Isolation, identification and determination of antimicrobial activities of probiotic microorganisms from various sources

Probiotics are live microorganisms that exert beneficial effects on health and help regulate the digestive system. Lactic acid bacteria, among the most prominent probiotic microorganisms, play a crucial role in improving gut health. Due to their ability to withstand stressful conditions such as varying concentrations of acid, bile, and phenol, and their capacity to produce various metabolites, these bacteria are considered potential probiotics. This study aimed to isolate, identify, and characterize certain probiotic properties of microorganisms found in various food sources, including dates, dried figs, apricots, yogurt, vinegar, and pickles. MRS (De Man, Rogosa, and Sharpe) agar and broth media were used for isolation. The samples were incubated at 37 °C for 24–48 hours, and colonies with different morphologies were selected to obtain pure cultures. A total of 10 isolates were purified, their probiotic characteristics were examined, and those with probiotic potential were identified by molecular methods. Among the 10 isolates, one was found to be Gram-negative, while the remaining nine were Gram-positive. According to the catalase test results, eight isolates were catalase-positive and two were catalase-negative. Isolates 3 and 6, both Gram-positive and catalase-negative, were identified by molecular methods. To assess their probiotic potential, acid tolerance, bile and phenol tolerance, hemolytic activity, antibiotic susceptibility, and antimicrobial activity tests were conducted. The acid tolerance test revealed that both isolates could grow at pH 3. In the bile salt tolerance test, both showed strong resistance to high concentrations. Isolate 3 exhibited a stable growth profile against increasing phenol concentrations, indicating high tolerance. Antibiotic susceptibility tests showed that isolate 3 was moderately sensitive to gentamicin while isolate 6 was resistant; both isolates were resistant to vancomycin. Neither isolate demonstrated hemolytic activity, indicating no ability to lyse erythrocytes. No antimicrobial activity was observed for either isolate. Based on molecular identification, isolates 3 and 6 were identified as Leuconostoc mesenteroides and Lactobacillus paracasei, respectively.