A further refinement is the fluorescent antibody technique. Rabbits are injected with pure cultures of B. larvae and the antiserum is conjugated with a fluorochrome dye. The resulting fluorescent antibody is reacted with a bacterial smear on a slide. Any excess anti-serum is washed off and the smear is examined by fluorescence microscopy. To culture B. larvae , spore suspensions are prepared by mixing diseased material in 9 ml of sterile water in test tubes.
Individual colonies are small and opaque.
If the inoculum contains large numbers of spores, a solid layer of growth will cover the plate. This test should be used for confirmation and should not be employed alone. Occasionally, it may be necessary to examine honey for the presence of B. larvae . The open end is tied after filling. The tubes are submerged in running water for 18 hours or in a water bath with 3-4 water changes over the same time period.