An ultrastructural comparison of the cell envelopes of selected strains of Nocardia asteroides and Nocardia brasiliensis.

Growth curves were determined for three strains each of Nocardia asteroides and Nocardia brasiliensis. Two strains of N. brasiliensis and one strain of N. asteroides had longer lag periods of growth than the remaining three strains. All strains had generation times of approximately 5.5 hours. The ultrastructure of the cell envelope of each Nocardia strain in early stationary phase growth was also examined. All the strains had typical trilaminar cell walls and cell membranes. The thickness of the cell wall layers, especially the inner peptidoglycan layer, varied from strain to strain. The inner layer of two strains of N. brasiliensis and one strain of N. asteroides was 12 nm or more in thickness, while that of the remaining three strains was 7 nm thick. These observed differences in growth patterns and/or thickness of the cell wall layers could be correlated to the varying degrees of virulence as well as the divergent pathologies exhibited by these organisms.