Title:A mézelő méhek (Apis mellifera) nyúlós költésrothadását okozó hazai Paenibacillus larvae törzsek NAF gyógyhatású állatgyógyászati készítménnyel szembeni in vitro érzékenységének jellemzése
SUMMARY Background: American foulbrood (AFB) is the most important bacterial dis ease of honeybees with worldwide distribution, which causes high economic losses. The causative agent is P. larvae a Gram-positive, rod-shaped, motile, spore forming bacterium species. Usage of antibiotics for treatment of this dis ease is not allowed in most countries because of the residues in honey and other bee-products. Therefore, there is a great interest to find alternative and effective AFB-controlling natural substances, such as plant essential oils, which have natural antibacterial effect. Objectives: Antibacterial activity (Minimal Inhibitory Concentration) of a veteri nary medical product called „NAF” (Chemor Ltd., Hungary) against 30 P. larvae strains isolated from different area of Hungary was determined. Strains originat ing from Hungarian apiaries were isolated and identified in 2015. Materials and Methods: Vegetative cells of P. larvae were grown on Columbia Agar supplemented with 10% defibrinated sheep blood. Bacterial suspension was set to MacFarland standard 0.5 that corresponds with 105 CFU/ml bacterial density. Determination of MIC-values were carried out using broth dilution method in 48-well tissue culture plates. After the inoculation of the bacteria the tissue cul ture plates were incubated at 37 ºC for 48 hours. After the incubation period the bacterial growth was evaluated with naked eye. Results and Discussion: MIC range of NAF veterinary medical product was between 0.015 and 1.953 µl/ml in case of the investigated P. larvae strains. MIC50 and MIC90 values were both determined as 0.997 µl/ml. In vivo effect of the product should be carefully evaluated due to the poor infor mation about the concentration of the active ingredients in the royal jelly. There fore, conclusion about in vivo efficacy of the product should not be deducted, based on the in vitro susceptibility of the vegetative from of the pathogen.