Fifty-seven clinical isolates of previously unidentified gram-positive, fermentative, nonsporeforming rods were studied and compared to the type strains of Oerskouia turbata and 0 . xanthineolytica. Thirty-five of the isolates were identified as Oerskouia species: 9 were identified as 0. turbata, and 26 were identified as 0. xanthineolytica. The Oerskouia cultures could be differentiated from the other isolates on the basis of the development of filamentous colonies. The genus Oerskouia, described by Prauser et al. (€9, Sukapure et al. (ll), and emended by Lechevalier (61, consists of yellow-pigmented organisms with branched hyphae. These hyphae break up into motile, rodlike elements that "appear bacterial" in smears. These rods are gram positive and non-acid fast. Previously described sources of the organisms are soil, aluminum hydroxide gel antacid, and dry grass cuttings (6). During the last 20 years, the Special Bacteriology Section (SBS), Bacteriology Division, Center for Disease Control (CDC), has received for identification a number of motile, gram-positive, nonsporeforming, yellow pigment-producing organisms isolated from clinical sources. These organisms were not recognized as belonging to any established species and were arbitrarily designated as group A Corynebacterium sp. Later, this group was divided into five subgroups, primarily on the basis of carbohydrate reactions. When these isolates were observed to have characteristics similar to those reported for the genus Oerskovia, a collaborative study between the Actinomycete Laboratory of CDC's Mycology Division and the SBS was initiated to further characterize and classify them. Listeria denitrificans was included in this study because two of our colleagues, D. Hollis and G. Wiggins, had noted during earlier work on the genus Listeria that many biochemical characteristics of this species were similar to those of the group A strains.
A simple timesaving method for determining drug susceptibilities in vitro of isolates of Nocardia and Actinomadura is reported. An isolate is considered "susceptible" when the quantity of drug required for inhibition of growth is that concentration which might be obtained in serum by conventional therapy. Sulfonamides remain the drugs of choice for treating disease due to Nocardia species. Although doxycycline and minocycline appear to be very effective against Nocardia species, susceptibility testing may be desirable when a physician is considering substitution of an antibiotic for a sulfonamide. Susceptibility testing also may be desired before a drug is selected for treating disease due to Actinomadura madurae.
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