Temperature and Biological Soil Effects on the Survival of Selected Foodborne Pathogens on a Mortar Surface

Abstract

The survival of three foodborne pathogens (Listeria monocytogenes, Yersinia enterocolitica, and Salmonella) attached to mortar surfaces, with or without biological soil (porcine serum) and incubated at either 4 or 10°C in the presence of condensate, was evaluated. Soiled and unsoiled coupons were inoculated by immersion into a five-strain cocktail (∼107 CFU/ml) of each organism type and evaluated. Coupons were incubated at 25°C for 2 h to allow attachment of cells, rinsed to remove unattached cells, and incubated at either 4 or 10°C at high humidity to create condensate on the surface. Sonication was used to remove the attached cells, and bacteria (CFU per coupon) was determined at 9 to 10 sampling periods over 120 h. Yersinia populations decreased more than 5 log units in the presence of serum in a 24-h period. Listeria and Salmonella had better survival on mortar in the presence of serum than Yersinia throughout the 120-h incubation period. Populations of L. monocytogenes declined more rapidly at 10 than at 4°C after 24 h. In general, differences in temperature did not affect the survival of Salmonella or Yersinia. Serum had a protective effect on the survival of all three organisms, sustaining populations at significantly (P ≤ 0.05) higher numbers over time than on corresponding unsoiled coupons. There were no significant differences (P > 0.05) among the mean number (CFU per coupon) of L. monocytogenes, Y. enterocolitica, or Salmonella on initial attachment onto the mortar surfaces (unsoiled). The results indicate relatively rapid destruction of selected pathogenic bacteria on unsoiled mortar surfaces compared with those that contained biological soil, thus highlighting the need for effective cleaning to reduce harborage of these microbes in the food factory environment.