New Insights into Paenibacillus larvae Bacteria – an Agent Causing American Foulbrood Infections Using Next-Gen Biotics with Antimicrobial Properties In Vivo

Paenibacillus larvae is the causative agent of American foulbrood, a severe bacterial brood disease of honeybees. Worldwide, three main strategies are used to control and prevent this infection: antibiotic therapy, rigorous disinfection and maintenance of en-vironmental sterility, and biotechnical interventions. This study aimed to evaluate under field conditions a fourth preventive strategy based on a next-generation biotic administered to honeybee colonies without risk of food or environmental contamina-tion. The product was developed through microbial biotechnology. The experiment involved assessing the microbial load and quantifying P. larvae in the native microbi-ome of 40 honeybee colonies, divided into three treatment groups and one control. Colonies received the pharmacobiotic in defined doses through three application methods. At the end of the trial, reductions in P. larvae abundance were assessed. Using parametric ANOVA tests, boxplots, and spaghetti plots, it was shown that within four weeks, P. larvae were eliminated from the microbiome of the treated colonies. All three delivery methods produced this effect. Additionally, the microbiota of the treated col-onies was enriched with lactic acid bacteria, whose abundance increased by up to six logarithmic orders. This preventive approach aligns with Evidence-Based Practices and supports biosafety and metaphylaxis strategies recommended for sustainable bee-keeping management.