A medicament useful in the treatment of affections of the gastro-intestinal tract is prepared by culturing separately, on milk containing gastropyloric mucin of the pig, lysine, arginine and histidine, Lactobacillus acidophilus and non-pathogenic Escherichia coli, and either lyophilizing and then mixing the cultures, or first mixing the cultures, keeping the mixture until it is free from histamine, for example for between 12 and 24 hours, and finally lyophilizing. Medicaments containing 50-150 mg. lyophilized culture of Lactobacillus acidophilus and 50-150 mg. of an equal mixture of the lyophilized cultures of two strains of Escherichia coli together with 20-50 mg. of a lyophilized culture of Bifidibacterium bifidus and (unspecified) amounts of streptogenin in the form of an enzymatic autolysate of fish liver or casein and of other factors, may be bound up in a gelatine capsule; when the enzymatic autolysate is a hygroscopic powder, it is presented separately.  The Lactobacillus acidophilus is cultivated in a medium consisting of 950 ml. sterilized skimmed milk, 50 ml. of a 1% aqueous solution of pig's gastro pyloric mucin (containing 1-2.5% of solids) which is obtained by subjecting a mixture of red mucous and pyloric antrum of the pig to extraction with an aqueous solution of caustic soda, 0.5 gram each of lysine, arginine and histidine, 5 micrograms of crystalline Vitamin B12 and minor amounts of specified antibiotics.  When it has acquired resistance to antibiotics, the ferment is seeded on a similar culture medium containing no antibiotic; before the seeding, the culture medium is sterilized by treating twice at 100 DEG C. with an interval of 24 hours between heating periods.  After seeding, the medium is incubated at 41 DEG C. until a homogeneous curdled product is obtained, which takes about 24 hours.  The curd may then be directly frozen, for example at -60 DEG C., and lyophilized.  Before freezing the lactic acidity may be neutralized to pH 6.5 with trisodium phosphate solution. Non-pathogenic strains of Escherichia coli which acidify lactose-containing media in less than 24 hours, give indole, do not grow on a disclosed medium containing citrate, are free from haemolysins active against red corpuscles and show the greatest resistance to common antibiotics, are preferred.  Two different strains of Escherichia coli are separately cultivated in successive mixtures of the above-described culture medium with decreasing amounts of peptone-containing water consisting of 15 grams peptone, 5 grams sodium chloride and 1 gram of lactose per litre.ALSO:A medicament useful in the treatment of affections of the gastro-intestinal tract is prepared by culturing separately, on milk containing gastropyloric mucin of the pig, lysine, arginine and histidine, Lacto bacillus acidophilus and non-pathogenic Escherichia coli, and either lyophilising and then mixing the cultures, of first mixing the cultures, keeping the mixture until it is free from histamine, for example for between 12 and 24 hours, and finally lyophilising.  Medicaments containing 50-150 mg. lyophilised culture of Lactobacillus acidophilus and 50-150mg. of an equal mixture of the lyophilised cultures of two strains of Escherichia coli together with 20-50mg. of a lyophilised culture of Bifidibacterium bifidus and (unspecified) amounts of strepogenin in the form of an enzymatic autolysate of fish liver or casein and of other farters may be bound up in a gelatine capsule; when the enzymatic autolysate is hygroscopic powder, it is presented separately.  The medicament may be administered to infants and adults in the treatment of gastro-intestinal infections in general, may receiving particular mention, notably gastroenteritis and colitis, and to pigs, immediately they are born, to reduce their rate of mortality.