| Antibiotic-associated diarrhea (AAD) is a common and potentially fatal disorder in horses and is often attributable to Salmonella spp. Disturbances in anaerobic microflora are thought to cause altered intestinal levels of bacteriostatic short-chain fatty acids (SCFA). Salmonella virulence plasmid (spv) genes are reported to increase ability of Salmonella to grow in organs outside the gastrointestinal tract. Horses treated with intravenous oxytetracycline (TET), oral trimethoprim-sulfamethoxazole (TMPS), and intramuscular ceftiofur (NAX) had significant differences in concentrations of seven individual cecal SCFA with TET having the most significant effects, followed by TMPS and NAX. No differences were detected in cecal protozoal counts, total culturable cecal anaerobes, or cecal pH compared to untreated horses.; Epidemiological techniques were used to investigate 106 cases of salmonella infection in horses at a veterinary teaching hospital over 2 years. Total mortality was 36.5%. Plasmid profiles, spv gene analysis, serovar, and antibiotic sensitivity data were recorded for all isolates. Odds ratios predicted an increased risk of a fatal outcome in horses younger than 4 years of age (3.3 times), horses infected with group B salmonellae (15.7 times relative to group D), and horses whose salmonella isolate possessed the spv genes (12.3 times). Extra-intestinal salmonella isolates were 12.2 times more likely to contain the spv genes. The majority of large plasmids in salmonella serovars isolated from horses were not virulence plasmids, but likely antibiotic resistance plasmids (3/3 tested transferred multiple resistances). This information suggests that the spv genes may play a similar role in horses as they do in humans, mice, and calves: to potentiate systemic infection after gastrointestinal infection.; Sterile-filtered cecal liquor from horses treated with ceftiofur or trimethoprim-sulfamethoxazole increased the in vitro anaerobic growth rates of Salmonella relative to plain media, and slightly more than untreated control horses cecal liquor. Salmonella grew equally as well (but much slower than NAX or TMPS) in TET treated horses cecal liquor and plain M9 medium. The SCFAs acetate, butyrate, and propionate, added to M9 minimal medium at 30mM or 100mM, exhibited a dose-dependent inhibition of anaerobic salmonella growth that was not attributable to the spv genes, with propionate 100mM > butyrate 100mM > acetate 100mM ≈ propionate 34mM > butyrate 30mM > acetate 30mM. |
