Variation in Lipid Content of Strains of Histoplasma capsulatum Exhibiting Different Virulence Properties for Mice

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Abstract
Nielsen , H. S., Jr. (Duke University Medical Center, Durham, N.C.). Variation in lipid content of strains of Histoplasma capsulatum exhibiting different virulence properties for mice. J. Bacteriol. 91: 273–277. 1966.—Lipid content and virulence were studied in six isolates of Histoplasma capsulatum in an attempt to determine whether or not the two factors could be correlated in this fungus. Virulence was evaluated by injecting dba line 1 male mice intracerebrally with 2.8 × 10 4 infective yeast-phase units and recording organ involvement and spontaneous deaths occurring in a 20-day period. Yeast cells were extracted with mixtures of ethyl alcohol-diethyl ether (3:1, v/v), and the total extractable lipid, as determined by solubility in petroleum ether, was separated into acetone-soluble and phospholipid fractions by acetone precipitation. Neutral lipids were measured directly by weighing, whereas total phospholipids were calculated after the colorimetric determination of phosphorus. The mixed phosphatides of two isolates, differing in virulence, were separated into five fractions by use of a column of silicic acid and Hyflo Super-Cel. In the six isolates studied, neither total extractable lipid, acetone-soluble lipid, nor phospholipid showed a quantitative correlation with virulence. Phosphatidylserine, cephalin, phosphoinositides, and sphingolipids were present in essentially the same amounts in the two strains investigated; however, a lecithin fraction was absent in the less virulent form. These data suggest that the quantity of phosphatidylcholine demonstrated for a given isolate of H. capsulatum may provide some insight as to its virulence, although such a relationship is lacking for total lipid, the acetone-soluble fraction, and the combined phospholipids of yeast-phase growth.