Antimicrobial activity of Euclea undulata, Euclea divinorum and Diospyros lycioides extracts on multi- drug resistant Streptococcus mutans

Abstract

The antimicrobial activities of three Zimbabwean chewing sticks (Euclea undulata, Euclea divinorum and Diospyros lycioides) on multi-drug resistant (MDR) Streptococcus mutans were determined. Thirty one isolates of S. mutans were obtained from 47 carious teeth and antibiotic sensitivity testing was done using the disc diffusion assay for all isolates. The resistance pattern of each isolate against eight antibiotics was noted. Eight resistance patterns were identified, and 19 isolates showed resistance to at least 4 antibiotics; these were considered MDR. Eight MDR and 2 multi-drug sensitive isolates were then assayed against methanol, acetone, diethyl ether and aqueous extracts of E. undulata, E. divinorum and D. lycioides. The broth macro-dilution assay was used to determine the minimum inhibitory concentration (MIC) of the extracts. All E. divinorum extracts showed no antimicrobial activity. Stem methanol extracts of E. undulata and root and stem methanol extracts of D. lycioides showed anti S. mutans activity. The largest inhibition zones were exhibited by methanol extracts of E. undulata (60 mm) and D. lycioides (54 mm). MICs ranged from 0.385 to 11.22 mg/ml and minimum bactericidal concentration (MBCs) from 0.485 to 20.20 mg/ml. D. lycioides and E. undulata extracts have potential use as anticariogenic agents. Key words: Streptococcus mutans, dental caries, antimicrobial activity, multi-drug resistant