title: Dynamic effects of free chlorine concentration, organic load, and exposure time on the inactivation of Salmonella, Escherichia coli O157:H7, and non-O157 Shiga toxin-producing E. coli.
abstract: This study evaluated the dynamic effects of free-chlorine (FC) concentration, contact time, and organic load on the inactivation of Salmonella, Escherichia coli O157:H7, and non-O157 Shiga toxin-producing E. coli (STEC) in suspension. Bacterial cells from four strains each of Salmonella, E. coli O157:H7, and non-O157 STEC were inoculated separately or as a multistrain cocktail into solutions with varying FC concentrations. Lettuce or tomato extract was used to simulate the organic matter present during commercial fresh and fresh-cut produce wash operations. After exposure to FC for various lengths of time, the bacterial survival and water-quality changes were determined. In the absence of organic matter in a wash solution, pathogen inactivation is primarily a function of initial FC concentration (P < 0.0001), exposure time (P < 0.0001), and pathogen strains (P < 0.0001). In general, an over 4.5-log CFU/ml pathogen reduction was found after exposure to >0.5 mg/liter FC for over 30 s, or to >1.0 mg/liter FC for over 5 s. When the combination of FC concentration and contact time were less than or equal to the above conditions, survival of pathogens was strain dependant and ranked as: Salmonella > E. coli O157:H7 > non-O157 STEC. When organic matter was present in the wash solution, pathogen inactivation efficacy was specifically dependent on the residual FC concentration, which directly relates to both the initial FC concentration and the organic load. Prevention of pathogen survival in chlorinated produce wash solutions can be achieved by maintaining sufficient FC concentration and reducing the accumulation of organic matter.
authors: U.S. Department of Agriculture, Agricultural Research Service, Environmental Microbial and Food Safety Laboratory, 10300 Baltimore Avenue, Beltsville, Maryland 20705, USA.
authors: Cangliang
authors: C
authors: Shen
authors: Yaguang
authors: Y
authors: Luo
authors: Xiangwu
authors: X
authors: Nou
authors: Qin
authors: Q
authors: Wang
authors: Patricia
authors: P
authors: Millner
mesh_terms: D002713:Chlorine / Q000494:pharmacology*; D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D004202:Disinfectants / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D019453:Escherichia coli O157 / Q000187:drug effects* / Q000254:growth & development; D005506:Food Contamination / Q000517:prevention & control; D006801:Humans; D012475:Salmonella / Q000187:drug effects* / Q000254:growth & development; D054323:Shiga-Toxigenic Escherichia coli / Q000187:drug effects* / Q000254:growth & development; D013997:Time Factors; D014871:Water Microbiology
chemical_list: D004202:Disinfectants; D002713:Chlorine