Antimicrobial action of propolis extracts against staphylococci

Abstract

One Health is a worldwide strategy of healthcare for humans, animals, and the environment. Antimicrobial resistance is a serious global problem, recently recognised by the World Health Organization. Prudent, responsible use of antimicrobials should be a concern for both human and veterinary doctors. Concerning animal health and its repercussion in human health, antimicrobials and disinfectants have been widely used for the control of mastitis. This practice induces a selective pressure for resistant bacterial strains, which is deleterious for public health associated with milk consumption. Antimicrobial resistance genes have been detected in pathogens associated to small ruminants’ mastitis. These genes may be transferred to the indigenous microbiota of humans. The presence of disinfectant resistance genes has also been reported in staphylococci from both ovine and caprine milk. Propolis is a resinous substance produced by honeybees using different types of plants. It is used to seals holes and cracks in the beehive, contributes to an aseptic internal environment, maintains the hive’s internal temperature, and prevents predators from entering the beehive. Propolis has been used as a natural medicine for its antiseptic, antimicrobial, antioxidant, anti-inflammatory, and other immunomodulatory properties. The aim of the present study was to investigate the in vitro activity of propolis ethanol extracts (PEE) against staphylococci isolated from mastitic milk of sheep and goats. Antimicrobial susceptibility was assessed for 16 antimicrobials (ampicillin, gentamicin, lincomycin, trimethoprim/sulfamethoxazole, penicillin, streptomycin, tetracycline, cloxacillin, neomycin, cefazolin, cefoperazone, cephalexin, amoxicillin+clavulanic acid, oxacillin, ceftriaxone, and ciprofloxacin) by the disk diffusion method. Ten PEE from propolis samples collected both in Portugal (three brown), and Brazil (one green, two red, and seven brown) were evaluated for their antimicrobial action against 146 staphylococci: 35 S. aureus, and 104 coagulase-negative staphylococci isolates, together with seven reference strains. Antimicrobial activity of PEE was assessed on polystyrene flat- bottomed microtiter plates in triplicate by the microdilutions methodology for concentrations between 0.05 and 214 mg/mL. All staphylococci isolates revealed susceptibility to all but one of the studied PEE. Minimal bactericidal concentration for most isolates was 3.34 mg/mL. According to our results, propolis may be an important alternative to the use of antimicrobials, with remarkable advantages for public health.