The Opsonification Test for the Rapid Identification of the Streptococcus of Scarlet Fever

Abstract

The opsonification test described by Tunnicliff 1 for the rapid identification of the streptococcus of scarlet fever has been tried with a number of streptococci isolated from patients with scarlet fever and from patients with a variety of other diseases, in order to study further the efficiency of the test in the diagnosis of scarlet fever. The opsonic technic used in the test was the modified method employed by Tunnicliff. The phagocytic leukocytes were obtained by mixing equal parts of normal human blood and 2% sodium citrate in physiologic salt solution. The streptococci under examination were either picked directly from the first blood agar plate or from subcultures on blood agar slants, and were suspended in physiologic salt solution. The serums used in the test were serum of horse immunized against scarlet fever streptococcus, and normal horse serum. Equal parts of serum, citrated blood, and streptococcus suspension were mixed in capillary pipets and incubated 25 minutes at 36 C. Each mixture was smeared on a glass slide and stained with Wright's blood stain; 50 polymorphonuclear leukocytes were counted, and the number taking part in phagocytosis was noted (nhagocytic index). The phagocytic index of the immune serum divided by the phagocytic index of the normal serum constituted the opsonic index. A high opsonic index would indicate that the streptococcus under examination was probably of scarlatinal origin, and a low index would indicate that the strain of streptococcus was nonscarlatinal. Certain difficulties arose from time to time in the performance of the opsonification tests. One immune serum had a tendency to agglutinate the citrated blood that was ordinarily used in the test. Whenever it was necessary to use new serum, a preliminary test was made mixing equal parts of serum and citrated blood and incubating the mixture. If agglutination resulted, the citrated blood of this person was not used again. A few of the cultures that grew with difficulty