Submitted to: Current Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/23/2008
Publication Date: 5/1/2009
Citation: Nisbet, D.J., Callaway, T.R., Edrington, T.S., Anderson, R.C., Krueger, N.A. 2009. Effects of the dicarboxylic acids malate and fumarate on E. coli 0157:H7 and Salmonella enterica Typhimurium populations in pure culture and in mixed ruminal microorganism fermentations. Current Microbiology. 58:488-492. Interpretive Summary: The dicarboxylic organic acids malate and fumarate have been suggested for use as modifiers of the ruminal fermentation of cattle because they enhance the efficiency of this fermentation, resulting in more efficient meat or milk production. These acids have effects similar to that of the ionophore monensin on the ruminal fermentation. However, some organic acids can affect intestinal populations of foodborne pathogenic bacteria such as E. coli O157:H7 and Salmonella that are found in cattle. In our study, we found that the addition of the dicarboxylic acids did improve the overall energetic efficiency of the mixed ruminal microorganism fermentation, but did not affect populations of E. coli O157:H7 and Salmonella that were added to these fermentations. These results confirm that dicarboxylic acids can modify the ruminal fermentation, but they do not influence populations of critical foodborne pathogens.
Technical Abstract: The dicarboxylic organic acids malate and fumarate increase ruminal pH, reduce methane production, increase propionate and total 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 for use as non-antibiotic modifiers of the ruminal fermentation, but their impact on the overall microbial ecology of the rumen remains unknown. Therefore, this study was prepared to determine the effects of these modifiers on populations of the foodborne pathogens, Escherichia coli O157:H7 and Salmonella Typhimurium. Pure cultures of E. coli O157:H7 strain 933 and S. 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 greater than 0.1) the growth rate or final populations of E. coli O157:H7 or S. Typhimurium. Ruminal fluid was collected from concentrate fed cows (n = 2), and E. coli O157:H7 and S. Typhimurium were added to separate ruminal fermentations. Fumarate and malate were added at concentrations of 0, 5, 10, and 20 mM (v/v; n = 2) and were incubated for 24 h. Malate or fumarate addition did not affect (P greater than 0.1) populations of E. coli O157:H7 or S. Typhimurium. However, final pH was increased (P less than 0.05), the acetate:propionate ratio was decreased (P less than 0.05), and total VFA production was increased (P less than 0.05) by greater than 10 mM dicarboxylic acid addition. These results confirm that dicarboxylic acids can modify the ruminal fermentation, but they do not influence populations of critical foodborne pathogens.