EVALUATION OF THE ANTIMICROBIAL ACTIVITY OF KOMBUCHA UNDER DIFFERENT FERMENTATION CONDITIONS

INTRODUCTION: Kombucha is a fermented beverage produced through the symbiotic activity of bacteria and yeasts, whose composition may contain compounds with potential antimicrobial activity. AIMS: The present study aimed to determine the antimicrobial activity of kombucha prepared under different fermentation conditions through in vitro susceptibility tests against potentially pathogenic bacterial strains. MATERIALS AND METHODS: Kombuchas produced with green tea and yerba mate tea were evaluated using sucrose concentrations of 5%, 10%, and 15%, with samples collected on fermentation days 0, 1, 3, 5, 8, 12, and 15, in addition to an additional sample collected on day 24. Antimicrobial activity was initially evaluated using the agar well diffusion method against five bacterial species: Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Salmonella Typhimurium, and Pseudomonas aeruginosa, with ampicillin, gentamicin, ciprofloxacin, and meropenem used as positive controls. Subsequently, the minimum inhibitory concentration (MIC) was determined using the broth microdilution method in Mueller-Hinton broth, using 15% sucrose green tea and yerba mate kombuchas and the antibiotics ampicillin and tetracycline. RESULTS: In the agar diffusion assay, the kombucha samples did not produce measurable inhibition zones under the experimental conditions employed. This result was interpreted considering methodological limitations related to well dimensions, sample application, and storage conditions, including freezing periods and repeated freeze-thaw cycles. In contrast, the MIC assay demonstrated inhibitory activity of the kombucha samples against the evaluated bacteria, with greater activity generally observed during the later stages of fermentation. On day 24, the green tea kombucha presented MIC values of 50 µL against Escherichia coli, Salmonella Typhimurium, Pseudomonas aeruginosa, Enterococcus faecalis, and Staphylococcus aureus. For yerba mate kombucha, MIC values of 50 µL were observed against Salmonella Typhimurium, Pseudomonas aeruginosa, and Enterococcus faecalis, whereas Escherichia coli and Staphylococcus aureus presented MIC values of 75 µL and 100 µL, respectively. Variations in MIC values were observed throughout fermentation, potentially associated with the dynamics of the fermentation process and sample storage conditions. Based on the limitations identified, a new experimental batch was initiated using exclusively 15% sucrose and different fermentation volumes, aiming to improve experimental standardization and reduce sources of variability. FINAL CONSIDERATIONS: The results demonstrate the antimicrobial potential of the evaluated kombuchas and provide a basis for further investigation into the influence of fermentation conditions on the antimicrobial activity of the beverage.

PALAVRAS-CHAVE: Kombucha; Fermentation; Antimicrobial activity; Minimum inhibitory concentration; Bacteria.