Honeybees exposure to veterinary drugs: how the gut microbiota is affected

Abstract

Several studies have outlined that a balanced gut microbiota offers metabolic and protective functions supporting honeybee health and performances. The present work contributes to increasing knowledge on the impact on the honeybee gut microbiota of the administration of three different veterinary drugs (oxytetracicline, sulphonamides and tylosin). The trial was designed with a semi-field approach in micro-hives containing about 500 bees, i.e. in experimental conditions as close as possible to real hives considering the restrictions on the use of antibiotics; 6 replicates were considered for each treatment plus the control. The absolute abundance of the major gut microbial taxa in newly eclosed individuals was studied with qPCR and next generation sequencing. Antimicrobial resistance genes for the target antibiotics were also monitored using a qPCR approach. The results showed that none of the veterinary drugs altered the total amount of gut bacteria, but qualitative variations were observed. Tylosin treatment determined a significant decrease of α- and β-diversity indexes and a strong the depletion of the rectum population (lactobacilli and bifidobacteria) while favoring the hindgut population (Gilliamella, Snodgrassella and Frischella spp.). Major changes were also observed in honeybees treated with sulphonamides, with a decrease in Bartonella and Frischella core taxa an increase of Bombilactobacillus spp. and Snodgrassella spp. Conversely, minor effects were observed in oxytetracycline treated honeybees. Monitoring of antibiotic resistance genes confirmed that honeybees represent a great reservoir of tetracycline resistance genes. Tetracycline and sulphonamides resistant genes tended to increase in the gut microbiota population upon antibiotic administration. Importance This study investigates the impact of the three most widely used antibiotics in the beekeeping sector (oxytetracycline, tylosin and sulphonamides) on the honeybee gut microbiota and on the spread of antibiotic resistance genes. The research represents an advancement to the present literature considering that tylosin and sulphonamides effect on the gut microbiota has never been studied. Another original aspect lies in the experimental approach used, as the study looks at the impact of veterinary drugs and feed supplements 24 days after the beginning of the administration, thus exploring perturbations in newly eclosed honeybees, instead of the same treated honeybee generation. Moreover, the study is not performed with cage tests but in micro-hives thus reaching conditions closer to real hives. The study reaches the conclusion that tylosin and sulfonamides determine major changes in some core members and that antibiotic resistance genes for tetracycline and sulphonamides increase upon antibiotic treatment.