Experimental studies on the initial focus of invasion of group A streptococci.

Rabbits were infected with group A streptococci type 12 by an aerosol method, that seems to resemble closely the human natural infection, in order to investigate the mechanism of invasion, especially the initial focus of invasion of streptococci. Living streptococci and FITC-labelled streptococci were exposed to several groups of rabbits, which were sacrificed and divided according to the duration after exposure. The specimens of organs were examined by light microscopy, fluorescent microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Histologically, the adherence of streptocossi was found on the pharyngeal mucosa and tonsils and the mucocilial clearance in the larynx and the trachea. Phagocytosis was also found in the bronchus and lung. By SEM, invading streptococci and cell debris-like masses were observed in the micropore of the tonsillar crypt of the rabbit. From these results it was supposed that there should be differences of tissue tropisms and defence mechanisms against streptococci among the mucosa and that micropores of the tonsillar crypts should play an important role in the initial focus of invasion of group A streptococci.