Persistence of Group A Streptococci Labeled with Fluorescein Isothiocyanate in Inflammatory Sites in the Heart and Muscle of Mice and Rabbits ∗

Summary

A simple method of labeling living group A streptococci with fluorescein isothiocyanate (FITC) is described. Low concentrations of FITC (10-50 μg/ml) labeled group A streptococci but affected neither the viability of the cells nor the capacity of the streptococci to produce acid from glucose or to form cell-bound streptolysin S. Mucopeptide prepared from group A streptococci by the formamide method and group A streptococcal L-forms were readily labeled with FITC. On the other hand C-polysaccharide could not be labeled with FITC when in solution. Group A streptococci, streptococcal cell debris, and mucopeptide labeled with FITC injected into the thigh muscle of mice and rabbits and intramyocardially into rabbits persisted intracellularly in histiocytes for several months. Since FITC-labeled group A L-forms, which are devoid of cell walls, disappeared from the site of injection within 24-72 hr it is suggested that the long persistence of streptococci and products in the tissues is probably due to the inability of the host enzymes to degrade cell-wall components of streptococci. The direct method of labeling streptococci and products with fluorescent material may prove useful to the study of host-parasite relationships.