Sporicidal evaluation of different substances against Nosema ceranae for surface disinfection

Nosema ceranae is the microsporidium causing a disease highly prevalent in honey bees. Since few treatments are available to control this disease, cleaning and disinfection of beekeeping equipment could be a useful tool for decreasing the number of viable spores and therefore the risk of infection. Up to date, the information about the efficacy of substances suitable for beekeeping use is scarce. In this work, the sporicidal activity of different products against N. ceranae spores has been tested using a new method here developed based on International harmonisation norms. Stainless steel surfaces (5 cm2) were contaminated with 100,000 fresh percoll® purified N. ceranae spores. The surfaces were exposed for 5 and 15 minutes with different products selected either because they are common use disinfectants (sodium hypochlorite, acetic acid, ethanol 96°, ammonia solution, or povidone-iodine), or because they are commercial products marketed for surface disinfection (Inokuo®, Mycoplasma OFFTM, Biocidal ZFTM) or for Varroa control (Ecoxal). After exposure, the viability of spores was analysed by flow cytometry after staining with propidium iodide solution and compared to spores exposed to water (negative control) or autoclaved (positive control). Among tested products, ammonia solution, sodium hypochlorite and Mycoplasma OFFTM, showed sufficient effect to be used in equipment disinfection. Other products as acetic acid causing an increase of cell debris could be also useful although they require further investigations. Graphical Abstract