|HARLOW, BRITTANY - University Of Kentucky|
|LAWRENCE, LAURIE - University Of Kentucky|
Submitted to: Congress on Gastrointestinal Function
Publication Type: Abstract Only
Publication Acceptance Date: 3/30/2015
Publication Date: 4/13/2015
Citation: Harlow, B.E., Lawrence, L.M., Flythe, M.D. 2015. Amylolytic bacteria in the equine hindgut: Effect of starch source and a case for antimicrobial-mediated competition. Congress on Gastrointestinal Function. Pgs. 45-46.
Technical Abstract: Cereal grains are often included in equine diets. A high proportion of grain in the diet can allow starch to reach the hindgut where bacteria compete for the substrate, produce lactic acid and decrease pH. The ecological theory of niche predicts that competition for a resource will negatively impact one or more of the competing organisms. The hypothesis of an earlier study was that starch introduction would cause a source-dependent press disturbance in the equine fecal microbial community, most notably in resident starch-utilizing (SU) populations. Feces were collected from horses and cell suspensions were prepared by differential centrifugation and re-suspension in media with ground corn or oats as the substrate. SU, Lancefield group D Gram-positive cocci (GDGPC), and lactobacilli were enumerated after 24 h. Corn had >104-fold more SU, >10-fold more GDGPC, and >100-fold fewer lactobacilli than oats. Isolates from the highest dilutions of SU were identified by their 16S RNA gene sequence as Enterococcus faecalis and Streptococcus bovis in corn and oats, respectively. In an in vivo experiment, 10 horses were assigned to a corn (n = 5) or an oats diet (n = 5). Horses were gradually adapted to their final starch intake (3 g/kg BW/d) for 14 d. After 13 d, corn horses had 104-fold more SU, >10-fold more GDGPC, and >10-fold fewer lactobacilli than oat horses. The predominant SU isolates from corn horses were again E. faecalis. Both experiments identified a negative correlation between lactobacilli and SU, indicating a potential competition between these bacteria for starch (R2 = 0.89, in vitro; R2 = 0.95, in vivo). The next experiment was conducted to determine if a Lactobacillus addition would mitigate SU proliferation, specifically GDGPC, with corn fermentation. The in vitro experiment was conducted as described above with ground corn ± live or dead (autoclaved) L. reuteri. The addition of live or dead L. reuteri decreased SU and GDGPC by >104- and 100-fold at 24 h, respectively. To identify the mechanism of action, an energized E. faecalis isolate was co-incubated with dead L. reuteri cells or supernatant. The supernatant depleted the intracellular K+ of E. faecalis in less than 10 min of exposure. This result demonstrates that one aspect of competition between lactobacilli and enterococci could be a membrane active antimicrobial.