Ultrastructural, physiological, and cytochemical characterization of cores in group D streptococci

Cores are large, rod-shaped structures that have been found almost exclusively in group D streptococci, measure 0.1 to 0.16 mum in diameter, and extend the width or length of cells. This study has shown that cores are produced in the cells at a reproducible point in early stationary growth after extensive mesosomal formation and after the pH has dropped below 6.5. When cells containing cores were introduced into a fresh medium with a pH above 6.5, the structures disappeared within 5 min. The structures were not found in young, logarithmically growing cells but formed in these cells upon autolysis or treatment with penicillin. Cores that were forming or disintegrating appeared to have a lamellar substructure. When chloramphenicol was added to the medium before the culture reached stationary phase, no cores were found in the cells. Cytochemical studies indicated that cores contain protein and are not composed of cell wall material or other polysaccharides that contain 1,2-glycol groups.