Phenotypic Screening and Antimicrobial Activity of Probiotic Candidates from Piglets

Lactic acid bacteria are commonly investigated as probiotic microorganisms for improving gut health and reducing antibiotic use in swine production. This study aimed to isolate and perform preliminary phenotypic screening of presumptive probiotic bacteria from feces of healthy piglets raised without antibiotic or probiotic supplementation. Fecal samples (n = 42) were collected from piglets of different ages, and LAB isolates were obtained using selective culture-based methods. A total of 135 Gram-positive, cata-lase-negative bacilli were subjected to in vitro evaluation of selected probiotic-related characteristics, including tolerance to acidic and bile conditions, cell surface hydropho-bicity, hemolytic activity, and antimicrobial activity against swine-associated indicator bacteria. Two isolates (PMvet212 and PMvet318) survived exposure to pH 3.1 with less than 1 log CFU/mL reduction and tolerated 0.3% bile salt, while PMvet212 also survived at 0.5% bile salt. Both isolates exhibited low hydrophobicity values (7.85–12.38%) and showed alpha-hemolytic activity. Cell-free supernatants from these isolates inhibited Escherichia coli isolated from diarrheic piglets and Staphylococcus aureus ATCC 6538, with inhibition zones classified as intermediate. Overall, the results indicate that a limited number of piglet-derived isolates exhibit in vitro tolerance to gastrointestinal stress con-ditions and moderate antimicrobial activity. This study provides preliminary data to support further identification, safety assessment, and in vivo evaluation of selected isolates for potential application in swine health management.