Antagonism against Vibrio cholerae by diffusible substances produced by bacterial components of the human faecal microbiota

Cholera vibrios sometimes survive, probably in low-level silent populations , in the small intestine of chronic carriers or pass through the gastrointe stinal tract of a few individuals without causing diarrhoea or colonisation . To understand these situations, the present study used plate cultures (ex -vivo test) to investigate the frequency of appearance of an inhibitory hal o against Vibrio cholerae produced by faecal specimens from 92 healthy volu nteers (40 females, 52 males) aged 4-61 years. The frequency of inhibitory halo was 20.6% in the whole group. An apparently higher percentage (27.3%) was observed in the age range 20-40 years when compared with the range 4-19 years (10.7%), but not the range 41-61 years (20.0%). Frequency was signif icantly higher in males (30.8%) than females (7.5%). The dominant microbiot a of a volunteer whose faeces produced an inhibitory halo was isolated by p late culture of decimal dilutions in an anaerobic chamber. Potential isolat es of 26 apparently different morphologies were associated with germ-free N IH mice. One week later, the inhibitory test showed an antagonistic halo ar ound the faeces from the associated animals, but not from the axenic mice, Of the 26 bacteria isolated, two (Lactobacillus sp, and Peptostreptococcus sp.) produced a compound antagonistic against V. cholerae in an in-vitro as say. When bi-associated with germ-free mice those strains eliminated the vi brio from the intestinal ecosystem in c, 5 days.