Which bacterium uses mucosal invasion as a mechanism of disease in the GI tract?

• A. Escherichia coli
• B. Salmonella species
• C. Campylobacter jejuni
• D. Vibrio parahaemolyticus

Answer: (B)

Mucosal invasion of the intestinal lining is the mechanism in play. Salmonella species invade the gut mucosa by crossing the epithelial barrier, notably through M cells in Peyer’s patches, and then multiply within macrophages in the lamina propria. This invasion triggers a robust inflammatory response with neutrophil recruitment, producing an inflammatory diarrhea that can be feverish and sometimes bloody. The invasive strategy also explains occasional systemic spread via infected macrophages. By contrast, the other organisms more often cause disease through toxins or adherence without deep invasion: many E. coli pathotypes cause secretory or toxin-mediated diarrhea, Campylobacter can irritate and damage mucosa but is not defined primarily by invasion, and Vibrio parahaemolyticus mainly drives symptoms through enterotoxins and cytotoxins rather than mucosal invasion.