The lysozyme test (indicating positive growth or negative growth) may be used to help in characterize aerobic actinomycetes.
Note: From the extent of the following (abbreviated) algorithm, it becomes apparent that phenotypic characterization takes a great deal of time and expertise in special bacteriology procedures. (Most medical laboratories no longer perform full phenotypic characterizations, opting instead for specialized molecular testing, which will be discussed in the next section.)
The following is an abbreviated representation of a lysozyme flowchart published by Saubolle, Mochon, and Sussland in Leber's "Clinical Microbiology Procedures Handbook"27(figure 6.3-1):
If the lysozyme is positive:
- Test on casein media for hydrolysis
- If casein is positive, test on adenine media for hydrolysis
- N. pseudobrasiliensis is adenine positive, while N. brasiliensis is adenine negative.
- If casein is negative, test on xanthine media.
- If xanthine is positive, look for aerial hyphae.
- No aerial hyphae and acetamide positive indicates T. tyrosinolsolvens
- Aerial hyphae indicate N. otitidiscaviarum
- If xanthine is negative, test on hypoxanthine media.
- If hypoxanthine is negative, look for aerial hyphae.
- Aerial hyphae and arylsulfatase positive indicate N. nova.
- Aerial hyphae and arylsulfatase negative indicate N. farcinia (growth in L-rhamnose) or N. abscessus, N. brevicatena, N.cyriacigeorgica, N. paucivorans (no growth in L-rhamnose)
If the lysozyme is negative:
- Test cell wall by adjunct methods for meso-DAP and L-DAP.
- I-DAP presenceindicates Streptomyces.
- meso-DAP presence indicates aerial hyphae must be observed to characterize as Nocardiopsis spp.
- A lack of aerial hyphae indicates testing for mycolic acids (MAS) is warranted.
- Rhodococcus and Gordonia contain mycolic acids
- Actinomadura does not contain mycolic acids
27. Leber AL, ed. Clinical microbiology procedures handbook. 4th ed. ASM Press; 2016:Section 6.
