Effects of short-chain fatty acids on in vitro bacterial growth of Bacteroides fragilis and Escherichia coli

Short-chain fatty acids (SCFA) are produced in the large bowel of nonrumina nt mammals by bacterial anaerobic fermentation. The aim of the present stud y was to investigate the effects of SCFA on the in vitro growth of Bacteroi des fragilis and Escherichia coli. B. fragilis and E. coli isolated from fr esh human clinical samples and a reference strain for each species were inc ubated in a meat infusion broth with increasing amounts of SCFA and grown u nder anaerobic conditions at a temperature of 37 degrees C. Bacterial growt h was estimated by spectrophotometry. Rate of growth was calculated from th e logarithmic growth phase. SCFA, in concentrations normally found in the h uman colon, had a significant (p<0.01) inhibitory effect of the in vitro gr owth rate for E. coli, while they were without effect on the in vitro growt h rate of B. fragilis. It may be concluded that under in vitro conditions S CFA had growth-inhibitory effects on E. coli, while they had no effect on B . fragilis.