Williamsia is similar to Rhodococcus and Gordonia, and is rarely associated with human disease.
Nine species have been known to cause human infections.
Note: Images are scarce, but a good source for the workbench is the Manual of Clinical Microbiology (published by ASM Press).
| Characteristics | Comments |
| Appearance on Gram stain | Short gram-positive rods or coccobacilli; not branching |
Appearance on modified acid-fast stain
| Not acid-fast |
Most often associated with clinical disease57
| W. muralus associated with pulmonary and endopthalmitis. W. serinedens has been associated with perinatal sepsis. |
| Colonial growth | Smooth, yellow to orange (or red) colonies |
| Phenotypic characterization | Not helpful; use molecular testing such as 16S rRNA gene sequencing |
| Temperature of optimal growth | 10 - 37°C |
57. Conville PS, Brown-Elliott BA, Witebsky FG. Nocardia, Rhodococcus, Gordonia, Actinomadura, Streptomyces, and other aerobic actinomycetes. In: Carroll KC, Pfaller MA, Landry ML, McAdam AJ, Patel R, Richter SS, Warnock DW, eds. Manual of Clinical Microbiology, 12th ed. ASM Press; 2019:525-557.
