Synergistic antimicrobial and probiotic activity of lactic acid bacteria isolated from Tarkhineh against Candida albicans.

The aim of the study was to isolate and characterize lactic acid bacteria (LAB) from traditional dairy products (tarkhineh) in Kermanshah in western Iran, with a view to their probiotic potential and antimicrobial activity (Candida albicans). A total of 60 tarkhineh samples were randomly screened to isolate the probiotic bacterial strains. Biochemical and physiological analysis confirmed that the isolates were Gram-positive, catalase-negative, and had a round or rod-shaped morphology, in accordance with the LAB classification. Out of 20 isolated strains, five (Ta12, Ta19, Ta37, Ta51, and Ta58) showed a high survival rate (> 94%) under the initial acidity and bile salt screening conditions, which led to their selection for further study. The rescreening confirmed that these strains can survive (> 54%) in enzymatic conditions of the gastrointestinal tract, including the stomach and intestinal tracts. All five strains showed significant antimicrobial activity against 12 common human pathogens, predominantly Gram-positive species, exhibiting inhibition zones ranging from 13.33 to 25.33 mm. Immunological tests revealed negative hemolysis (γ-hemolysis), which indicates that all five strains are safe. However, strains of Ta19 and Ta51 demonstrated higher susceptibility to nine common antibiotics (cefixime, azithromycin, amoxicillin, doxycycline, sulfamethoxazole, ciprofloxacin, cephalexin, amoxicillin-clavulanic acid, and vancomycin), as evidenced by susceptibility spectrum ranging from 12.00 to 39.67 mm. In addition, these two strains showed superior hydrophobicity (> 57%), satisfactory cell adhesion (> 41%), increased cholesterol uptake (> 37%), enhanced biofilm formation (> 26%), and improved properties of auto-aggregation (> 43%) and co-aggregation (> 36%). Antifungal tests showed that Ta19 at 10 CFU/mL and Ta51 at 10 CFU/mL effectively inhibited the activity of C. albicans in comparison with other strains. The bacteriocin (protein) nature of the effective extracts from these two strains against the above-mentioned pathogenic microorganisms has also been confirmed. In addition, the combination of 25 percent extract from strain Ta19 and 75 percent extract from strain Ta51 demonstrated superior antifungal properties compared with the other formulations and the control strain of the bacterium (Lactiplantibacillus plantarum subsp. plantarum PTCC 1745) and antibiotic (fluconazole). 16S rRNA sequencing with 99.99% similarity identified strains Ta12, Ta19, Ta37, Ta51, and Ta58 as Lactobacillus delbrueckii, Lactiplantibacillus plantarum subsp. plantarum, Lactococcus lactis, Leuconostoc mesenteroides, and Lactobacillus johnsonii, respectively. In conclusion, a new bacterial extract formulation containing 25% L. plantarum subsp. plantarum Ta19 and 75% L. mesenteroides Ta51 has potential as a powerful probiotic against Candida.