For detailed flowcharts and tables differentiating characteristics of Nocardia, Rhodococcus, Tsukamurella, and Gordonia, refer to section 6 of the Clinical Microbiology Procedures Handbook25; according to Leber, 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 - API 20C AUX [Biomerieux], API 50 CH [Biomerieux], Biotype-100)
- Citrate agar (Simmons: development of a dark blue color, denotes alkalinization)
- Decomposition of substrates - the ability or inability of the bacteria to hydrolyze the following:
Adenine
Casein
Hypoxanthine
Tyrosine
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 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.
25. Leber AL, ed. Clinical microbiology procedures handbook. 4th ed. ASM Press; 2016:Section 6.
