For detailed flowcharts and tables differentiating characteristics of Nocardia, Rhodococcus, Tsukamurella, and Gordonia, refer to section 6 of the Clinical Microbiology Procedures Handbook.13 Media and methods used for phenotypic characterization of the aerobic actinomycetes include:
- Acetamide hydrolysis medium: Color change from yellow-orange to deep pink when the enzyme acylamidase is present, deaminating acetamide and producing ammonia; used to differentiate between several Nocardia species
- Arylsulfatase liquid medium: Color changes to pink or red when the enzyme hydrolyzes the bond between sulfate and the aromatic ring in a compound. Arylsulfatase is used to differentiate rapidly growing Mycobacteria from several important Nocardia species.
- Carbohydrate basal medium: Gordon's oxidative slants; oxidative acid production of carbohydrates; color change from purple to yellow
- Carbohydrate utilization tests: Utilization of individual carbohydrates; may also include panels in commercial tests like API 20C AUX (Biomerieux), API 50 CH (Biomerieux), Biotype-100
- Citrate agar: Simmons; development of a dark blue color, which denotes alkalinization
- Decomposition of substrates: Ability or inability of the bacteria to hydrolyze adenine, casein, hypoxanthine, tyrosine, and xanthine
- Esculin hydrolysis medium: Esculin hydrolysis produces esculetin, which reacts with iron salt to produce a dark brown/black complex
- Lysozyme test: Determines the organism's ability to grow in the presence of the enzyme; good growth indicates resistance
- Nitrate reductase: Nitrate broth is used to determine the organism's ability to reduce the nitrate to nitrite, free nitrogen gas, or other reduced nitrogen compounds
- Urease: Determine an organism's ability to hydrolyze urea; a positive test is indicated by a bright pink color
- Susceptibility testing profile for ID only: abbreviated antimicrobial profile used to identify commonly seen Nocardia species by Kirby-Bauer or broth microdilution testing; used in conjunction with other tests
- Adjunct method: Chromatography to test cell wall for diaminopimelic acid (DAP) isomers meso- and L-DAP
