This study was carried out to isolate and identify Escherichia coli from diarrheic fecal samples of calves and piglets in Ibadan, Nigeria and to determine the antimicrobial activities of some medicinal plants on these Escherichia coli isolates as an agent of diarrhea in livestock. It also aimed at extracting the therapeutic component of the ethnomedicinal plants using different solvents and determining the efficacy of the plants extracts on E.coli by disc diffusion and minimal inhibitory concentration (MIC) methods. E. coli strains showed a high frequency of single or multiple drug resistance (MDR) to ≥3 of the antimicrobial agents tested (3 to 6 antibiotics). The bacteria were found to be resistant to ampicillin, nalidixic acid, nitrofurantoin, co-trimoxazole, streptomycin and tetracycline. Chloroform, methanol and warm water extracts of the leaves of Ageratum conyzoides, Adansonia digitata, Annona muricata, Bryophyllum pinnatum Kuiz, Cassia sieberiana, and Ocimum gratissimum traditionally employed for the treatment of gastrointestinal infections were prepared and evaluated for its antimicrobial activities. Extracts of Adansonia digitata, Bryophyllum pinnatum, Cassia sieberiana and Ricinus communis did not inhibit E. coli at the various concentrations. Only methanol extracts of Ageratum conyzoides, Annona muricata and Ocimum gratissimum showed some degree of inhibition which varies with the E. coli strain tested. The methanol extracts of the plant parts were more potent than the chloroform and water extracts which showed no activity against the test organisms. Neat (100%) concentration of methanol preparation inhibited the growth of Escherichia coli. The minimum inhibitory concentration (MIC) exhibited by Ocimum gratissimum against the E. coli strains was 20,000μg/ml. The presence of these MDR- E. coli strains in these diarrhoeic piglets indicates public health hazard and calls for particular attention and warning signal for the possible occurrence of food borne intoxication. The result suggests that the preparation of these three plants exhibited significant in vitro antimicrobial activity against common gastrointestinal isolates and may be employed for the routine treatment of gastrointestinal infection as an alternative to antibiotics chemotherapy.
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