Affiliation(s)
1. Croatian Institute for Experimental and Translation Oncology (CIETO), Koledinečka 03, Zagreb 10040, Croatia
2. Institutes of Biomedical Sciences, Medical Faculty of Maribor, Taborska 8, Maribor 2000, Slovenia
3. Retired, Glavarjeva 19, Ljubljana 1000, Slovenia
4. Research and Developement, Medex D.o.o., Linhartova 049a, Ljubljana 1000, Slovenia
5. Institutes of Microbiology and Immunology, Medical Faculty, Zaloška 4, Ljubljana 1105, Slovenia
ABSTRACT
Propolis is a resinous
natural product, produced by bees (Apis mellifera), from vegetable parts
and plant secretions. Propolis’ samples A, B, C and D were extracted with
phosphate buffer saline (PBS) or with 70% EtOH at pH
values 8.0, 7.2 and 6.4 followed by: (1) reverse-phase
high-performance liquid chromatography (RP-HPLC) on Purospher® Star RP-18 column, the quantity of
caffeic acid, chrysin, pinocembrin and galangin was determined; (2) determination of total flavonoids in both
extracts; (3) antimicrobial
tests of both extracts against (a) Gram-positive bacteria:
methicillin-resistant Staphylococcus aureus (MRSA), St. aureus, Streptococcus pyogenes, Str. agalactiae, (b) Gram-negative bacteria: Escherichia coli, Pseudomonas
aeruginosa, Proteus mirabilis, Acinetobacter baumanii and (c)
yeast: Candida albicans. The antimicrobial activity of propolis’ PBS extracts
against Gram-positive bacteria shows the lowest minimal inhibitory concentration (MIC, mg/mL) at pH 8.0 in
sample C, followed by A, B and D. In sample C, MICs at pH 8.0 were 0.007 (Str. agalactiae),
0.015 (MRSA), 0.015 (Str. pyogenes) and 0.007 (St. aureus). The polyphenol
content of sample C is: flavonoid content
5.47 ± 0.62
mg/mL, caffeic acid 1.33 ± 0.92 mg/mL, chrysin
41.02 ± 4.22 µg/mL, pinocembrin 2.93 ± 0.33 mg/mL and galangin 41.87 ± 4.23 mg/mL. PBS extracts against Gram-negative bacteria show the
lowest MIC (mg/mL) at pH 8.0 in sample D, followed by B, C and A. In sample D, MICs at pH 8.0 were
0.003 (Acin. baumanii, Pr. mirabilis, Ps. aeruginosa)
and 0.007 (E. coli). Polyphenol content of
sample D is: flavonoids 8.28 ± 0.92 mg/mL, caffeic acid
3.56 ± 0.32 mg/mL, chrysin 677.42 ± 68.42 μg/mL, pinocembrin 146.49 ± 13.89 mg/mL and galangin 59.81 ± 5.86 mg/mL. The strongest anti C. albicans activity, with the lowest MIC (mg/mL), at pH 8.0 was in the sample C,
followed by samples D, A and B. In sample C, the MIC at pH 8.0 is 0.001 (PBS
extract). The antimicrobial
activities of selected propolis samples correlate with their polyphenol
content, more precisely, flavonoid, caffeic acid, chrysin, pinocembrin and
galangin content.
KEYWORDS
Propolis, pH, phosphate
buffer saline extract, 70% EtOH extract, antimicrobial activity.
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