Viability and infectivity of fresh and cryopreserved Nosema ceranae spores.
The microsporidium fungus Nosema ceranae is an intracellular parasite that infects the midgut of the honey bee, Apis mellifera. A major limitation of research on N. ceranae is that the fungus is non-culturable and thus studying it depends on the seasonal availability of Nosema spores. Also, spore viability and infectivity can vary considerably, and thus there is a need for reliable methods for determining those traits. This study examined different conditions for N. ceranae spore cryopreservation at -70°C, assessing spore viability and infectivity. Viability was determined by a staining procedure counting total spores numbers with bright field microscopy and un-viable spore numbers with the fluorescent dye, propidium iodide. Spore infectivity was determined with a dilution inoculation assay. Infectivity was dependent on the inoculum dose for the proportion of bees with detectable Nosema infections based on the number of spores per bee at 18days after inoculation; 4000 spores per bee or higher were needed to get approx. 100% of the inoculated bees infected. The median infective dose (ID50) was 149 spores per bee, and the minimum dose capable of causing a detectable infection was 1.28 spores. The proportion of N. ceranae infected bees correlated significantly with the number of spores per bee (r=0.98, P<0.0001). N. ceranae spores cryopreserved in water or 10% glycerol did not differ in viability compared to fresh spores, but lost infectivity when inoculated into bees. This study shows that while cryopreservation of N. ceranae spores can preserve viability, the spores can have reduced infectivity.
School of Environmental Sciences, University of Guelph, 50 Stone Road East, Guelph, Ontario N1G2W1, Canada.
Janine
J
McGowan
Departamento de Producción Animal: Abejas, FMVZ, UNAM, Cd. Univ., Mexico DF 04510, Mexico.
Alvaro
A
De la Mora
School of Environmental Sciences, University of Guelph, 50 Stone Road East, Guelph, Ontario N1G2W1, Canada.
Paul H
PH
Goodwin
School of Environmental Sciences, University of Guelph, 50 Stone Road East, Guelph, Ontario N1G2W1, Canada.
Marc
M
Habash
School of Environmental Sciences, University of Guelph, 50 Stone Road East, Guelph, Ontario N1G2W1, Canada.
Mollah Md
MM
Hamiduzzaman
School of Environmental Sciences, University of Guelph, 50 Stone Road East, Guelph, Ontario N1G2W1, Canada.
Paul G
PG
Kelly
School of Environmental Sciences, University of Guelph, 50 Stone Road East, Guelph, Ontario N1G2W1, Canada. Electronic address: eguzman@uoguelph.ca.
Ernesto
E
Guzman-Novoa
D000818:Animals; D001516:Bees / Q000382:microbiology; D015169:Colony Count, Microbial; D015925:Cryopreservation / Q000379:methods*; D004195:Disease Models, Animal; D005456:Fluorescent Dyes; D005990:Glycerol; D050296:Microbial Viability; D008828:Microbiological Techniques / Q000379:methods; D016881:Microsporidiosis / Q000382:microbiology / Q000662:veterinary; D016818:Nosema / Q000254:growth & development* / Q000472:pathogenicity*; D011419:Propidium; D013172:Spores, Fungal / Q000254:growth & development* / Q000302:isolation & purification / Q000472:pathogenicity*; D013696:Temperature; D014867:Water
D005456:Fluorescent Dyes; D014867:Water; D011419:Propidium; D005990:Glycerol
Apis mellifera; Cryopreservation; Nosema ceranae; Spore infectivity; Spore viability