title: Quantifying spore viability of the honey bee pathogen Nosema apis using flow cytometry.
abstract: Honey bees are hosts to more than 80 different parasites, some of them being highly virulent and responsible for substantial losses in managed honey bee populations. The study of honey bee pathogens and their interactions with the bees' immune system has therefore become a research area of major interest. Here we developed a fast, accurate and reliable method to quantify the viability of spores of the honey bee gut parasite Nosema apis. To verify this method, a dilution series with 0, 25, 50, 75, and 100% live N. apis was made and SYTO 16 and Propidium Iodide (n = 35) were used to distinguish dead from live spores. The viability of spores in each sample was determined by flow cytometry and compared with the current method based on fluorescence microscopy. Results show that N. apis viability counts using flow cytometry produced very similar results when compared with fluorescence microscopy. However, we found that fluorescence microscopy underestimates N. apis viability in samples with higher percentages of viable spores, the latter typically being what is found in biological samples. A series of experiments were conducted to confirm that flow cytometry allows the use of additional fluorescent dyes such as SYBR 14 and SYTOX Red (used in combination with SYTO 16 or Propidium Iodide) to distinguish dead from live spores. We also show that spore viability quantification with flow cytometry can be undertaken using substantially lower dye concentrations than fluorescence microscopy. In conclusion, our data show flow cytometry to be a fast, reliable method to quantify N. apis spore viabilities, which has a number of advantages compared with existing methods.
authors: Centre for Integrative Bee Research (CIBER), The University of Western Australia, Crawley, Western Australia, 6009, Australia; ARC Centre of Excellence in Plant Energy and Centre for Comparative Analysis of Biomolecular Networks (CABIN), The University of Western Australia, Crawley, Western Australia, 6009, Australia.
authors: Yan
authors: Y
authors: Peng
authors: Tracey F
authors: TF
authors: Lee-Pullen
authors: Kathy
authors: K
authors: Heel
authors: A Harvey
authors: AH
authors: Millar
authors: Boris
authors: B
authors: Baer
mesh_terms: D000818:Animals; D001516:Bees / Q000382:microbiology*; D002470:Cell Survival / Q000502:physiology; D005434:Flow Cytometry; D005456:Fluorescent Dyes; D016818:Nosema / Q000302:isolation & purification / Q000472:pathogenicity*; D013172:Spores, Fungal / Q000302:isolation & purification* / Q000472:pathogenicity
chemical_list: D005456:Fluorescent Dyes
keywords: Nosema apis; Propidium Iodide; SYBR 14; SYTO 16; SYTOX Red; flow cytometry; fluorescence microscopy; microsporidia; viability