Probiotic Assessment of Lactic Acid Bacteria Strains and Consortia for Enhancing Honey Bee Health and Nutrition

The decline of honey bee health has intensified interest in microbiome-based strategies to support colony resilience and reduce reliance on chemical interventions. In this study, we performed an in vitro probiotic screening of five lactic acid bacteria (LAB) strains of honey bee origin and two multi-strain consortia for prospective application in apiculture. Two formulations were evaluated: LAB Mix 1 (<i>Apilactobacillus kunkeei</i> and <i>Lactobacillus apis</i>) and LAB Mix 2 (<i>Lactiplantibacillus plantarum</i>, <i>Fructobacillus fructosus</i>, and <i>A. kunkeei</i>). Functional and safety-related traits were investigated, including auto-aggregation, cell-surface hydrophobicity, inter-strain compatibility, organic acid production, oxidative detoxification capacity, antibiotic susceptibility, haemolytic activity, and growth dynamics in sugar-based feeding syrups. All strains exhibited time-dependent increases in aggregation and hydrophobicity, with <i>A. kunkeei</i> and <i>F. fructosus</i> showing particularly strong surface-associated properties. No mutual antagonism or haemolytic activity was observed. Organic acid profiling revealed strain-specific metabolic signatures, with high lactic and citric acid production by <i>L. plantarum</i> and LAB consortia. Several strains displayed peroxidase activity, suggesting a role in oxidative stress mitigation. Growth assays demonstrated that high sugar concentrations severely limited bacterial growth, whereas moderate dilution significantly improved growth. Under osmotic stress conditions, mixed cultures generally achieved higher optical density values than individual strains. Collectively, these findings support bee-associated LAB and multi-strain formulations as promising candidates for further probiotic development.