| Prebiotics are non-digestible substances that provide beneficial physiological effect on the host when consumed, by selectively stimulating the favourable growth or activity of beneficial bacteria such as Lactobacilli. Ocimum gratissimum is a Nigerian leafy vegetable known for its vast bioactive compounds and therapeutic use. This research aimed at identifying the prebiotic compounds present in O. gratissimum ethanolic extract and to observe their roles in the control of colibacillosis in

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... lers; as a natural alternative to antibiotic therapy. Prebiotics present in O. gratissimum were assessed using ethanolic extraction and thin layer chromatography. A 1.5 ml aliquot of 10 6 cfu/ml E. coli O157:H7 isolated from Nono (sour milk) and identified with 16s rDNA sequencing, was used to elicit colibacillosis infection in three weeks old broilers. Ethanolic extract of O. gratissimum (40 g/L) was orally administered, Norfloxacin (15 g/L) was used as the antibiotic control, uninfected broilers were used as healthy control and broilers infected without treatment were used as negative control for the experiment which was monitored over a period of four weeks. Data were analyzed using Tukey test for mean partitioning. Prebiotics present in O. gratissimum were mainly fructooligosaccharides. Administration of the plant prebiotics to the infected birds resulted in appreciable weight gain (P =0.015), decrease in total E. coli count (P =0.006) and increase in total lactic acid bacteria count (P = 0.025) in the caecum. Histopathology examination of the caecal tissues revealed mucosal lipidosis in the caecum, which indicates probably short chain fatty acid production from prebiotic fermentation by beneficial bacteria that inhabit the colon. O. gratissimum prebiotic administration can serve as an antibiotic alternative to control the colibacillosis in broilers, which poultry farmers can be encouraged to adopt to limit the cases of microbial resistances from poultry farms.