P-032. Growth and Survival of Acid-Resistant and Non Acid Resistant Shiga Toxin Producing Escherichia coli (STEC) Strains in Experimentally Contaminated French Sausages

M-P. Montet1, V. Coppet2, S. Ganet1, M-L. Delignette-Muller1, S. Christieans2, S. Miszczycha1, D. Thevenot1, C. Vernozy-Rozand1;
1ENVL, Marcy l'Etoile, FRANCE, 2ADIV, Clermont Ferrand, FRANCE.

Background: Both pathogenic and nonpathogenic E.coli exhibit a stress response to sublethal environmental stresses. The nature and the intensity of the stress response may vary between pathogenic and nonpathogenic E.coli and between strains of pathogenic E.coli. Several studies have reported acid tolerance and survival characteristics of E.coli O157:H7 in foods, but there are few reports about the tolerance to organic acids in foods by non O157:H7 (STEC) serogroups. The purpose of this study was to examine the effect of the manufacturing process of French sausages on the growth and survival of acid resistant (AR) and non acid resistant (NAR) STEC strains. Methods: The six strains, 3 acid resistant (AR) and 3 non acid resistant (NAR) were inoculated separately, in raw mixing sausage at a level of 104 CFU/g. . A total of 26 batches of sausages were manufactured, 8 of them was not inoculated and served as negative control. No STEC was detected in the raw materials: pork meat, pork fat and natural casing, before the challenge testing. Results: A rapid decrease in the number of STEC strains AR and NAR was observed during the 5 first days of fermentation at 24°C (1.5 log10CFU/g and 1 log10 CFU/g for AR and NAR STEC strains respectively). This rapid decrease was followed by a more gradual but continuous decrease observed during drying at 14°C (until day 35) (1 log10 CFU/g and 3 log10 CFU/g for AR and NAR STEC strains respectively). The counts of all NAR STEC were below the detection limit of the method used (ie: 10 CFU/g) after 30 days of drying but STEC couldn’t be detected after an enrichments step. The counts of STEC were, between 1 to 10 CFU/g after 25 days of drying for NAR STEC and only at the best before date (day 60) for AR STEC. It was not possible to detect NAR STEC even after an enrichment step at day 60. Conclusion: Though the fermentation and/or the drying of the product can reduce the risk of the presence of foodborne pathogens, in many cases they do not eliminate them completely. The present study showed that process of manufacture French sausages only caused a full destruction of NAR STEC after 60 days of drying and storage of sausages.