Growth of Escherichia coli O157 in poorly fermented laboratory silage:: a possible environmental dimension in the epidemiology of E-coli O157

Laboratory silages, inoculated with either c. 1000 cfu g(-1), an atoxigenic Escherichia coli O157 or a toxigenic E. coli O157 isolate, were made in plastic bags which permitted limited aerobic spoilage. Replicate bags of each treatment were opened at weekly intervals after incubation at 20 degrees C. In all silages the fermentation was slow and aerobic spoilage with visible moulding occurred at the tie ends after 7 d. In all the aerobically spoiled silages Enterobacteriaceae reached over 10(7) cfu g(-1) within 1 week. The E. coli in control silages increased from barely detectable levels to 10(+) cfu g(-1) within 13 d; over the same period both strains of E. coli O157 increased from 10(3) to 10(7) cfu g(-1). The increases in the poorly fermented interior of the silage bags were initially; similar but declined slightly as the pH fell. It is suggested that faecal contamination of grass followed by poor silage management may be a factor in the persistence of E. coli O157 carriage in ruminants.