In Vitro Characterization of Probiotic-Associated and Safety-Related Properties of Five Lactic Acid Bacterial Cultures

Abstract

Probiotic microorganisms, particularly lactic acid bacteria (LAB), have been investigated for their ability to tolerate gastrointestinal conditions and inhibit pathogenic bacteria. In this study, five strains, Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus rhamnosus, Lactobacillus plantarum and Lactococcus lactis, were characterized for a range of probiotic-associated properties. Acid and bile tolerance, sodium chloride tolerance, antimicrobial activity against Escherichia coli and Staphylococcus aureus, antioxidant activity and antibiotic susceptibility were examined. All five strains remained viable at pH 2.0 and tolerated bile salts at concentrations of up to 1.0%. During exposure to simulated gastric conditions, L. rhamnosus showed the highest survival, followed by L. plantarum and L. acidophilus. Antimicrobial testing resulted in inhibition zones of 8-11 mm against the two indicator pathogens, with L. rhamnosus producing the largest zones. All strains also showed DPPH radical-scavenging activity, ranging from 54.6% to 72.3%, and the highest value was recorded for L. plantarum. Preliminary phenotypic screening showed that all cultures were non-hemolytic, catalase-negative and non-motile under the conditions tested. The combined results demonstrate differences among the strains in gastrointestinal stress tolerance and functional activities, with L. rhamnosus and L. plantarum showing comparatively stronger performance in several of the evaluated assays. These findings provide a basis for further strain-specific assessment of their suitability for functional food and dietary applications.