Propolis is a resinous plant material collected by bees to defend their colony. Unlike temperate propolis which is well studied, tropical propolis, particularly from Eastern Africa, remains largely uncharacterized. In this study, the antibacterial and antioxidant activities of Ugandan propolis were evaluated in relation to three bee-keeping agro-ecological zones of the country. Duplicate propolis samples from each agro-ecological zone were extracted by cold maceration in 70% ethanol. Antibacterial assays were conducted in triplicate on reconstituted freeze-dried extracts using two Gram-positive (S. aureus and S. pneumoniae) and two Gram-negative (E. coli and P. aeruginosa) bacteria within a concentration range of ~1.6 to 100 mg/ml. Antioxidant assays were conducted spectrophotometrically on the basis of DCPIP reduction with the resulting decrease in absorbance at 605 nm wavelength. All extracts showed antibacterial activity against S. aureus with MICs ranging from 2.8 to 200 mg/ml, but P. aeruginosa displayed susceptibility only for samples from western highlands (MIC = 9.5 mg/ml). Of the Gram-negatives, E. coli was the more susceptible organism (MICs 5.7-31.5 mg/ml), but S. pneumoniae was susceptible only to samples from mid northern and Lake Victoria crescent (MIC 34.6 mg/ml). Samples from mid northern region exhibited the highest antioxidant activity (mean ± SD activity equivalent to 20.4±4.3 µg of ascorbic acid per mg of extract), while those from Western highlands exhibited the lowest (mean ± SD activity equivalent to 8.9 ± 2.5 µg of ascorbic acid per mg of extract). The antibacterial and antioxidant activities of propolis varied within and between the agro-ecological zones, but the latter variations were generally more pronounced. Taken together, these results highlight the potential of Ugandan propolis as an antioxidant and antibacterial agent. Strategic selection of hive localities in zones that offer the best output in propolis should be a priority for bee-farmers.
Keywords: Propolis, agro-ecological zones, DCPIP, antibacterial, antioxidant, ascorbic acid, Apis mellifera