In Vitro Characterization and Safety Assessment of Streptococcus salivarius, Levilactobacillus brevis and Pediococcus pentosaceus Isolated from the Small Intestine of Broiler Breeders

In poultry production, antibiotics have been excessively used as growth promoters to support well-being and decrease mortality caused by pathogenic microorganisms. The overuse of antibiotics has led to the emergence of antibiotic-resistant bacteria and the presence of antibiotic residues in poultry products. To counteract this problem, probiotics could be used as adjuncts or as substitutes for preserving a diverse and balanced microflora to prevent the colonization and multiplication of pathogenic bacteria in the GI tract. This study aimed to isolate and characterize the potential probiotic properties of lactic acid bacteria from the small intestine of 23-week-old broiler breeders, with the goal of identifying potential probiotic candidates. Four phenotypically healthy broiler breeders were selected, and intestinal contents were aseptically collected and cultured on MRS agar. From the initial pool of 39 colonies, six isolates were identified based on Gram-positive and catalase-negative characteristics and further classified using 16S rRNA sequencing as Levilactobacillus brevis (n = 3), Pediococcus pentosaceus (n = 2), and Streptococcus salivarius (n = 1). These strains were further evaluated for probiotic properties such as transit resistance to simulated upper gastrointestinal conditions, antagonist activity, haemolytic activity, and cell surface properties such as autoaggregation, co-aggregation and hydrophobicity, in vitro. L. brevis NKFS8 showed good tolerance to pH 3, while P. pentosaceus NKSF10 exhibited good tolerance to pH 4 acidic conditions. All isolates demonstrated good survivability in bile salt concentration of 3% (w/v), with P. pentosaceus NKSF10 exhibiting the highest tolerance. The isolates showed a wide range of antagonistic activity against the test pathogens Pseudomonas aeruginosa (ATCC 27853), Salmonella typhimurium, Salmonella enterica (ATCC 13314), Staphylococcus aureus (ATCC 29213), and Listeria monocytogenes (ATCC 7644). Furthermore, these strains exhibited good auto-aggregation, co-aggregation, and hydrophobicity properties. In conclusion, lactic acid bacteria from the small intestine of broiler breeders present a valuable prospect for the development of effective probiotics. These probiotics can be utilized as a supplementary inclusion in poultry feed, obviating the need for antibiotics as growth promoters. Nevertheless, additional in vivo studies are required to closely monitor and assess the effects of probiotics on the gastrointestinal system of chickens.