In vitro susceptibility testing of Yersinia species to eight plant extracts and three natural antimicrobial agents
The antimicrobial effects of the ethanolic and aqueous extracts of the leaves of Cymbopogon citratus (DC) Stapf, Acalypha hispida Forsk, Vernonia amygdalina Del, Occimum gratissimum L., Sida acuta Burm, F., Coffea arabica L., seeds of Carica papaya L., fruit juice of Citrus aurantifolia (Christim) Swingle, wild honey, processed honey (Laser brand) and processed coffee (Nescafe) on Yersinia pesudotuberculosis, Yersinia enterocolitica 0:3, Yersinia enterocolitica 0:8, Yersinia Kristensenii 0:11, 23, Yersinia intermidia 0:52, 53, and Yersinia intermidia-like bacteria were evaluated. In this study, only processed honey did not inhibit the test organisms, while other extracts investigated show varying zones of inhibition. The zones of inhibition obtained from the aqueous extract ranged from 6.0 mm for V. amygdalina Del against Y. enterocolitica 0:03 to 17.7 mm for Citrus aurantifolia (christim) Swingle against Y. pesudotuberculosis , while the zones of inhibition obtained for ethanolic extract ranged from 6.6 mm for V. amygdalina Del against Y. enterocolitica. 0:3 to 17.6 mm for processed coffee against Y. pseudotuberculosis. The minimum inhibitory concentration (MIC) of the various antimicrobials ranged from 0.0034 ìg/ml for Y. enterocolitica 0:3 to 0.00155 µg/ml for Y. intermedia 0.52, 53, using dilution techniques. The MIC compares with that of commercial antibiotics and therefore suggest that these extracts could be used in the effective management of yersiniosis, in this era of bacterial multiple drug resistance to commonly used antibiotics. However, further studies to determine the shelf life, appropriate dosages and/or whether there are any contraindications for those who may use these extracts as medication is recommended.
Key words: Plant extracts, natural antimicrobial agents, anti-Yersinia species agent.