Mycobacterium genavense" is a proposed new species recently reported to cause disseminated infections in 18 patients with AIDS in Europe. We have recovered "M. genavense" as slowly growing fastidious mycobacteria in blood cultures of seven patients with AIDS. In the original studies of "M. genavense," the fastidious organism grew only in BACTEC 13A vials. The Seattle, Washington, isolates of "M. genavense" also failed to grow when subcultured from 13A vials to routine solid media, but dysgonic colonies were produced on Middlebrook 7H11 agar supplemented with mycobactin J. The mycolic acid pattern of patients' isolates closely resembled that of the type strain of Mycobacterium simiae when analyzed by one-and two-dimensional thin-layer chromatography and by high-performance liquid chromatography. Whole-cell fatty acid analyses by gas-liquid chromatography distinguished the isolates from M. simiae but misidentified them as Mycobacterium fortuitum. Sequence determinations of the hypervariable regions of the 16S rRNA gene indicate that these organisms belong to the recently proposed new species "M. genavense." Growth from Middlebrook 7H11 agar supplemented with mycobactin J consistently yielded positive tests for catalase (semiquantitative and at 68°C), pyrazinamidase, and urease which enable mycobacteriology laboratories to presumptively identify "M. genavense" without nucleic acid analyses. The failure of "M. genavense" to grow on conventional mycobacterial solid media suggests that mycobacterial blood cultures should include a broth medium incubated for at least 8 weeks.

During a 14-month period, a unique strain of Corynebacteyium striatum that produces a diffusible brown pigment was isolated from purulent sputa of nine patients and from nonrespiratoxy sites of two additional patients. Seven nonpigmented clinical isolates from the same period and three reference strains of C. striatum were compared with the brown isolates. Most patients had multiple sputum cultures with no coryneforms before the brown strain emerged, suggesting that the organism was hospital acquired. DNA restriction fragment patterns and Southern hybridization with the att site probe of Corynebacterium diphtheriae indicated that the brown isolates were a single strain which was distinct from the heterogeneous nonpigmented strains. A common source for the brown C. striatum was not recognized, although all of these patients were located in two adjoining intensive care units. All of the brown isolates, three of the nonpigmented clinical isolates, and two reference strains had positive CAMP reactions with Staphylococcus aureus, which has not been reported for C. striatum prior to this study.

Antibiotic-resistant Corynebacterium strains were isolated from 14 Harborview and one Veterans Administration Hospital patients in Seattle during the period 1987-90. These clindamycin-erythromycin resistant strains were shown to hybridize with the ermCd gene, which was cloned from a Corynebacterium diphtheriae plasmid and encodes for a rRNA methylase. Thirteen of these strains also hybridized with the tetM gene probes, and were tetracycline resistant. The ermCd gene could be transferred, by conjugation, while the tetM gene was not transferable.