Organisms conforming to "rhodochrous taxon" were isolated from three immunocompromised patients, suggesting a pathogenic role for the organisms. The organisms are partially acid-fast, grampositive catalase positive rods which form orange or red colonies aerobically in three or four days on Sabouraud, Mueller-Hinton and Middlebrook 7H-10 agars. They are differentiated from Nocardia by morphology and ability to degrade ethylene glycol in 7H-10 media. Two of these clinical isolates and a reference strain were injected intraperitoneally into guinea pigs, half of which received methylprednisolone intramuscularly beginning three days prior to inoculation. Steroid-treated animals exhibited clinical illness, diffuse peritonitis and recovery of inoculated organisms whereas one of three nonsteroid-treated animals exhibited a localized abscess without recovery of organisms. This study suggests that rhodochrous may be pathogenic under conditions of immune compromise.
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