Fate of Escherichia coli O26 in corn silage experimentally contaminated at ensiling, at silo opening, or after aerobic exposure, and protective effect of various bacterial inoculants

Abstract

Shiga toxin-producing Escherichia coli (STEC) strains are responsible for human illness. Ruminants are recognized as a major reservoir of STEC, and animal feeds, such as silages, have been pointed out as a possible vehicle for the spread of STEC. The present study aimed to monitor the fate of pathogenic E. coli O26 strains in corn material experimentally inoculated (10⁵ CFU/g) during ensiling, just after silo opening, and after several days of aerobic exposure. The addition of 3 bacterial inoculants, Propionibacterium sp., Lactobacillus buchneri, and Leuconostoc mesenteroides (10⁶ CFU/g), was evaluated for their abilities to control these pathogens. The results showed that E. coli O26 could not survive in corn silage 5 days postensiling, and the 3 inoculants tested did not modify the fate of pathogen survival during ensiling. In the case of direct contamination at silo opening, E. coli O26 could be totally eradicated from corn silage previously inoculated with Leuconostoc mesenteroides. The combination of proper ensiling techniques and the utilization of selected bacterial inoculants appears to represent a good strategy to guarantee nutritional qualities of cattle feed while at the same time limiting the entry of pathogenic E. coli into the epidemiological cycle to improve the microbial safety of the food chain.

Fig. 1.

Schematic protocol for the study. P, Propionibacterium sp. strain R0410; LB, Lactobacillus buchneri NCIMB 40788; LM, Leuconostoc mesenteroides 6A1MLb4.

Fig. 2.

Evolution of pH values in all bag silos during the storage period (90 days).

Fig. 3.

Comparison of E. coli evolutions in Leuconostoc mesenteroides-treated silage immediately after opening or after 144 h of aerobic exposure for E. coli C1, C2, and C3 in independent silos A, B, and C.