Effects of fermentation products of the commensal bacterium Clostridium ramosum on motility, intracellular pH, and flagellar synthesis of enterohemorrhagic Escherichia coli.

The flagellum and motility are crucial virulence factors for many pathogenic bacteria. In general, pathogens invade and translocate through motility and adhere to specific tissue via flagella. Therefore, the motility and flagella of pathogens are effectual targets for attenuation. Here, we show that the fermentation products of Clostridium ramosum, a commensal intestinal bacterium, decrease the intracellular pH of enterohemorrhagic Escherichia coli (EHEC) and influence its swimming motility. Quantifications of flagellar rotation in individual EHEC cells showed an increase in reversal frequency and a decrease in rotation rate in the presence of C. ramosum fermentation products. Furthermore, the C. ramosum fermentation products affected synthesis of flagellar filaments. The results were reproduced by a combination of organic acids under acidic conditions. Short-chain fatty acids produced by microbes in the gut flora are beneficial for the host, e.g. they prevent infection. Thus, C. ramosum could affect the physiologies of other enteric microbes and host tissues.