Evaluation of inoculation method and inoculum drying time for their effects on survival and efficiency of recovery of Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes inoculated on the surface of tomatoes

• Published in: Journal of food protection Vol. 67; no. 4; pp. 732 - 741
• Main Authors: Lang, M.M, Harris, L.J, Beuchat, L.R
• Format: Journal Article
• Language: English
• Published: Des Moines, IA International Association of Milk, Food and Environmental Sanitarians 01.04.2004
• Subjects: antibacterial properties; bacteria attachment time; Bacterial Adhesion; bacterial contamination; Biological and medical sciences; Chlorine - pharmacology; Colony Count, Microbial; cross-strain inhibition; dipping; Disinfectants - pharmacology; drying; drying time; Escherichia coli; Escherichia coli O157 - growth & development; Escherichia coli O157 - physiology; Escherichia coli O157:H7; food contamination; Food engineering; Food industries; Food Microbiology; food pathogens; food sanitation; Fundamental and applied biological sciences. Psychology; General aspects; inoculation methods; inoculum; Listeria monocytogenes; Listeria monocytogenes - growth & development; Listeria monocytogenes - physiology; Lycopersicon esculentum; pathogen survival; plate count; potassium phosphates; ripening; Salmonella; Salmonella - growth & development; Salmonella - physiology; sanitizing; sodium hypochlorite; Solanum lycopersicum - microbiology; solutions; spot method; spraying; surface area; Time Factors; tomatoes; viability; water; Evaluation; Salmonella; Vegetables; Escherichia coli; Listeria monocytogenes; Method; Recovery; Survival; Surface; Inoculation; Efficiency; Dicotyledones; Angiospermae; Lycopersicon esculentum; Bacteria; Spermatophyta; Solanaceae; Enterobacteriaceae; Drying
• ISSN: 0362-028X; 1944-9097
• DOI: 10.4315/0362-028X-67.4.732

A study was undertaken to evaluate methods for applying inoculum and to examine the effect of inoculum drying time on survival and recovery of foodborne pathogens inoculated onto the surface of raw, ripe tomatoes. Five-strain mixtures of Escherichia coli O157:H7, Salmonella, or Listeria monocytogenes were applied to tomatoes by dip, spot, or spray inoculation methods. Inocula were dried for 1 or 24 h at 22°C before tomatoes were treated with water (control) or chlorine (200 micrograms/ml). Significantly (α = 0.05) larger populations (CFU per tomato) of E. coli O157:H7 and Salmonella were recovered from dip-inoculated tomatoes than from spot- or spray-inoculated tomatoes. This difference was attributed to larger numbers of cells adhering to tomatoes subjected to dip inoculation. Populations of E. coli O157:H7 and Salmonella recovered from spot- and spray-inoculated tomatoes containing the same initial number of cells were not significantly different. Significantly different L. monocytogenes population sizes were recovered from inoculated tomatoes (dip > spot > spray). Populations of pathogens recovered from tomatoes were significantly larger when inocula were dried for 1 h compared with 24 h. Significant differences (water > chlorine) were observed in the sizes of populations for all pathogens recovered from tomatoes treated with chlorine, regardless of inoculation method or drying time. Results indicate that inoculation method, drying time, and treatment affect survival and/or recovery of foodborne pathogens inoculated onto the surface of tomatoes. We recommend that spot inoculation with a drying time of 24 h at 22°C be used with standard methods to determine the efficacy of chlorine and other sanitizers for killing foodborne pathogens on tomatoes.