The contamination of food products by psychrotrophic microorganisms, particularly Pseudomonas aeruginosa (P. aeruginosa), presents a significant challenge to food quality and safety in the dairy industry. Although not a foodborne pathogen, P. aeruginosa is highly destructive to food stability, leading to spoilage and reduced shelf life. This study investigates the interactions between P. aeruginosa, several foodborne pathogens, yogurt starter cultures, and spoilage fungi using dual-culture assays. P. aeruginosa exhibited strong antagonistic effects on various microorganisms and demonstrated inhibition of pathogens through metabolic compounds such as hydroxyurea, pentane-1, 5-diol, ethylmethylsilane, and N-benzylidene-dimethylammonium chloride, identified via GC-MS analysis. To counteract P. aeruginosa, the protective lactic acid bacterium Limosilactobacillus reuteri (L. reuteri) was employed. The bacterium enhanced the sensitivity of P. aeruginosa to several antibiotic classes, including aminoglycosides, beta-lactams, cephalosporins, and chloramphenicol. GC-MS profiling of L. reuteri extracts revealed potent bioactive compounds, such as derivatives of D-lactic acid, phenyllactic acid, and hydroxyisocaproic acid, which possess robust antimicrobial properties. When applied in fermented milk, L. reuteri extracts (2 mg/mL) completely inhibited the growth of P. aeruginosa while preserving the functionality of yogurt starter cultures during storage. These findings highlight the potential of L. reuteri as a bio-protective agent to mitigate spoilage in dairy products.