PARENT SESSION
Poster Session 24: Agro-Ecology
Wednesday, August 10, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal
Influence of temperature fluctuations on Salmonella typhimurium and E. coli O157:H7 survival in manure.
Semenov, Alexander*,1, van Bruggen, Ariena1, Semenov, Alexander2, van Overbeek, Leo3, Termorshuizen, Aad1, 1 Biological Farming Systems, Wageningen, the Netherlands2 Dept. of Microbiology, Moscow, Russia3 Plant Research International B.V., Wageningen, the Netherlands
ABSTRACT- To minimize pathogen spread and survival in the vegetable production chain, we investigated the effects of temperature on survival of Salmonella typhimurium and E. coli O157:H7 in manure, the main source of enteropathogens. The effects of constant temperatures on enteropathogens have been investigated extensively, but the possible influence of temperature changes on survival of enteropathogens is still unclear. Effects of 4 average temperatures (7, 16, 23 and 33C) and sine oscillations with 3 amplitudes (0, 4, 7C) on survival of gfp-marked strains of S. typhimurium and E. coli O157:H7 in manure were investigated in small microcosms. Manure was inoculated with the pathogens at 107 - 108 cells/gram of dry manure. Samples were collected immediately after inoculation, and after 1 and 2 weeks for E. coli O157:H7 and 2 and 3 weeks for S. typhimurium. Population densities were determined by dilution plating and direct counting. In addition, evolved gases (O2, N2 and CO2) and total bacterial CFUs were determined. S. typhimurium survived for longer periods than E. coli O157:H7. Survival of both pathogens declined with increasing mean temperatures and with increasing amplitude in daily temperature fluctuations (on average a 1.7 times shorter survival at an amplitude of 4C and 2.8 times shorter at 7C compared to non-fluctuating temperatures). The main mathematical explanation is probably non-linearity of the temperature response with a relatively greater sensitivity to temporarily higher temperatures compared to temporarily lower temperatures than the mean temperature. The main physiological explanation could be greater stress and energy expenditure after increasing temperatures than after decreasing temperatures. In conclusion: responses of enteropathogens to fluctuating temperatures cannot be deduced from temperature relationships determined under constant temperatures.
Key words: human enteric pathogens, temperature oscillations, cattle manure, survival