Bacilos Gram-positivos

Nocardia spp.

Filamentous, branching Gram-positive bacilli

Identification & Growth

Identification

Partially acid-fast (positive with modified Kinyoun stain)
Catalase-positive, strict aerobe; species identification by MALDI-TOF or sequencing

Growth Conditions

Grows slowly (3–14 days) on blood agar, Sabouraud agar and BCYE agar
Dry, adherent colonies with an earthy odour; notify the laboratory to extend incubation

Clinical Significance

Pneumonia in immunosuppressed patients, brain abscess, cutaneous mycetoma

Intrinsic Resistance

Susceptibility pattern varies by species — do not presume; send to a reference laboratory

Bench Alerts

Trimethoprim-sulfamethoxazole is the backbone of treatment
Respiratory isolation in an immunosuppressed patient warrants CNS investigation

Clinical Notes

Clinical presentations

Subacute to chronic cavitary pneumonia, often mistaken for tuberculosis, is the most common pulmonary presentation.
Hematogenous dissemination can cause multiple brain abscesses, especially in immunocompromised hosts.
Actinomycotic mycetoma (primary cutaneous nocardiosis) occurs after traumatic inoculation with sinus tract formation and grains.
Sporotrichoid lymphocutaneous infection is also described after trauma with soil-contaminated material.

Specimens and collection

Sputum, bronchoalveolar lavage and lung biopsies should be processed with modified Kinyoun stain for partially acid-fast bacilli.
Prolonged culture (up to 2-3 weeks) on both nonselective and selective media is necessary due to slow growth.
Brain abscess material should be sent for culture and histopathology when neuroimaging suggests focal lesion.

Epidemiology and at-risk populations

Found in soil and decaying organic matter; infection occurs via inhalation or traumatic inoculation.
Transplant recipients, chronic corticosteroid users and patients with advanced HIV have increased risk of disseminated disease.
Prior structural lung disease, such as bronchiectasis, predisposes to pulmonary colonization and infection.

Resistance and therapeutic implications

Species-level identification is important because susceptibility profiles vary significantly among Nocardia species.
Trimethoprim-sulfamethoxazole is historically the agent of choice, but resistance has been reported in some species.
Broth microdilution susceptibility testing is recommended to guide prolonged therapy, especially in disseminated disease.

Bench and reporting notes

Colonies with an earthy odor and thin branching aerial hyphae resemble filamentous fungi, but Gram stain reveals branching Gram-positive filamentous rods.
Weak positivity on modified acid-fast staining helps differentiate from Actinomyces, which is acid-fast negative.
Referral to a reference laboratory or molecular identification (16S rRNA sequencing) is recommended for definitive species identification.

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 spp. in the lab?

Nocardia spp. is identified through partially acid-fast (positive with modified kinyoun stain), catalase-positive, strict aerobe; species identification by maldi-tof or sequencing.

What are the intrinsic resistances of Nocardia spp.?

This organism is naturally resistant to susceptibility pattern varies by species — do not presume; send to a reference laboratory. These drugs should not be reported as susceptible.

Where is Nocardia spp. commonly found?

It is typically associated with pneumonia in immunosuppressed patients, brain abscess, cutaneous mycetoma.

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