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DOI: 10.1055/s-0033-1352323
Antimicrobial activity of Romanian propolis ethanolic extracts against E. coli isolated from bovine mastitis
Escherichia coli, nominated as one of the major bacterial pathogen of bovine mastitis, is also reported for its elevated antimicrobial resistance level [1,2]. The stringent need of research into natural alternatives to antimicrobials is emphasized as well by the current farm animal health and welfare policies [3] and propolis extracts were suggested by several authors for the anti-staphylococcal potency [2,4]. The study was aimed to investigate the antimicrobial activity of ten Romanian propolis samples against E. coli strains (n = 5) isolated from bovine mastitis; these strains were selected based on their resistance pattern: penicillin, streptomycin, tetracycline, novobiocin, neomycin, ampicillin, and amoxicillin-clavulanic acid (antimicrobials commonly used for mastitis treatment and control). As the first screening performed by a disk diffusion method indicated only a moderate activity in case of two propolis samples (with the maximum obtained inhibition diameters of 7 – 10 mm), minimum inhibitory concentrations (MIC) were established using a broth microdilution assay for propolis samples tested alone and with the amoxicillin-clavulanic acid combination. The most intense synergistic effect was noticed for the MIC of 8% v/v in case of propolis sample with the highest concentration of total phenolics (48.11 ± 2.76 mg/g propolis). Based on these in vitro results, Romanian propolis samples can be considered as complex natural antimicrobial products with beneficial effects on maintaining the bovine udder health and productivity when confronted with multiresistant E. coli strains.
Propolis Sample ID |
Total phenolics (mg/g propolis) |
Diameter of inhibition zones (mm) |
MIC (% v/v) |
|
Propolis Sample |
Propolis Sample + AMC |
|||
1 – 2 |
30.61 ± 1.16 |
7 ± 0.5 |
8 |
4 |
3 – 7 |
34.96 ± 9.36 |
10 ± 0.2 |
0.5 |
0.25 |
8 – 9 |
45.6 ± 3.27 |
21 ± 2.4 |
0.125 |
< 0.125 |
10 |
48.11 ± 2.76 |
22 ± 0.5 |
0.125 |
< 0.125 |
(AMC = amoxicillin-clavulanic acid) |
References:
[1] Santana, H.F. et al. (2012) World J Microbiol Biotechnol. 28(2):485 – 91.
[2] Pinto, M.S. et al. (2001) Braz. J. Vet. Res. Anim. Sci. 38(6):278 – 283.
[3] Ivemeyer, S et al. (2011) Proceedings of the international mastitis conference, Wageningen Academic Publishers, 69 – 76.
[4] Rahman, M.M. et al. (2010) Afr. J. Microbiol. Res. 4:1872 – 1878