The purpose of this study was to compare the effects of humidity on the preharvest survival of microbial pathogens on cantaloupe, lettuce, and bell peppers. An additional goal was to evaluate Clostridium perfringens as an indicator of fecal contamination on produce. The microorganisms used in this study included Escherichia coli, E. coli O157:H7, Shigella sonnei, Salmonella enterica subsp. enterica, Clostridium perfringens, hepatitis A virus (HAV), feline calicivirus (FCV), and coliphage PRD1. The study took place in a controlled environment chamber that allowed for the control of temperature (18 to 26°C) and relative humidity. Survival rates under high (mean, 85.7 to 90.3%) and low (mean, 45.1 to 48.4%) relative humidity were compared. The surfaces of the edible portion of each plant were inoculated with the study microorganisms. Samples were collected throughout 2 weeks. More microorganisms survived significantly longer (P < 0.05) on cantaloupe than on lettuce and bell peppers. The type of produce on which each organism experienced the highest inactivation rate tended to change with relative humidity. The survival of microorganisms on produce surfaces was not uniformly affected by relative humidity. Of the studied microorganisms, HAV, PRD1, and C. perfringens were found to have the lowest inactivation rates, whereas FCV and E. coli ATCC 25922 tended to become inactivated most rapidly. C. perfringens generally survived longer than all other bacteria and FCV in all experiments. This trend suggests that C. perfringens may be an acceptable indicator of bacterial contamination and survival in various environments and on different types of crops.
† Present address: Department of Biological Sciences, University of North Texas, Denton, TX 76203-5220.