Evaluation of a safranin-O-stained antigen microagglutination test for francisella tularensis antibodies

A microagglutination test for Francisella tularensis, with 0.025-ml amounts of diluted sera and 0.025-ml amounts of safranin-O-stained antigen in U-bottom microtitration plates, was compared with a tube agglutination test by using 137 sera. There was 86.3% agreement (+/- 1 dilution variation) between the microagglutination results and the tube agglutination results for sera with tube agglutination titers of greater than or equal to 20. There was 100% agreement (+/- 1 dilution variation) for sera with titers of less than 20. The advantages of the microagglutination test are: (i) it requires fewer man hours to perform; (ii) it requires only one-twentieth of the amount of antigen; and (iii) it is easier to read.