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J Bacteriol. 1969 October; 100(1): 505-511
Copyright © 1969 American Society for Microbiology. All Rights Reserved.

Electron Microscopic Studies on Opaque Colony Variants of Group A Streptococci

^a Department of Microbiology, College of Physicians & Surgeons, Columbia University 10032
The Rockefeller University, New York, New York 10021

ABSTRACT

Opaque colony variants of two strains of group A streptococci have been compared with blue colonies of the same strains by electron microscopy. In opaque colonies, the cocci are joined into elongated chains by exaggerated intercellular septa that often occupy the major portion of each cell's circumference. The thickness and lamination of cell walls in opaque colony variants are identical to those aspects of cell walls in blue colony forms. The similarity in cell wall architecture is found between opaque and blue forms whether or not M protein (and M associated surface fimbriae) is present. Extensive, direct contact between the nucleoid and the cytoplasmic membrane beneath intercellular septa is seen in opaque colony variants. The relationship of this marked nucleoid-cytoplasmic membrane association to the unusual chain forms in the opaque colony variants is unclear.

¹ Present address: Dept. Microbiology, Mount Sinai School of Medicine, 10 East 102nd Street, New York, N.Y. 10029.

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