Test procedure
i) The antigen is an aqueous extract of bacteria from which lipid has been removed (strain
M. paratuberculosis 316F). Mycobacterium avium D9 may also be used.
ii) All sera are inactivated in the water bath at 60°C for 30 minutes and diluted at 1/4, 1/8 and
1/16. A positive control serum and a negative control serum should be included on each
plate. The following controls are also prepared: antigen control, complement control and
haemolytic system control.
iii) Reconstituted, freeze-dried complement is diluted to contain six times H50 (50%
haemolysing dose) as calculated by titration against the antigen.
iv) Sheep erythrocytes, 2.5%, are sensitised with 2 units of H100 haemolysin.
v) All dilutions and reagents are prepared in calcium/magnesium veronal buffer; 25 µl
volumes of each reagent are used in 96-well round-bottom microtitration plates.
vi) Primary incubation is at 4°C overnight and secondary incubation is at 37°C for 30 minutes.
vii) Reading and interpreting the results: Plates may be left to settle or centrifuged and read as
follows: 4+ = 100% fixation, 3+ = 75% fixation, 2+ = 50% fixation, 1+ = 25% fixation and
0 = complete haemolysis. The titre of test sera is given as the reciprocal of the highest
dilution of serum giving 50% fixation. A reaction of 2+ at 1/8 is regarded as positive.
Results should be interpreted in relation to clinical signs and other laboratory findings.