Investigation of synergistic effects of Microcystis aeruginosa (Kützing) kützing 1846 metabolites with different antibiotic combinations

Aim of the study, laboratory investigations and experiments were conducted to detect the synergistic effects of different antibiotics with the metabolites of Microcystis aeruginosa, a cyanobacterial species. In line with this objective, it was determined that M. aeruginosa entered the exponential growth phase on the 42nd day, and experiments were planned according to the culture development. Extracts were prepared from cultures aged 45, 60, and 90 days. Antimicrobial activity studies and synergy tests were conducted to determine the Minimum Inhibitory Concentration (MIC) values of the obtained extracts. Antimicrobial activity tests were performed according to the recommendations of the Clinical and Laboratory Standards Institute (CLSI) M100-S28 and M27-A3. Standard strains used included Staphylococcus aureus ATCC 29213, Enterococcus faecalis ATCC 29212, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, and Candida albicans ATCC 10231. According to the experimental results, no significant difference was observed among the 45-day culture extracts against Gram-negative bacteria, while variations in activity levels were observed against Gram-positive bacteria. Synergy tests conducted using the checkerboard method revealed an additive effect on P. aeruginosa with the combination of the 60-day culture extract and gentamicin, with a threefold decrease in the MIC value.