Lactobacillus kunkeei impacts the health of honey bees, Apis mellifera scutellata, and protects the bees against the opportunistic pathogen Serratia marcescens

Abstract

The honey bee, Apis mellifera, is the most critical managed agricultural pollinator and its recent colony losses is of global concern. Bacterial pathogens are one of the causes attributed to the decline of the bee population. Serratia marcescens is an opportunistic pathogen with a broad host range, capable of affecting various plants and animals. S. marcescens can invade various tissues of the honey bee, including the gut and hemolymph, leading to severe infections and compromising bee health. S. marcescens is often associated with secondary infections, and can rapidly multiply forming biofilms, making it particularly challenging to control and eliminate. Understanding the interactions between S. marcescens and the honey bee, as well as exploring potential solutions such as probiotics, is crucial for bee health improvement. In this study, we assessed the effect of Lactobacillus kunkeei, a bee gut associated bacterium on honey bee survival, protection against the opportunistic pathogen S. marcescens, and activation of bee immune responses. Newly emerged worker bees were divided into groups: MD- no treatment, GH-inoculated with hive bees’ gut homogenate and Lk- inoculated with L. kunkeei. After five days of inoculation, bees in each respective group were exposed to the opportunistic pathogen S. marcescens. Our results show that L. kunkeei increased bee survival after S. marcescens infection, inhibited its proliferation in the gut, and reduced antimicrobial peptide genes expression in the gut epithelium compared to microbe-deprived bees in a laboratory