchat 2000; Brooks et al. 2001). This is relevant considering that even relatively low levels of surviving pathogens (<0Æ1 CFU g )1 ) can grow to densities in excess of 6 log CFU g )1 within 48 h into the sprouting process (Holliday et al. 2001). A successful decontamination method has been devised based on supplementing the soak water used in the early stages of sprout production with a stabilized oxychloro- based sanitizer (SOC) (Kumar et al. 2006). A previous study has demonstrated that SOC applied at 200 ppm for >19 h can consistently inactivate either E. coli O157:H7 or Salmonella introduced onto mung beans (Kumar et al. 2006). However, the efficacy of SOC to decontaminate naturally contaminated or damaged seed has yet to be Keywords Escherichia coli O157:H7, mung bean sprouts, Salmonella, seed decontamination, sodium chlorite. Correspondence Keith Warriner, Department of Food Science, University of Guelph, Guelph, ON, N1G 2W1, Canada. E-mail: kwarrine@uoguelph.ca 2006/0707: received 18 May 2006, revised 6 August 2006 and accepted 19 September 2006 doi:10.1111/j.1472-765X.2006.02049.x Abstract Aims: To evaluate the efficacy of a stabilized oxychloro-based (SOC) sanitizer to decontaminate mung beans artificially or naturally contaminated with Escherichia coli O157:H7 or Salmonella. Methods and Results: Naturally contaminated beans were produced by intro- ducing a five-strain cocktail of E. coli O157:H7 or Salmonella onto the flowers of growing mung bean plants. Escherichia coli O157:H7 was only sporadically recovered from sprout lots (three testing positive from 10 tested) derived from harvested beans. In contrast, Salmonella was recovered from 18 of 20 lots screened. Pathogens present on naturally contaminated seed could be success- fully inactivated with SOC applied at 200 ppm for 24 h at 28°C. SOC treat- ment could also decontaminate artificially inoculated mung bean batches containing different levels of contaminated seed. SOC inactivated E. coli O157:H7, but not Salmonella introduced onto damaged (scarified) beans. Conclusions: SOC sanitizer could inactivate Salmonella or E. coli O157:H7 nat- urally or artificially introduced onto mung beans. However, the SOC treatment failed to inactivate Salmonella introduced onto damaged mung beans. Significance and Impact of the Study: SOC sanitizer represents an effective method for decontaminating undamaged mung beans. Letters in Applied Microbiology ISSN 0266-8254 188 Journal compilation ª 2006 The Society for Applied Microbiology, Letters in Applied Microbiology 44 (2007) 188–193 ª 2006 The Authors