Some studies of the in vitro effect of bovine rumen fluid on the growth of Salmonella Typhimurium

Abstract

A study of some factors affecting the survival of salmonellae in the rumen of trie bovine animal was made.

A Friesian cow was fed once daily on a maintenance allowance of 7.0 Kg. crushed barley and 2.0 Kg. hay. In each of four trials food was withheld for a period of forty-eight hours and rumen fluid samples were taken four-and-a-half hours after feeding, at the end of the starvation period and four-and-a-half hours after feeding was resumed.

Solutions containing equal quantities of nutrient broth and either sterilised rumen fluid or distilled water were adjusted to the pH of the rumen samples.

The prepared solutions were inoculated with a drop of twenty-four hour Salmonella typhimurium culture and then incubated aerobically for twenty-four hours at 37°C. Viable counts in the solutions were made before and after incubation. Volatile fatty acid and lactate concentrations, as well as pH values, were determined in all rumen fluid samples taken during the trials.

Ratios of viable counts after incubation to before incubation were calculated for control solutions without rumen fluid and test solutions containing rumen fluid. These ratios were found to be significantly lower in solutions containing rumen fluid sampled four-and-a-half hours after regular feeding than in solutions without rumen fluid. No significant difference was found between the ratios in test and control solutions using either rumen fluid sampled after forty-eight hours starvation or four-and-a-half hours after resumption of normal feeding.

Mean total volatile fatty acid concentrations were significantly higher in rumen fluid samples taken four-and-a-half hours after regular feeding than in those taken after forty-eight hours starvation, or four-and-a-half hours after feeding was resumed. The mean concentrations of total butyric and n-butyric acids in rumen samples taken four-and-a-half hours after regular feeding were significantly higher than in samples taken after forty-eight hours starvation or four-and-a-half hours after feeding was resumed. No difference between the latter two mean concentrations was found.

Differences in mean lactate concentrations in rumen fluid samples were not statistically significant.

It is concluded that a solution containing 50% sterilised rumen fluid, taken from a cow four-and-a-half hours after the last regular feed of 7.0 Kg. barley and 2.0 Kg. hay, had a significant inhibitory effect on the growth of S. typhimurium in vitro. No such effect was demonstrated on this growth when rumen fluid taken from the cow either after forty-eight hours starvation or four-and- a-half hours after resumption of feeding was used. This effect is considered to be partially due to the volatile fatty acids in the rumen fluid and in particular n-butyric acid.

The importance of these results is discussed as well as their relationships to some earlier findings reported in the literature.