Effects of the Dicarboxylic Acids Malate and Fumarate on E. coli O157:H7 and Salmonellaenterica Typhimurium Populations in Pure Culture and in Mixed Ruminal Microorganism Fermentations |
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Authors: | David J Nisbet Todd R Callaway T S Edrington Robin C Anderson and N Krueger |
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Institution: | (1) Food and Feed Safety Research Unit, Southern Plains Agricultural Research Center, Agricultural Research Service, USDA, College Station, TX 77845, USA |
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Abstract: | The dicarboxylic acids malate and fumarate increase ruminal pH, reduce methane production, increase propionate and total volatile
fatty acid (VFA) production, and reduce lactic acid accumulation in a manner similar to ionophores. These acids stimulate
the ruminal bacterium Selenomonas
ruminantium to ferment lactate to produce propionate. Thus, dicarboxylic acids have been suggested as nonantibiotic modifiers of the
ruminal fermentation, but their impact on ruminal microbial ecology remains unknown. This study was designed to examine what
effects these modifiers may have on intestinal pathogen populations such as Escherichia
coli O157:H7 and S.
enterica Typhimurium prior to their widespread incorporation into cattle rations. Pure cultures of E. coli O157:H7 strain 933 and S. enterica Typhimurium were grown with malate and fumarate added at 0, 1, 5, 10, and 20 mM (v/v; n = 3). Neither dicarboxylic acid inhibited (p > 0.1) the growth rate or final populations of E. coli O157:H7 or S. enterica Typhimurium. Ruminal fluid was collected from cattle (n = 2) and E. coli O157:H7 and S. enterica Typhimurium were added to separate ruminal fermentations incubated for 24 h at 39°C. Fumarate and malate were added at concentrations
of 0, 5, 10, and 20 mM (v/v; n = 2) and incubated for 24 h at 39°C. Malate or fumarate addition did not affect (p > 0.1) populations of E. coli O157:H7 or S. enterica Typhimurium. However, the final pH was increased (p < 0.05), the acetate:propionate ratio was decreased (p < 0.05), and the total VFA production was increased (p < 0.05) by ≥10 mM dicarboxylic acid addition. These results confirm that dicarboxylic acids can modify ruminal fermentation,
but they do not affect populations of critical foodborne pathogens.
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