In Vitro Phenotypic Screening and MALDI-TOF Identification of Lactic Acid Bacteria Isolated from Feces of Suckling Piglets with Antibacterial Activity

Lactic acid bacteria are important components of the early gut microbiota in piglets and may contribute to gastrointestinal stability and control of enteric pathogens, particularly under increasing restrictions on antibiotic use in livestock production. This study aimed to perform in vitro phenotypic screening and characterization of lactic acid bacteria isolated from feces of suckling piglets aged 7–28 days. A total of 42 fecal samples were collected and cultured on selective media, yielding 318 colonies, of which 135 Gram-positive, rod-shaped, catalase-negative isolates were selected for further evaluation. These isolates were assessed for tolerance to acidic conditions (pH 2.0–3.1), bile salts (0.3–0.5%), cell surface hydrophobicity, hemolytic activity, and antibacterial activity against Escherichia coli and Staphylococcus aureus. Among the tested isolates, only two (PMvet212 and PMvet318) demonstrated limited tolerance to acidic and bile conditions and exhibited moderate antibacterial activity, with inhibition zones of approximately 10–12 mm. Identification using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry indicated that PMvet212 was closely related to Lactobacillus brevis, whereas PMvet318 was identified at the genus level as Lactobacillus sp. However, both isolates exhibited α-hemolytic activity and therefore did not meet the safety criteria required for probiotic application. In conclusion, although piglet-derived lactic acid bacteria may exhibit certain functional properties, the present findings highlight that probiotic potential is strain-specific and that rigorous multi-step screening, together with further in vivo validation, is essential before practical application can be considered.