1.4.3. Preservation of in vitro cultures
An A. apis isolate starts to show signs of aging after 30 days of growth (Ruffinengo et al., 2000) and thus requires monthly transfer. However, frequent culture transfers are expensive, time consuming and increase the risk of contamination. In addition, A. apis isolates, as seen for many other microbes, can lose virulence when kept in culture with repeated transfers, thus it is important to utilize a long term storage method soon after an isolate is obtained. Two different culture preservation methods have been successfully used: cryopreservation (Jensen et al., 2009a) and propagation on Integral Rice Kernels (IRK) (Palacio et al., 2007). Contamination during storage seems to be less risky during cryopreservation at -80°C, however for larger quantities and for laboratories not equipped with cryopreservation capacity, the use of rice kernels is a great alterative.