Introduction and objective:
Antimicrobial resistance, which is considered one of the most important problems of the 21 st century, brings many problems with it, such as increasing mortality rates and treatment costs. Difficulties in the treatment of infections caused by resistant microorganisms have led to the search and need for new antimicrobials or new molecules that interact synergistically with antimicrobials. The aim of this study is to investigate whether various flavonoids have synergistic effects with some antibiotics.

Material and methods:
During this study, standard bacterial strains Escherichia coli ATCC 25922, Klebsiella pneumoniae ATCC 700603, Pseudomonas aeruginosa ATCC 9027, Staphylococcus aureus ATCC 29213 and Staphylococcus aureus ATCC 43300 were used. Minimal inhibitory concentrations of all antibiotics and flavonoids were found by the broth microdilution method. Interactions between antibiotics and flavonoids were then determined by using the checkerboard method. Interactions between antibiotics and flavonoids were evaluated according to the FIC index (ΣFIC) results.

Results:
According to the results of the microdilution test, the bacterial strains used in this study (except for MRSA) were generally sensitive to antibiotics. Interaction study results showed promising results regarding the synergistic interactions of antibiotics with flavonoids. Epigallocatechin gallate and luteolin especially showed synergistic interaction with antibiotics in many microorganisms. It was found that myricetin showed synergistic interaction only with levofloxacin. Likewise, it was detected that apigenin had limited synergistic interaction with antibiotics.

Conclusions:
The obtained results highlight that flavonoids may be a useful tool in overcoming antibiotic resistance.