Cores, Microbial Organelles Possibly Specific to Group D Streptococci

Abstract

A long, thin, approximately cylindrical core spans the interior of cells of 24-hr cultures of all group D streptococci that were examined, five strains of Streptococcus faecalis , single strains of S. faecalis subsp. zymogenes and S. durans , and three strains of Streptococcus spp. In one strain of S. faecalis , serial section electron microscopy showed that most cells possess a core. The core is 0.10 to 0.16 μm thick and consists of a matrix and an axial array of ribosomelike particles. It resembles one of two types of cores present in a stable protoplast form of one of the S. faecalis strains. Cores were not present in single strains of S. pyogenes (β-hemolytic group A), S. agalactiae (group B), S. dysgalactiae (group C), S. equisimilis (group C), and S. mitis (viridans group) that were examined; nor were cores observed in single strains of Staphylococcus aureus, Escherichia coli , and Bacillus megaterium . Cores may be useful, therefore, in identification of group D streptococci. For preservation and rapid recognition of cores, a glutaraldehyde-osmium tetroxide sequence of fixation appears superior to the osmium tetroxide method often employed in processing bacteria for electron microscopy.