Antibacterial effects of some Cameroonian medicinal plants against common pathogenic bacteria

Abstract

We screened forty crude extracts of twenty Cameroonian medicinal plants commonly used to treat bacterial infections for broad spectrum antibacterial activity, as a more affordable alternative against resistant organisms. The extracts were screened on common pathogenic gram negative and gram positive bacteria initially by the disc diffusion method followed by the tube dilution method. Using discs containing 30µg of extract, Escherichia coli showed sensitivity to 23 extracts with diameter of zone of inhibition ranging from 7 -19mm, fifteen of which were up to or > 10mm. Pseudomonas aeruginosa was sensitive to 11 extracts, whereas Salmonella typhimurium and Staphylococcus aureus were not sensitive to any of the extracts. Based on the zones of inhibition the activity of the extracts were equivalent to 30 to 138 % efficacy of the standard antibiotic discs. The lowest Minimum Inhibitory Concentration (MIC) recorded was 2 mg/ml for Euphorbia hirta against S. aureus and P. aeruginosa and the lowest Minimum Bactericidal Concentration (MBC) was 6 mg/ml for six extracts from Ageratum conyzoides, Aframomum citratum, Euphorbia hirta, Momordica charantia, Mangifera indica and Khaya senegalensis against three bacterial species. Three extracts had broad spectrum bacteriostatic activity (MICs ≤ 4 mg/ml) while in terms of MBCs none of the extracts showed broad spectrum bactericidal activity. We conclude that most of the tested plants used as traditional antibacterials have a bacteriostatic effect on gram-negative pathogenic bacteria.

In vitro anti-Helicobacter pylori activity of extracts of selected medicinal plants from North West Cameroon

“…However, extracts of Emilia coccinea, Eryngium foetidium, Aulatandra kamerunensis, Tapeinachilus ananassae, Euphorbia hirta, Acanthus montanus and Scleria verrucosa were weakly active against the isolates. Although our results showed lower activities of these extracts relative to previous findings (Nkuo-Akenji et Akinyemi et al, 2005;Ngemenya et al, 2006), which reported potent activity of most of the extract of these plants against other gram-negative and -positive bacteria, they however corroborate their reports. This variation may be due to the dose of extracts used in the different studies, the solvent used for extraction, the method of bioassay employed, the age of the plant, and the plant parts used.…”

“…To determine the MBC, 0.2 mL of the contents of the MIC tubes were serially diluted 10-fold in 0.9% physiological saline (Ngemenya et al, 2006). A loop full was taken from each tube and inoculated onto BHI agar plates.…”

“…Medicinal plants such as Xanthum brasilicum, Thymus copticum and Plumbago zeylanica have shown promising anti-Helicobacter pylori activities (Stamatis et al, 2003;Nariman et al, 2004;Wang and Huang, 2005;Mahady et al, 2005). Previous studies have reported high antimicrobial activity of methanolic leaf extracts of Ageratum conyzoides (Compositae) and Euphorbia hirta (Euphorbiaceae) on selected gram-negative and -positive organisms (Ogbeche et al, 1997;Akinyemi et al, 2005;Ngemenya et al, 2006). Emilia coccinea (Asteraceae), used in Cameroon to treat gastrointestinal disorders has been shown to demonstrate significant anti-Salmonella activity at low doses (Nkuo-Akenji et al, 2001).…”

Inhibitory properties of selected South African medicinal plants against Mycobacterium tuberculosis

“…However, the weak activity demonstrated by these extracts in vitro to the organism, does not necessarily imply that they would demonstrate weak activities in vivo. As with some drugs, some of these plant maybe more potent in vivo due to metabolic transformation of their components into highly active intermediates (Ngemenya et al, 2006). Such results provide evidence that these plants might be potential sources of new antibacterial agents even against some resistant strains.…”

In vitro pharmacological evaluation of three Barleria species

“…Weak activities observed in vitro however should not be interpreted to mean that the extracts would give similar activity in vivo. Some of these plant extracts, as with some drugs, may be more potent in vivo due to metabolic transformation of their components into highly active intermediates or their interaction with the immune system (Garcia et al, 2003;Ngemenya et al, 2006). Table 3 shows the anti-inflammatory activity of the various extracts in both COX-1 and COX-2 assays.…”