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Bacilos Gram-positivos

Nocardia brasiliensis

Branching, beaded, filamentous Gram-positive bacilli

Identification & Growth

Identification

  • Partially acid-fast (modified Kinyoun)
  • Hydrolyses casein and tyrosine (xanthine negative)

Growth Conditions

  • Dry adherent colonies in 3–7 days; use Sabouraud and BHI in addition to blood agar

Clinical Significance

  • Actinomycotic mycetoma and cutaneous/lymphocutaneous infection after trauma

Intrinsic Resistance

  • Species-dependent profile; trimethoprim-sulfamethoxazole is the reference therapy

Bench Alerts

  • EUCAST/BrCAST do not define disk diffusion: test by broth microdilution (CLSI M62)
  • Warn the laboratory to extend incubation when clinically suspected

Clinical Notes

Clinical presentations

  • Leading agent of cutaneous actinomycetoma in tropical regions, with nodules, sinus tracts, and grain formation.
  • Can cause lymphocutaneous (sporotrichoid) infection after traumatic inoculation.
  • Systemic dissemination with pulmonary or central nervous system involvement is rarer than with other Nocardia species.

Specimens and collection

  • Purulent discharge grains from the mycetoma should be collected and examined macro- and microscopically.
  • Deep tissue biopsy is preferable to superficial swab to increase culture yield.
  • Culture should be maintained for a prolonged period (up to 2–4 weeks) on selective media, given slow growth.

Epidemiology and at-risk populations

  • Found in soil and decaying plant matter, especially in tropical and subtropical regions.
  • Rural and agricultural workers who sustain trauma from thorns or wood splinters have increased risk.
  • Brazil is a recognized endemic area for N. brasiliensis mycetoma.

Resistance and therapeutic implications

  • Trimethoprim-sulfamethoxazole is the first-line treatment, generally active against this species.
  • Prolonged treatment for months to years is required due to the chronic nature of the infection.
  • Susceptibility testing is recommended, as the susceptibility pattern varies among Nocardia species.

Bench and reporting notes

  • Branching, Gram-positive, partially acid-fast bacillus on modified Kinyoun stain.
  • Species identification by 16S rRNA or hsp65 gene sequencing is required, as phenotypic identification is limited.
  • White-yellow grains in mycetoma discharge are a characteristic macroscopic finding to be described in the report.

Sources

Educational decision-support content. It does not replace laboratory validation, current guidelines or review by the responsible professional.

FAQ: Frequently Asked Questions

How to identify Nocardia brasiliensis in the lab?

Nocardia brasiliensis is identified through partially acid-fast (modified kinyoun), hydrolyses casein and tyrosine (xanthine negative).

What are the intrinsic resistances of Nocardia brasiliensis?

This organism is naturally resistant to species-dependent profile; trimethoprim-sulfamethoxazole is the reference therapy. These drugs should not be reported as susceptible.

Where is Nocardia brasiliensis commonly found?

It is typically associated with actinomycotic mycetoma and cutaneous/lymphocutaneous infection after trauma.

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