Effects of diet on rumen proliferation and fecal shedding of Escherichia coil O157:H7 in calves.
Calves inoculated with Escherichia coli O157:H7 and fed either a high-roughage or high-concentrate diet were evaluated for rumen proliferation and fecal shedding of E. coli O157:H7. Calves fed the high-roughage diet had lower mean rumen volatile fatty acid concentrations and higher rumen pH values than did calves fed the high-concentrate diet. Despite these differences in rumen conditions, the calves fed the high-roughage diet did not have greater rumen populations of E. coli O157: H7 and did not exhibit increased or longer fecal shedding compared with the calves fed the high-concentrate diet. Two calves shedding the highest mean concentrations of E. coli O157:H7 were both fed the high-concentrate diet. There was a significant (P < 0.05) positive correlation between fecal shedding and rumen volatile fatty acid concentration in calves fed a high-concentrate diet. The effects of diet on E. coli O157:H7 proliferation and acid resistance were investigated using an in vitro rumen fermentation system. Rumen fluid collected from steers fed a high-roughage diet, but not from steers fed a high-concentrate diet, supported the proliferation of E. coli O157:H7. Rumen fluid from steers fed a high-concentrate diet rapidly induced acid resistance in E. coli O157:H7. The impact of diet on fecal shedding of E. coli O157:H7 is still unclear and may depend on dietary effects on fermentation in the colon and on diet-induced changes in the resident microflora. However, rapid development of acid tolerance by E. coli O157:H7 in the rumens of calves fed high-concentrate diets, allowing larger populations to survive passage through the acidic abomasum to proliferate in the colon, may be one factor that influences fecal shedding in cattle on feed.
Tkalcic
S
S
Department of Pathology, College of Veterinary Medicine, University of Georgia, Athens 30602, USA.
Brown
C A
CA
Harmon
B G
BG
Jain
A V
AV
Mueller
E P
EP
Parks
A
A
Jacobsen
K L
KL
Martin
S A
SA
Zhao
T
T
Doyle
M P
MP
D000821:Animal Feed; D000818:Animals; D002417:Cattle / Q000382:microbiology*; D015169:Colony Count, Microbial; D004032:Diet / Q000662:veterinary*; D004043:Dietary Fiber / Q000008:administration & dosage; D019453:Escherichia coli O157 / Q000254:growth & development* / Q000502:physiology; D005243:Feces / Q000382:microbiology*; D005285:Fermentation; D006863:Hydrogen-Ion Concentration; D012417:Rumen / Q000382:microbiology*; D013997:Time Factors