An ultrastructural analysis of Nocardia during experimental infections in mice.

Several strains of Nocardia that varied from virulent to avirulent were injected intraperitoneally into young mice. Histological and ultrastructural analysis of the resultant infections revealed that the bacteria and the lesions they induced were different depending upon the strain of organism used. Further, the morphological and tinctorial characteristics of the bacteria grown in vitro changes during growth in vivo. These observations strongly suggested that chemical and physical alterations occurred in the cell envelope of the Nocardia when grown in mice. Electron microscopy confirmed that significant structural modification occurred, especially in the cell envelope, when the nocardial cells established themselves within the host tissue. It was shown that the least virulent strain exhibited the most dramatic changes whereas the most virulent organism appeared to be affected the least.