ANTIBIOTIC treatment is a well-known risk factor for the development of Salmonella and Clostridium difficile infections. This effect has been ascribed to antibiotic-induced alterations in the gut microbiota. But the underlying mechanisms were not understood until now. In a recent study involving a murine model, researchers in California showed that antibiotic-induced alterations in gut carbohydrates promote the expansion of these enteric pathogens.
To understand the growth factors for Salmonella within the gut, the researchers assessed gene expression by Salmonella typhimurium in germ-free mice and in mice colonised with a single Bacteroides (a genus of rod-shaped gram-negative bacteria) species. This work, along with experiments involving mutant S. typhimurium strains, showed that the presence of the carbohydrates fucose and sialic acid strongly influenced the growth of this bacterium.
Similar experiments involving C. difficile showed that increased sialic acid levels within the gut lumen promoted growth. Subsequent studies in conventional mice revealed that antibiotic exposure can markedly increase gut sialic acid levels.
Wild-type S. typhimurium and C. difficile showed growth expansion in the gut of antibiotic-treated conventional mice, with decreased growth of mutant strains of these organisms that lacked the ability to metabolise sialic acid (both S. typhimurium and C. difficile) or fucose (S. typhimurium only).
Experts believe that this work could lead to the development of new preventive strategies.
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