Antimicrobial Activity of Cell-Free Supernatants Produced by Strains of Lactic Acid Bacteria Against Staphylococcus aureus

Bacterial zoonoses pose a serious threat to the development of animal husbandry, food safety, and public health. Staphylococcus aureus (S. aureus) is a major infectious and food-borne pathogen worldwide, and there was an urgent need to develop relevant methodologies for the control of bacterial infections. This study aimed to evaluate the effectiveness of cell-free supernatants (CFSs) produced by selected strains of Lactiplantibacillus plantarum (L. plantarum), Lacticaseibacillus rhamnosus (L. rhamnosus), Streptococcus thermophilus (S. thermophilus), and Bifidobacterium longum subspecies infantis (B. infantis) to inhibit in vitrogrown S. aureus BNCC 186335. CFSs of S. thermophilus, B. infantis, L. plantarum, and L. rhamnosus not only showed good antibacterial activity against S. aureus but also have strong stability and tolerance, which could destroy the integrity of cell membrane, lead to changes in cell morphology, and then strongly and rapidly kill bacteria. Notably, the primary antimicrobial substances in the CFSs of L. plantarum and L. rhamnosus were organic acids and protein components, whereas the main antimicrobial substances in the CFSs of S. thermophilus and B. infantis were organic acids. Meanwhile, four CFSs achieved substantial removal of biofilms and inhibited decreased ATP content. These findings suggest that the CFSs of S. thermophilus, B. infantis, L. plantarum, and L. rhamnosus may have potential applications as biological preservatives to control the contamination of S. aureus in the food industry and animal husbandry.