In vitro antimicrobial and resistance-modifying activities of aqueous crude khat extracts against oral microorganisms.
OBJECTIVE
To assess antimicrobial activities of aqueous crude khat (Catha edulis) extracts against a panel of oral microorganisms and to test their ability to modify bacterial resistance to tetracycline and penicillin in vitro.


METHODS
Lyophilized aqueous extracts were prepared from three khat cultivars. The agar dilution method of the NCCLS was used to test the extracts, at concentrations of 20-1.25 mg/ml, against 33 oral strains. MIC was defined as the lowest concentration at which there was no visible growth. Slight growth was defined as marked growth reduction (MGR). The E-test was used to determine the MICs of tetracycline and penicillin-G for three resistant strains in absence and presence of a sub-MIC of the khat extracts (5mg/ml).


RESULTS
Eighteen strains (55%) were sensitive to the extracts (MICs 5-20 mg/ml). Most of these were periodontal pathogens with Porphyromonas gingivalis and Tannerella forsythensis being the most susceptible (MIC 5-10mg/ml). Veillonella parvula, Actinomyces israelii and some streptococci were not sensitive. Except for Lactobacillus acidophilus that showed MGR at 1mg/ml, cariogenic species were neither sensitive. The extracts were active against Streptococcus pyogenes (MIC 10-20 mg/ml) but not against Candida albicans and Staphylococcus aureus. The presence of the khat extracts at a sub-MIC resulted in a 2-4-fold potentiation of the tested antibiotics against the resistant strains.


CONCLUSIONS
Khat has water-soluble constituents possessing selective antibacterial activity against oral bacteria. There is preliminary evidence for presence of an antibiotic resistance-modifying component. Further investigation is needed to identify the active components and assess their clinical relevance.
Al-hebshi
Nezar
N
Laboratory of Oral Microbiology, Department of Oral Sciences--Oral Microbiology, Faculty of Dentistry, University of Bergen, Armauer Hansens Hus, N-5021 Bergen, Norway. Nezar.Al-hebshi@student.uib.no
Al-haroni
Mohammed
M
Skaug
Nils
N
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001419:Bacteria / Q000187:drug effects*; D002176:Candida albicans / Q000187:drug effects; D029754:Catha / Q000737:chemistry*; D004347:Drug Interactions; D024881:Drug Resistance, Bacterial / Q000187:drug effects; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods; D009055:Mouth / Q000187:drug effects / Q000382:microbiology*; D010400:Penicillin G / Q000494:pharmacology*; D010936:Plant Extracts / Q000494:pharmacology; D013752:Tetracycline / Q000494:pharmacology*
D000900:Anti-Bacterial Agents; D010936:Plant Extracts; D013752:Tetracycline; D010400:Penicillin G