IN VITRO INVESTIGATION ON SYNERGISTIC ANTIMICROBIAL EFFECTS OF DAIDZEIN, ROYAL JELLY AND BORIC ACID IN COMBINATION WITH CERTAIN ANTIBIOTICS AGAINST GRAM-POSITIVE AND GRAM-NEGATIVE BACTERIA STRAINS
The prevalence of infections caused by multiple antibiotic resistant microorganisms has
made it important to investigate substances that may have synergistic effects with antibiotics. The aim of
this study is to investigate possible synergistic antimicrobial effects of daidzein (DZ), royal jelly (RJ) and
boric acid (BA) in combination with certain antibiotics against different bacteria strains. Staphylococcus
aureus, Escherichia coli, Klebsiella pneumoniae, Entercoccus faecium, Pseudomononas aeruginosa and as
a control strain, S. aureus ATCC 43300 were used in this study. Daidzein, royal jelly, boric acid, cefuroxime
sodium (Cef), levofloxacin hemihydrate (Levo) and trimethoprim (Tri) MIC values were determined by the
method of macrodilution. In vitro synergy tests were studied using the checkerboard method. The
combination of Levo+BA against bacteria strains S. aureus, E. coli and E. faecium; and the combination of
Tri+BA against S. aureus, E. coli and K. pneumoniae had a significant synergistic interaction (ΣFIC<0.5).
The combinations of Cef+RJ against K. pneumoniae, Levo+RJ against E. coli, and Tri+RJ against S. aureus,
E. coli and K. pneumoniae had also a significant synergistic interaction (ΣFIC<0.5). In addition, the
Levo+DZ combination showed synergistic interaction against E. coli and E. faecium strains. Our study
results showed that the effectiveness of some antibiotics against different bacterial strains can be increased,
especially in combination with BA or RJ.