2.3.1. Spore Viability and Germination Test

Fungal cultures of A. apis DSM 3116 and A. apis 3117 were cultured in MEA medium at 28 °C for 15 days in aerobiosis. A spore suspension was obtained by washing the ascospores that formed on the surfaces of plates with 5–10 mL of 0.01% sterile Tween-80. The suspension was collected in a sterile 100 mL Erlenmeyer flask and loosened by shaking with sterile glass beads for 2 h. The germination test was conducted according to the procedure described by Jensen et al. [57] with some modifications. Briefly, sterile Teflon-coated slides (TEKDON, Myakka City, FL, USA) were placed in a sterile Petri dish lined with wet filter paper. Then, 100 μL of spore suspension (about 10⁷ spores/mL) was mixed with 400 μL of GLEN medium [57] and 100 μL of LAB culture (grown in MRS broth at 37 °C for 24 h), and 10 μL of this spore/GLEN/LAB (SGL) mixture was placed onto the Teflon-coated slides. A spore/GLEN (SG) mixture without LAB cultures was used as a control. To stimulate germination, the Petri dish was exposed for 10 min to 9–13% CO₂ [58] using an AnaeroGen sachet in a 3.5 L jar (Oxoid; Basingstoke, UK), and after 32 h at 34 °C in aerobiosis, we counted the spores directly on the Teflon slide. About 100 spores were counted in three different fields of view on the slide using a phase contrast microscope at 400× magnification (Axioplan, Zeiss; Göttingen, Germany). Spores were considered germinated when the length of a hypha was longer than the length of the diameter of the spore. All the chemical compounds were supplied by Sigma–Aldrich (St. Louis, MO, USA). The tests were conducted in triplicate.