Natural Resistance of Germ-Free Mice and Colostrum-Deprived Piglets to Group A Streptococci

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Abstract
Summary: A study was made of the resistance of germfree and conventional mice to direct challenge with Group A streptococci of graded virulence. Germ-free and conventional mice were highly, and equally, resistant to nonencapsulated strains of Group A streptococci lacking M protein. Greater susceptibility of germ-free mice could be demonstrated only with Group A strains containing both M protein and capsules. This difference could be abolished by a globulin fraction of normal mouse serum but not by normal mouse γ-globulin or by homologous type-specific antiserum. In vitro studies with bloods of germ-free mice and colostrum-deprived piglets provided additional evidence that phagocytosis of avirulent Group A streptococci required little, if any, specific antibodies. Bloods from these animals phagocytized and destroyed streptococci as readily as did their conventional counterparts. Thermolabile opsonins against avirulent Group A streptococci were readily demonstrable in the blood of colostrum-deprived piglets, whose serum contains only minute amounts of γ-globulin. Absorption of the sera of these animals at low temperatures with large amounts of homologous streptococci resulted in some decrease in opsonization, but considerable residual phagocytosis was apparent. The leukocytes of colostrum-deprived, and of colostrum-fed, animals were equally capable of phagocytizing and destroying Group A streptococci in the presence or absence of specific opsonins.