Nutritionally deficient streptococci: electron microscopic study of 14 strains isolated in bacterial endocarditis.

Fourteen strains of nutritionally deficient streptococci were isolated from patients with bacterial endocarditis and observed by light and electron microscopy. In brain-heart infusion broth supplemented wit Isovitalex, they could be distributed into three morphological groups in which numerous abnormalities involving septation or cell wall structure were showed. Group I (strains 7, 8, 13, 14) was characterized by coccobacilli resulting from failure of cross wall formation between two cocci. Cell wall structure was normal. Group II (strains 2, 4, 5, 11, 12) was characterized by long chains of elongated bacteria (rod-shaped bacteria) resulting from failure of cross wall formation and failure of separation of daughter cells after division; cell wall structure was normal. Group III (strains 1, 3, 6, 9, 10) was characterized by different abnormalities of cell wall thickness and structure. The cell wall was irregularly enlarged (strains 9, 10), thick and stratified (strain 1), or desquamating (strains 3, 6). These abnormalities of septation with or without abnormalities of cell wall appear to be much more important than those observed on normal streptococci during unbalanced growth in deprived media. They can be compared to the abnormalities shown in vivo by the bacteria of the dental plaque. The differences observed between the strains might be due to different metabolic deficiencies.