Differential growth of Campylobacter jejuni in mixed populations of porcine fecal, bovine fecal, or bovine ruminal microbes

Campylobacter is a leading bacterial cause of human foodborne illness in the United States. Campylobacter are found more frequently and at higher numbers in the intestinal tract than in the rumen. This suggests Campylobacter, which occupy an amino acid-fermenting niche, may be less competitive in the rumen due to resident populations of competent amino acid-fermenting and ammonia-assimilating microbes. To test this hypothesis, rumen and fecal samples, collected freshly from a cannulated cow, and freshly collected feces from a market hog were each diluted 10⁻⁴ in anaerobic buffer to deplete endogenous substrate. The populations were tested individually or jointly by inoculating each of the diluted suspensions alone (0.2 mL) or in pairs (0.1 mL each) to tubes containing 10⁵ cfu of C. jejuni in Bolton broth augmented with 0.2% glucose, cellobiose, and xylose. Total anaerobes measured before inoculation were 4, 3, and 4 log₁₀ cfu/mL in rumen, bovine fecal, and porcine fecal mixtures, respectively and contained no wildtype Campylobacter. Results revealed that after 48 h of anaerobic incubation (39°C), C. jejuni were lowest (P < 0.05) in cultures inoculated with suspensions of rumen microbes alone or rumen:bovine fecal mixtures (5.7 and 6.4 log₁₀ cfu/mL, respectively). Campylobacter jejuni were highest (P < 0.05) in cultures inoculated with swine fecal suspensions alone or control C. jejuni cultured without any of the suspensions (8.0 and 8.3 log₁₀ cfu/mL, respectively) and intermediate in the other tested cultures (7.2 to 7.6 log₁₀ cfu/mL). Ammonia accumulations were higher (P < 0.05) in C. jejuni cultures inoculated with porcine fecal:bovine fecal, rumen:porcine fecal mixtures and porcine fecal suspensions alone (8.2, 8.1 and 6.3 µmol/mL, respectively) than in the other cultures (<1.9 µmol/mL). At 48 h, total anaerobes in cultures inoculated with the mixed gut microbes differed modestly (P < 0.05), ranging from 7.1 to 7.7 log10 cfu/mL. Results warrant further study to characterize population differences in amino acid metabolism that may affect growth of C. jejuni in rumen and fecal sources.

Key Words: Campylobacter, food safety, rumen, swine.

Published in the proceedings of the 10th Symposium on Gut Health in Production of Food Animals 2022, St. Louis, USA.