Antimicrobial Activity ofCroton macrostachyusStem Bark Extracts against Several Human Pathogenic Bacteria

Abstract

In Kenya, leaves and roots fromCroton macrostachyusare used as a traditional medicine for infectious diseases such as typhoid and measles, but reports on possible antimicrobial activity of stem bark do not exist. In this study, the antibacterial and antifungal effects of methanol, ethyl acetate and butanol extracts, and purified lupeol ofC. macrostachyusstem bark were determined against important human gram-negative pathogensEscherichia coli,Salmonella typhi,Klebsiella pneumoniae, andEnterobacter aerogenes, gram-positiveListeria monocytogenes,and a fungusCandida albicans. The most promising broad scale antimicrobial activity against all the studied pathogens was shown by the ethyl acetate extract. The ethyl acetate extract induced the zone of inhibition between10.1±0.6 mm and16.0±1.2 mm againstS. typhi,E. coli,K. pneumoniae,E. aerogenes,andL. monocytogeneswith weaker antimicrobial activity againstC. albicans(zone of inhibition:5.6±1.0 mm). The antibiotic controls (amoxicillin, ciprofloxacin, ampicillin, benzylpenicillin, clotrimazole, and cefotaxime) showed antimicrobial activity with zones of inhibition within13.4±0.7–22.1±0.9 mm. The ethyl acetate extract had MIC in the range of 125–250 mg/mL against all the studied bacteria and againstC. albicansMIC was 500 mg/mL. The present results give scientific evidence and support the traditional use ofC. macrostachyusstem bark as a source for antimicrobials. We show thatC. macrostachyusstem bark lupeol is a promising antimicrobial agent against several important human pathogens.