Comparison of the fate of the top six non-O157 shiga-toxin producing Escherichia coli (STEC) and E. coil O157:H7 during the manufacture of dry fermented sausages

The study examined the relative fate of the top six non-O157 shiga-toxin producing Escherichia coil (STEC) and E. coli O157:H7 during the manufacture of dry fermented sausages (DFS). Three separate batches of sausages containing a five-strain cocktail for each serogroup and uninoculated control were manufactured and subjected to identical fermentation, maturation and dry curing conditions. Changes in physicochemical properties and inoculated STEC numbers were enumerated during the DFS production stages and log reduction and log reduction rates were calculated. Inoculation of very high concentrations (8 log CFU g(-1)) of STEC in the sausage batter did not significantly (P > 0.05) affect the changes in the pH, aw, moisture, protein, fat content compared to the uninoculated DFS. There was a significant (P < 0.05) reduction in counts within the 48 h fermentation for all STEC serogroups inoculated by about 0.97-to 1.42-log units. However, during the sausage maturation stage, all serogroups except 0121 and 045 showed a significant reduction in numbers. During the extended 34 day drying stage, all STEC serogroups showed a significant reduction in counts reaching a 5-log reduction within 20 to 27 days of drying. ANOVA of the log reduction rates revealed significant differences in the reduction rates among the STEC serogroups examined. During the fermentation stage, serogroup 045 had the highest reduction rate at 0.98-log CFU g(-1) day(-1) which was significantly higher compared to all other STEC serogroups (P < 0.05), while 026 was the most tolerant to the conditions encountered during the fermentation stage with a reduction rate of 0.49-log CFU g(-1) day(-1). However, during the extended 34 days drying stage all STEC serogroups showed a steady reduction in population with a reduction rate ranging from 0.11-to 0.18 log CFU g(-1) day(-1). The log reduction rate of E. colt O157:H7 was similar to that of serogroups 0111 and 0103, but was significantly lower (P < 0.05) than all other STEC serogroups examined in the study. The log reduction rates of serogroups 0121, 045, 0145 and 026 during drying were not significantly different (P > 0.05) from each other. These results indicate that the lethality of DFS production processes observed against E. coil O157:H7 would result in a similar inactivation of the top six non-O157 STEC.