Studies on multidrug-resistant microorganisms, especially Escherichia coli (E. coli) strains, continue worldwide. In addition to the discovery of new antibiotics, there is also significant research on resistance mechanisms. One such mechanism is the efflux pump, which rapidly expels substances (antibiotics) from the bacterial cell or reduces their concentration. Therefore, the effectiveness of antibiotics can be restored by preventing this mechanism, and studies on potential inhibitors in this direction are ongoing.

In this study, the potential inhibitory effect of acetone extract obtained from Phellinus hartigii (P. hartigii) against drug-resistant E. coli strains was investigated. This was done by using the extract in combination with the antibiotics aztreonam (ATM 30 µg), cefixime (CFM 5 µg), amoxicillin–clavulanate (AMC 30 µg), piperacillin–tazobactam (TZP 36 µg), and ceftriaxone (CRO 30 µg) (Oxoid, UK).

For the first stage of inhibition, the Ethidium Bromide (EtBr) test was used with P. hartigii acetone extract. After observing inhibition according to the test results, antibiotic disks were applied together with the extract, antibiotic, and resistant strains. As a result of this study, it was observed that activities against E. coli#3 strain ATM (MIC 4), E. coli#10 strain ATM (MIC 8), E. coli#7 strain TZP (MIC >16/4), and E. coli#8 strain TZP (MIC >16/4) were restored. Based on these findings, P. hartigii acetone extract may have a potential efflux pump inhibitory effect, but further studies are required to explain this effect more broadly.

Acknowledgement: This study was supported by the Kastamonu University Scientific Research Project
(KUBAP-01-2021-47).