In vitro activity of propolis: Synergism in combination with antibiotics against Staphylococcus spp.

Mastitis causes inflammation of the mammary gland and physical, chemical and bacteriological alterations in milk. The control of this disease deserves special attention within health programs of the dairy cattle industry. The aim of the present study was to assess the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of a commercial product (gentamicin + amoxicillin) indicated for the treatment of mastitis, propolis,and their association against Staphylococcus spp. In total, 70 samples of Staphylococcus spp. isolated from cases of subclinical mastitis, were used in the present study. The bacterial isolates were tested against the commercially available association of gentamicin and amoxicillin, as well as commercially available propolis. Muller Hinton (MH) micro-broth dilution was used in the present study. The presence of phenolic compounds and flavonoids was confirmed in the propolis used. The MIC values ​​found for gentamicin and amoxicillin were 0.2258 g/ml and 0.8469 mg/ml, respectively. The MBC values found for gentamicin and amoxicillin were 1.7793 and 6.6722 mg/ml, respectively. The mean MBC values of amoxicillin and gentamicin in synergism with propolis were 0.1384 g/ml and 0.5235 mg/ml, respectively. Analysis of propolis showed the presence of derivatives of the following acids: caffeic; cinnamic; p-coumaric; ferulic and 3,4-dihydroxybenzoic. The results of the present study showed that gentamicin and amoxicillin, associated with propolis, exhibit synergistic activity that could reduce the selection of resistant microorganisms. The synergistic effect of propolis is probably due to the presence of cinnamic acid derivatives.