LAUSR

The objectives of this investigation were a) to isolate bacteria from different foods (dairy products, fruits, and vegetables) and evaluate their probiotic potential and b) to select, identify, and characterize the strain with the highest probiotic potential. From 14 food samples, a total of 117 strains were isolated; however, only 42 (T1 to T42) showed the morphology (gram-positive, coco, and bacillar form) and were catalase- and oxidase-negative to be considered as a presumptive lactic acid bacteria (LAB). The antagonistic activity of the 42 strains was evaluated on Escherichia coli (O157:H7E09), Listeria monocytogenes (ATCC 19115), Staphylococcus aureus (ATCC 25923), and Salmonella enterica serotype Typhimurium (ATCC 14028). The strains with the highest antagonistic activity were nine isolates from the following: pulque (T1), sprouted beans (T26), ranchero cheese (T30, T31, T32, T33, T35, T36), and tenate cheese (T40) with inhibition zones from 17.0 ± 1.2 to 19.3 ± 2.8 mm. Based on the antagonistic activity against pathogenic bacteria and resistance to low pH and bile salts, strain T40 exhibited the highest probiotic potential. Using the 16S rRNA technique, strain T40 was identified as Lacticaseibacillus paracasei (the previous taxonomic nomenclature was Lactobacillus paracasei , prior to the nomenclature change in April 2020); this strain presented no resistance to ampicillin, gentamicin, erythromycin, and tetracycline. The antagonistic activity was evaluated in situ (fresh cheese) against pathogenic bacteria, evidencing the probiotic potential of L. paracasei . Finally, Lacticaseibacillus paracasei isolated from tenate cheese showed characteristics as a probiotic microorganism and high potential in food technology.