Culture conditions for the exclusive development of the mycelial and the yeast forms of Sporothrix schenckii from conidia in a rich, defined medium were established. Only the mycelial morphology developed when the pH of the medium was adjusted between 4.0 and 5.0 and the conidia were incubated at 25 degrees C, regardless of aeration. When the pH of the medium was adjusted between 6.5 and 8.0 and the conidia were incubated with aeration at 35 degrees C, only the yeast form was obtained. Using these culture conditions conidia were inoculated in a buffered-salts medium with vitamins with or without added carbohydrates as carbon sources. After incubation, the form obtained was recorded and the amount of growth determined on a dry weight basis. Development of the mycelial form was observed with all of the carbon sources tested (glucose, fructose, mannose, arabinose, maltose, sucrose and starch) while the yeast form developed only when glucose or another hexose was added to the medium. These observations indicated that in S. schenckii the development of conidia into a specific form is dependent on the interrelationship between the available nutrients and the culture conditions and that no specific parameter seemed to be exclusively determinant of the morphology obtained.
A dengue-2 live virus vaccine was tested in monkeys immune to heterologous dengue serotypes to determine if, as with wild DEN-2 virus, antibody-enhanced viraemia and seroconversion would occur. A low dose of 900 plaque-forming units (PFU) of the DEN-2/S-1 vaccine virus was inoculated subcutaneously into rhesus monkeys six months after they had received wild DEN-1, DEN-2 or DEN-3 viruses, and into non-immune monkeys. As previously reported for non-immune monkeys, there was little, if any, detectable vaccine viraemia in any of the groups of monkeys. There was no difference in seroconversion between the dengue heterologously immune (3/6) and non-immune (1/3) monkeys. These data indicated that (i) the vaccine virus may differ from the parent virus in the ability to complex with heterologous antibody and, thus, in the ability to infect Fc receptor bearing cells in monkeys; (ii) 10(3) PFU of vaccine virus is approximately the 50% infectious dose in monkeys as measured by seroconversion.
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