Survival of Non-O157 STEC and Escherichia coli O157:H7 during the Manufacture of Dry Fermented Sausages

Introduction: In response to E. coli O157:H7 outbreaks associated with DFS, regulatory agencies require processors to validate their production processes to demonstrate a 5-log reduction in E. coli O157:H7 numbers. More recently, non-O157 STEC have been responsible for outbreaks linked to fermented sausages.

Purpose: Compare the survival of the top six non-O157 STEC with E. coli O157:H7 during the manufacture of DFS.

Methods: Batches of uninoculated sausages and sausages containing individual strain of serotype O26, O103, O45, O111, O121, O14 and O157 at 10⁷ CFU/g were produced. The sausages were subjected to fermentation (48 h) followed by ripening (72 h) and drying (34 days) to obtain dry salami. Microbiological (STEC and total plate counts), pH, a_w and MPr changes were monitored during the 39-day process. Changes in STEC numbers were analyzed by ANOVA for significance among serotypes and regression analysis to determine the rate of pathogen reduction.

Results: All serotypes showed a minimum of 5-log reduction in numbers by the end of the 39-day curing process. Significant pathogen reduction happened in the 48-h fermentation step (P < 0.0001), when the pH dropped from 5.6 to 4.7. Serotype O45 showed the highest reduction (1.95 log), while O26 had the least (0.97 log) reduction. The 72-h ripening step resulted in less than 1-log reduction. Regression analysis revealed that the most rapid pathogen reduction happened during the fermentation step followed by a slow but consistent reduction during the 34-day drying, with variation between serotypes, for example, O45 and O145 could not be enumerated past 27 days, while O157, O111 and O103 could be enumerated at 34 days even after the a_w had reached 0.80.   

Significance: The results indicate that DFS manufacturing processes validated to demonstrate a 5-log reduction of E. coli O157:H7 could result in a similar reduction of the top six non-O157 STEC serotypes.