Investigation of synergistic interactions between antiseptics and antibiotics against Enterococcus faecalis and Enterococcus faecium strains isolated from clinical specimens

One of the major issues of our time is antimicrobial resistance, and enterococci are among the pathogens categorized as "high priority" by the World Health Organization. One alternative approach to antibiotic resistance is combination strategies. Enterococcal strains are frequently isolated from clinical specimens, and Enterococcus faecalis stands out as a leading pathogen in secondary apical periodontitis, which develops as a result of unsuccessful dental endodontic treatments. There is currently no ideal antiseptic for use in wound and endodontic infections. Research into alternative antiseptics for these infections continues to this day. In this study, a total of 50 enterococcal strains were selected, including 30 Enterococcus faecalis and 20 Enterococcus faecium strains isolated from 40 wound specimens, 6 abscesses, and 4 rectal swabs. Throughout the study, Enterococcus faecalis ATCC 29212 and Enterococcus faecium ATCC 6057 were used as control strains. The minimum inhibitory concentrations of antibiotics and antiseptics were determined using the broth microdilution method according to the European Committee on Antimicrobial Susceptibility Testing criteria, while combination tests were conducted using the checkerboard method. Antibiotic-antiseptic combinations have been found to mostly exhibit synergistic or partially synergistic effects against enterococcal strains. This study demonstrated that the minimum inhibitory concentrations of antibiotics could be reduced through potential interactions with antiseptics, supporting the idea that combining antiseptics with antibiotics could lower bacterial resistance levels and reduce the frequency of antibiotic resistance emergence. Keywords: Antibiotics, antiseptics, checkerboard, combination, enterococcus