Propolis antibacterial and antioxidant synergisms with gentamicin and honey

Abstract

Aims: Assess the antibacterial and antioxidant effects of ethanol extracts of Portuguese propolis samples when combined with gentamicin, a widely used aminoglycoside antibiotic, or with honey, collected from the same apiary as propolis. Methods and Results:Using the agar dilution method and DPPH free radical scavenging assay, antimicrobial and antioxidant synergistic effects between propolis and gentamicin or honey were assessed. Synergism between propolis and gentamicin was observed for all the tested extracts and against all the indicator bacteria, with particular interest against the Methicillin-Resistant Staphylococcus aureus (MRSA) with a threefold decrease of the gentamicin MIC if mixed with 25 µg ml −1 propolis.Likely to propolis and gentamicin, mixtures of sub-MIC concentrations of propolis and honey enhanced the antibacterial action of each individual natural product against the majority of the strains. However, propolis antioxidant capacity decreased along with higher honey content in the mixture.Conclusions: Propolis has a strong synergistic effect when combined with gentamicin, allowing the reduction of the therapeutic dose of this drug. Propolis and honey mixtures also display a stronger antibacterial effect than the activity exhibited by each sample when tested individually, whereas the high antioxidant capacity of propolis seems to be not affected when in combination with honey. Significance and Impact of Study: When mixed with honey, propolis antioxidant potential is maintained, or just slightly reduced up to 1:1 dilution, and show synergistic antibacterial effects, allowing to optimize the use of this usually scarce natural resource. Also, considering the antibiotic resistance problem, natural beehive products, alone or in the mixture, are promising alternatives to retard the outbreak of microbial resistance.

Mixing Propolis from Different Apiaries and Harvesting Years: Towards Propolis Standardization?

“…A curious observation from all of these results is that P14.EE, one of the extracts with the lowest TPC and TFC ( Table 1 ) and antioxidant capacity ( Table 2 ) was the one with the highest antibacterial activity ( Table 3 ) but did not have a high anti-yeast activity ( Table 4 ), where typically P15.EE and P15.EE-mixtures excel. This seems to suggest that propolis mode of action against bacteria is not as tightly related to its level of polyphenols and flavonoids contents per se, but possibly is related to certain combinations of compounds or specific synergisms, as has been reported [ 43 ].…”

Investigating Possible Synergism in the Antioxidant and Antibacterial Actions of Honey and Propolis from the Greek Island of Samothrace through Their Combined Application

“…According to previous research [ 31 , 62 ], the combination of different honeys with propolis extracts from Spain and Poland resulted in the degradation of the sensory properties of the mixtures, but also showed a noteworthy increase in their polyphenolic content and antioxidant activity, with the antimicrobial activity also increasing in some mixtures. In another recent study, propolis and honey mixtures were also found to display a stronger antibacterial effect than the activity exhibited by each individual sample, whereas the high antioxidant capacity of propolis was not affected when used in parallel with honey [ 30 ]. In another study which concurrently employed starch and honey [ 63 ], the addition of starch to five different honey samples increased their antimicrobial properties against Pseudomonas aeruginosa , an opportunistic and pathogenic bacterium well-known for its multidrug resistance and association with some serious hospital-acquired infections [ 64 ].…”

“…However, research on these two substances has until now tended to focus on them individually and independently of each other. Nevertheless, there are still some promising data on the synergistic biological effects of the combined use of these two hive products, either alone or together with other bioactive compounds (e.g., antibiotics) [ 29 , 30 , 31 ]. Such a combined action could further increase their functional properties and also lower their minimum effective concentrations.…”

Portuguese Propolis Antitumoral Activity in Melanoma Involves ROS Production and Induction of Apoptosis

“…In particular, the sample collected in Montalegre (north of Portugal) exhibited a scavenging activity effect with an EC 50 value of 10 µg/mL. According to Freitas et al [ 62 ], G18.EE has an EC 50 value of 12.40 ± 0.43 µg/mL. This value was calculated in 2018, the sample’s harvest year.…”

“…Fractionation of propolis from Gerês was performed as previously described by Ana Freitas [ 62 ]. Briefly, 4 g of G18.EE was dissolved in 20 mL of absolute ethanol and, after becoming a homogenous solution, 200 mL of purified water were added.…”