Animals in a stable physiologic state are generally resistant to Salmonellosis due to what (molecular level)?

• A. enhanced antibody production
• B. higher body temperature
• C. increased saliva production
• D. production of butyric acid and other VFAs in sufficient concentrations to be bactericidal

Answer: (D)

In a stable physiologic state, the gut’s microbial fermentation products provide colonization resistance against Salmonella. Butyrate and other volatile fatty acids produced by anaerobic gut bacteria from dietary fibers accumulate in the lumen and can reach concentrations that are bactericidal. They lower the luminal pH and, more importantly, diffuse into Salmonella cells in their protonated form. Once inside, they dissociate, acidify the cytoplasm, and disrupt essential processes like energy production and enzyme function, leading to inhibited growth or cell death. This direct antimicrobial effect at the molecular level explains why these fatty acids help keep Salmonella in check when the animal is in a healthy, stable state. The other options don’t reflect this direct bacterial killing mechanism: antibody production is an immune response, fever is not typical of a stable state, and saliva production isn’t a major driver of Salmonella resistance in the gut.