Phenotypic and Molecular Identification of Nocardia in Brain Abscess.

Sir,

Shirani et al. recently reported an article entitled, “Nocardial brain abscess in a patient with pulmonary alveolar proteinosis” (DOI: 10.4103/2277-9175.164004).[1] The genus Nocardia is a Gram-positive aerobic, partially acid-fast, and filamentous bacterium that causes nocardial infections (nocardiosis) in human. The genus Nocardia is normal microflora in the environment such as soil and dust.[2] Nocardiosis treatment is different in various species, and some species are resistant to different antibiotics such as trimethoprim-sulfamethoxazole, carbapenem, and aminoglycosides, as well as accurate identification in species level is important.

Attention to comments and questions:

Isolation and characterization of morphology of colony, aerial hyphae, Gram stain, partially acid-fast, acid-fast, growth in lysozyme broth and molecular methods are important for the genus Nocardia confirmation.[234] Moreover, other aerobic actinomycetes such as Gordonia spp., Rhodococcus spp., and Tsukamurella spp. are Gram-positive, may be filamentous and colonial morphology are similar to each other. Gordonia spp., Rhodococcus spp., Tsukamurella spp., and Nocardia spp. are acid-fast in under certain conditions (bacteria listed are partially acid-fast and normally are not positive for acid-fast staining)[23456789101112] while authors suggested that branching, filamentous, Gram-positive, and acid-fast positive elements are the genus Nocardia

Authors reported Nocardia asteroides identification with culture and staining.[1] Phenotypic methods such as hydrolysis of amino acids, production of nitrate reductase, gelatinase, and urease, producing acid from carbohydrates, and growth at 45°C[2] are used in species level identification. I have two questions for authors:

The genus Nocardia has some of complex groups such as N. asteroides complex (N. asteroides, Nocardia cyriacigeorgica, Nocardia farcinica, etc.,) and Nocardia nova complex.[2] Authors explain that how identified N. asteroides of other species in N. asteroides complex?

The authors have not mentioned of the use of molecular techniques to Nocardia identification at species level in the article. The authors explain molecular method if used.

In literature, although phenotypic methods are labor intensive and time-consuming, they are used in combination with molecular techniques such as polymerase chain reaction (PCR) sequencing (16S rRNA, hsp65, rpoB, gyrB, and secA genes) and PCR-restriction fragment length polymorphism for accurate identification in genus and species levels for Nocardia[213]

Drug choice for nocardiosis treatment is co-trimoxazole, but some of species are resistance to co-trimoxazole and other antibacterial agents; therefore, accurate identification in species level and antimicrobial susceptibility testing are important.[214] Further, in literature, some of patients have hypersensitive reaction to co-trimoxazole.[15]

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