In Vitro Antagonistic Effect of Gut Bacteriota Isolated from Indigenous Honey Bees and Essential Oils against Paenibacillus Larvae

The aim of study was to isolate and identify the gut bacteria ofApis melliferaand to evaluate antagonistic effect of the bacteriota againstPaenibacillus larvae, which causes American foulbrood (AFB) in honeybees. The dilution plating method was used for the quantification of selected microbial groups from digestive tract of bees, with an emphasis on the bacteriota of the bees' intestines. Bacteria were identified using mass spectrometry (MALDI-TOF-MS Biotyper). Overall, five classes, 27 genera and 66 species of bacteria were identified. GeneraLactobacillus(10 species) andBacillus(8 species) were the most abundant. Gram-negative bacteria were represented with 16 genera, whereas Gram-positive with 10 genera.Delftia acidovoransandEscherichia coliwere the most abundant in the digestive tract of honey bee. Resistance to a selection of antimicrobials was assessed for the bacterial isolates from bee gut and confirmed against all antimicrobials included in the study, with the exception of cefepime.Lactobacillusspp., especiallyL. kunkeei,L. crispatusandL. acidophilus. showed the strongest antimicrobial activity againstP. larvae, the causal pathogen of AFB. Antimicrobial activity of essential oils against isolated bacteria and two isolates ofP. larvaewere assessed. Application of a broad selection of plant essential oils indicated thatThymus vulgarishad the highest antimicrobial activity againstP. larvae.