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Experimental Biology and Medicine 228:365-369 (2003)
© 2003 Society for Experimental Biology and Medicine

SUPPLEMENT. FOOD SAFETY CONCERNS OF VEROTOXIN-PRODUCING ESCHERICHIA COLI

Influence of pH Treatments on Survival of Escherichia coli O157:H7 in Continuous Cultures of Rumen Contents

Brandolyn H. Thran*, Hussein S. Hussein*,1, Doug Redelman{dagger} and George C.J. Fernandez{ddagger}

* Department of Animal Biotechnology,
{dagger} Cytometry Center, and
{ddagger} Nevada Agricultural Experiment Station, University of Nevada, Reno, Nevada 89557

Abstract

The pH (i.e., 5.5, 5.75, 6.0, 6.25, 6.5, 6.75, 7.0, and 7.25) effect on Escherichia coli O157:H7 in an artificial rumen model was investigated. Eight fermenters were inoculated with bovine rumen fluid and were supplied with a diet (75 g of dry matter daily in 12 equal portions [every 2 hr]) containing similar forage-to-concentrate ratio. After an adaptation period (i.e., 3 days for adjusting the rumen fluid [pH 6.2] microbial population to the test pH and 4 days for adjustment to the diet at the test pH), each fermenter was inoculated with 109 cells of E. coli O157:H7. Samples were collected hourly for 12 hr and every 2 hr for an additional 12 hr and were analyzed by flow cytometer. E. coli O157:H7 could not be quantified after 24 hr, and detection was only possible after enrichment. Because the pathogen could not be detected 5 days postinoculation (i.e., Day 13), the fermenters were reinoculated with E. coli O157:H7 on Days 17 and 22. E. coli O157:H7 numbers decreased from 106 to 104/ml of fermenter contents in a quadratic (P < 0.05) fashion over the 24-hr sampling period, and the rate of reduction was slower (P < 0.05) for pH 7.0 than for other pH treatments. Results suggested that E. coli O157:H7 population were decreased by competitive exclusion and were not affected by culture pH.

Key Words: Escherichia coli • cattle • continuous culture • food-borne pathogens




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J. T. Fox, J. S. Drouillard, X. Shi, and T. G. Nagaraja
Effects of mucin and its carbohydrate constituents on Escherichia coli O157 growth in batch culture fermentations with ruminal or fecal microbial inoculum
J Anim Sci, April 1, 2009; 87(4): 1304 - 1313.
[Abstract] [Full Text] [PDF]


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