Influence of Lactic Acid Fermentation on Enteropathogenic Bacteria. Growth Inhibition in Cereal Gruels and in Human Intestine

Sammanfattning: Togwa, a lactic-fermented cereal gruel, is widely consumed in Tanzania as a soft drink or used as a complementary food for young children. Studies were conducted to evaluate the potential of togwa to inhibit growth of common enteropathogenic bacteria and heat-labile (LT) enterotoxin production. Single strains of enteropathogenic bacteria were inoculated into the gruel at the beginning of the fermentation process initiated using three different starters: 1. starter culture (SC) prepared by inoculum recycling of a previous togwa batch, 2. germinated sorghum flour, power flour, (PF) or 3. a combination of SC and PF. The number of viable cells (CFU/mL) for each enteropathogenic bacteria was then measured from sub-samples collected at intervals during the fermentation process. The presence of LT enterotoxin in togwa was also determined from the sub-samples using the Chinese hamster ovary cell test. In a community study, the prevalence of enteropathogenic bacteria in rectal faecal swabs from healthy children was measured before, during and after consumption of togwa. Children consuming unfermented gruel were used as controls.

At a paediatric ward, young children with diarrhoea were given togwa or unfermented cereal gruel. The influence of togwa consumption on recovery of intestinal mucosal damage was measured using the lactulose:mannitol (L/M ratio) permeability test. Age matched healthy children from a local maternal and child health clinic were used as controls.

Results showed that combining a daily recycled SC and PF resulted in a faster decrease in pH and growth inhibition of enteropathogenic bacteria (p < 0.05) than using either of the starters alone. The growth inhibition rate was correlated with pH development (r = 0.71; p < 0.01). Production of LT enterotoxin was inhibited in togwa but not in control gruels. Compared with baseline, the prevalence of pathogenic faecal bacteria was reduced during the study period in children consuming togwa (p < 0.001) but not in the control group. The protection from recontamination was carried over up to fourteen days after consumption of togwa had stopped. Children with diarrhoea had a higher intestinal permeability (L/M ratio = 0.85) at admission to hospital compared with the control healthy children (L/M ratio = 0.14, p < 0.001). Children in the togwa group showed a faster drop in L/M ratio between admission day and day three compared with the other two study groups (p < 0.04). The L/M ratio on day three was also lower (p < 0.01) than in the other two groups.

In conclusion, togwa prepared using a combination of a daily recycled SC with PF results in accelerated increase in acidity which is a key factor to the inhibitory effect to common enteropathogenic bacteria. This make such togwa to have a potential in inhibiting the growth of common enteropathogenic bacteria and production of LT enterotoxins. A regular consumption of such togwa could protect young children from being exposed to potential diarrhoea causing bacteria or being colonized with them. The recovery of intestinal mucosa damaged during diarrhoea was faster in children consuming togwa.