Fecal Shedding and Rumen Growth of Escherichia coli O157:H7 in Fasted Calves

Abstract

Nine weaned calves aged from 8 to 12 weeks were fitted with rumen cannulas and were inoculated by cannula with 10(10) CFU of a five-strain mixture of nalidixic acid-resistant Escherichia coli O157:H7. Six calves were fasted for 48 h on days 15 and 16 and days 22 and 23 after inoculation. Samples of rumen contents and feces were obtained daily to enumerate E. coli O157:H7 populations and to determine rumen volatile fatty acid (VFA) concentrations and rumen pH. Fasting resulted in a marked decrease in rumen VFA concentrations from a mean of 135 mmol/liter before the fast to a mean of 35 mmol/liter during the second day of the fast. However, there was no correlation between daily VFA concentration and daily rumen or fecal numbers of E. coli O157:H7 in any of the calves. Fasting generally had no significant effect on the rumen or fecal numbers of E. coli O157:H7. The exception was a single fasted calf that experienced a 3-log(10) CFU/g increase in fecal shedding during and after the first fast. Despite the consistent changes in VFA concentrations in fasted calves, the fluctuations in rumen numbers of E. coli O157:H7 in the rumen of fasted calves were minimal. At the end of the experiment, E. coli O157:H7 was detected in either the rumen or omasum in two of three control calves at necropsy and in either the rumen or reticulum in five of six fasted calves. E. coli O157:H7 was detected in the colon in two of three control calves and in six of six fasted calves at necropsy. These results suggest that in cattle already shedding E. coli O157:H7, feed withdrawal and the associated changes in rumen pH and VFA concentrations have little effect on fecal shedding and rumen proliferation of E. coli O157:H7.

Transmission and control of Escherichia coli O157:H7 — A review

“…Tkalcic et al (2000) observed more extensive proliferation of E. coli O157:H7 in vitro in ruminal fluid from cattle fed a high roughage diet than a high concentrate diet, but did not observe this effect in vivo. Harmon et al (1999) also found no correlation between daily fluctuations in ruminal VFA concentrations and ruminal or fecal E. coli O157:H7 numbers. In feces, the percentage of E. coli that were acid tolerant was higher with concentrate-fed cattle than with those fed hay (DiezGonzalez et al 1998).…”

Enterohaemorrhagic Escherichia coli: emerging issues on virulence and modes of transmission

“…The effect of fasting has also been investigated, and shown to have only a little effect on faecal shedding and rumen proliferation of EHEC O157 in calves [69].…”

The potential for the control ofEscherichia coliO157 in farm animals

“…This period may allow the opportunity for providing easily assimilated supplements, possibly non-therapeutic antimicrobial compounds or specific bacterial strains, which could provide short-term protection against excessive proliferation of E. coli 0157, thus reducing the risks of contamination of meat in the slaughterhouse. In this respect, the recent demonstration of a protective effect of a 'probiotic' mixture of strains of commensal E. coli and Proteus mirabilis is significant (Zhao et al 1998;Harmon et al 1999). Most fundamentally, clarifying the mechanisms involved in the survival of E. coli in the presence of weak acids could pro-vide both simple and effective methods of disinfection, and fresh insights into the ecology of this notorious pathogen.…”

“…Hancock et al (1994) found no difference in the prevalence of E. coli 0157 between grain-and hay-fed animals. Harmon et al (1999) reported the results of experiments involving the experimental infection of calves receiving a Flg.3 Effect of esculin (5mmol T") on the survival of Escherichia coli 0157 strain 12900 in rumen contents containing mixed rumen micro-organisms (0 = control, • = 5mmoll~l esculetin) (Duncanet al 1998) …”

“…The role of colicins in the ecology of E. coli is an area of active investigation (Gordon and Riley 1999), but the significance of colicins in rumen microbial ecology has not been studied. Administration of an inoculum containing strains of E. coli and Proteus mirabilis has been shown to reduce shedding of E. coli 0157 by experimentally-infected calves (Zhao et al 1998;Harmon et al 1999), but the mechanisms of the microbial interactions involved are not known.…”