Iron acquisition pathways and colonization of the inflamed intestine by Salmonella enterica serovar Typhimurium

Salmonella enterica serotype Typhimurium is able to expand in the lumen of the inflamed intestine through mechanisms that have not been fully resolved. Here we utilized streptomycin-pretreated mice and dextran sodium sulfate (DSS)-treated mice to investigate how pathways for S. Typhimurium iron acquisition contribute to pathogen expansion in the inflamed intestine. Competitive infection with an iron uptake-proficient S. Typhimurium strain and mutant strains lacking tonB feoB, feoB, tonB or iroN in streptomycin pretreated mice demonstrated that ferric iron uptake requiring IroN and TonB conferred a fitness advantage during growth in the inflamed intestine. However, the fitness advantage conferred by ferrous iron uptake mechanisms was independent of inflammation and was only apparent in models where the normal microbiota composition had been disrupted by antibiotic treatment.

Mechanical nociceptive thresholds of dorsal laminae in horses after local anaesthesia of the palmar digital nerves or dorsal branches of the digital nerve

We examined the hypothesis that the palmar digital nerves (PDNs), but not the dorsal branches (DBs) of the digital nerves, innervate the sensitive dorsal laminae of the equine foot by evaluating the effects of perineural anaesthesia of the PDNs and DBs separately on pain sensation evoked via mechanical stimulation of the dorsal laminae and other regions of the equine foot. Six clinically normal mares were used in a crossover design. A portable dynamometer was used to evaluate mechanical nociceptive thresholds at different points on the dorsal laminae, bulbs of the heel, coronary band and sole before and after the horses underwent perineural injection of PDNs or DBs with a local anaesthetic solution (treated group) or an isotonic saline solution (control group). Cornified tissue was removed from the sole and the dorsal aspect of the hoof wall before evaluations of mechanical nociceptive thresholds. Anaesthetising PDNs distal to the DBs increased mechanical nociceptive thresholds compared to baseline values (P <0.001) at sites assessed in the dorsal laminae, sole, and the bulbs of the heels. Anaesthetising DBs increased mechanical nociceptive thresholds compared to baseline values (P <0.01) only at sites assessed at the most proximal aspect of the foot (i.e., coronary band sites). In conclusion, PDNs, not DBs, are primarily responsible for pain signal transmission evoked by pressure in the dorsal laminae of the foot of clinically normal horses.