Stimulatory and inhibitory effects of green leaf volatiles on "good" (Commensal) and "bad" (Pathogenic) bacteria in the intestine*

The balance between beneficial and pathogenic bacteria in the intestine has a great importance in terms of gut physiology and immunity. The aim of the study was to investigate the stimulatory and inhibitory effects of aldehydes from green leaf volatiles (trans-2-hexenal, cis-3-hexenal, trans-2-nonenal and, trans-2-decenal) on beneficial (Bifidobacterium bifidum, Bifidobacterium longum, Lactobacillus acidophilus and, Lactobacillus casei) and pathogenic bacteria (Fusobacterium nucleatum, Clostridium perfringens, Staphylococcus aureus, Escherichia coli and, Salmonella typhimurium) from the intestine. E. coli, S. typhimurium and, S. aureus, which are facultative anaerobes, were grown using bacterial-specific media in the incubator at 37°C. Other intestinal bacteria, which are strictly anaerob, were grown in anaerobic cabinet at 37°C for 24-48 hours using anaerobic media. Minimal inhibitory concentration (MIC) values of green leaf volatiles on intestinal bacteria were investigated by microdilution method in the range of 3.9, 7.8, 15.6, 31.3, 62.5, 125, 250, 500 and, 1000 μg/ml concentrations. The lowest MIC value of green leaf volatiles determined on intestinal bacteria was 500 μg/mL. It was observed that beneficial gut bacteria were more resistant to green leaf volatiles than pathogens. The growth of B. bifidum was stimulated by trans-2-hexenal and trans-2-decenal at 3.9-250 μg/mL (P<0.05), by cis-3-hexenal at 15.6 and 31.3 μg/mL (P<0.05) and, by trans-2-nonenal at 3.9-500 μg/mL doses (P<0.05). Trans-2-decenal also stimulated moderately growth of L. acidophilus at 31.3 and 62.5 concentrations (P<0.05). Trans-2-hexenal, cis-3-hexenal and, trans-2-nonenal did not exhibit inhibitory effect on beneficial intestinal bacteria except B. longum. Trans-2-decenal was most effective aldehyde on pathogens, with growth-inhibitory effect on C. perfringens, F. nucleatum and, S. aureus at the concentration of 500 μg/ml (P<0.05). Trans-2-decenal also protected beneficial bacteria at the dose that it inhibited pathogen ones. All used compounds inhibited F. nucleatum as one of the agents of colorectal cancer, at 500 μg/ml dose (P<0.05). E.coli and S. typhimurium from pathogens were resistant to all green leaf volatiles while S. aureus was inhibited only by trans-2-decenal at 500 μg/mL dose (P<0.05). In conclusion, it is thought that the used green leaf volatiles might have beneficial effects on gut health by regulating beneficial bacteria and inhibiting pathogenic bacteria. In vitro and in vivo trials investigating the effects of green leaf volatiles on the mixed cultures of intestinal bacteria will contribute to the elucidation of the subject.