Nocardia brasiliensis characteristics, morphology, diseases

Charles McCarthy

The Nocardia brasiliensis It is a bacterium that belongs to the broad group of actimomycetes that is distributed throughout the entire geography of the planet. It is one of the best known human pathogens.

This bacterium has certain particular characteristics. On occasion it has been classified as gram positive, however it is also considered acid resistant. It also synthesizes a large number of enzymes that give it properties that allow it to be identified at an experimental level and differentiate it from other bacteria..

Nocardia. Source: Public Domain Files

Edond Nocard, a French veterinarian, was the one who first described a disease caused by bacteria of the genus Nocardia in a mammal. Later, the first description of a disease in humans was made, a brain abscess. Today it is known that Nocardia brasiliensis is the causative agent of most cases of Actinomycotic Mycetoma.

From there, there have been many studies that have been carried out on the pathogenic potential of these bacteria, especially the Nocardia brasiliensis. Knowing the most important aspects of the development of this bacterium is important because the pathology caused by it wreaks havoc on those who suffer from it..

Article index

  • 1 Taxonomy
  • 2 Morphology
  • 3 General characteristics
  • 4 Diseases
    • 4.1 Actinomycotic mycetoma
    • 4.2 Symptoms
    • 4.3 Diagnosis
  • 5 Treatment
  • 6 References


The taxonomic classification of this bacterium is as follows:

Domain: Bacterium

Edge: Actinobacteria

Order: Actinomycetales

Suborder: Corynebacterineae

Family: Nocardiaceae

Gender: Nocardia

Species: Nocardia brasiliensis.


Bacterial cells of Nocardia brasiliensis They are shaped like a thin rod, with a diameter of approximately 0.5-0.8 microns. Likewise, as a member of the actinomycetes, it manifests its characteristic structure with branches and sub-branches. There are no cilia or flagella. Nor is it surrounded by a capsule.

The cell wall is made up of mycolic acids, compounds that have between 36 and 66 carbon atoms. Likewise, other lipids are found in the layer, such as diaminopimelic acid, dysphosphatidyl glycerol, phosphatidylinositol and phosphatidylenatolamine, among others..

Once grown on artificial media, it is appreciated that the colonies give off a strong smell of damp earth, have a whitish, plaster-like color and ridges.

General characteristics

They are acid resistant

Due to the composition of its cell wall, specifically mycolic acids, this bacterium cannot be stained correctly through the Gram stain. This is because it is immune to the typical bleaching process, an essential part of staining techniques..

In contrast, the Nocardia brasiliensis stains with the Kinyoun method, widely used in bacteria of the genus Nocardia.

They are aerobic

The Nocardia brasiliensis it is a strictly aerobic bacterium. This means that in order to carry out its metabolic processes, it necessarily requires oxygen..

That is why in order to survive and develop properly, it must be in an environment with a sufficient proportion of this element..

They are catalases positive

The bacterium synthesizes the enzyme catalase, through which it is possible to unfold the hydrogen peroxide molecule (HtwoORtwo) in water and oxygen. This property is very useful when it comes to identifying unknown bacteria at an experimental level..

They are urease positive

The Nocardia brasiliensis synthesizes the enzyme urease. This is responsible for catalyzing the hydrolysis reaction of urea to obtain ammonium and carbon dioxide, according to the reaction:

CO (NHtwo)two + 2H+ + 2HtwoO - 2NH4+ + COtwo + HtwoOR


This bacterium is widely distributed throughout the planet, in a multitude of environments, mainly linked to the soil..

It is saprophytic, which implies that it is found on dead organic matter, contributing to its disintegration and decomposition..

It is positive casein

Bacterial cells of the Nocardia brasiliensis they synthesize the enzyme caseinase. This enzyme has the function of catalyzing the hydrolysis reaction of casein, a known protein present in milk.

When this test is performed, skim milk agar is used as the culture medium. The bacterial strain is seeded in the center and after approximately 10 days a transparent area is seen around the colony. This is an unequivocal sign that the bacteria are synthesizing the enzyme..

This constitutes another very useful test to differentiate some species of bacteria from others..

Growing conditions

This bacterium is mesophilic, having an optimal growth temperature located between 35 ° C and 37 ° C. Likewise, they require a slightly alkaline pH, being located in a range between 7.0 and 9.2. They also need an atmosphere that contains approximately 5-10% carbon dioxide..


This bacterium is mainly associated with skin pathologies, the most representative being Actinomycotic Mycetoma..

Actinomycotic mycetoma

It is a pathology of progressive development that initially affects the skin and subcutaneous tissue, but later it can invade muscle tissue and even bones.

Its incidence is particularly high in areas near the Tropic of Cancer, as well as being significantly higher in men. Most of the reported cases involve individuals whose ages are between 20 and 45 years of age..

The body site in which it manifests itself in most cases is in the lower limbs, followed in frequency by the legs, upper limbs, trunk and head..

The incubation period is variable, it can range from weeks to months.


The first symptom is a small tumor-like lesion, firm and hard to the touch, as well as adherent. It is usually located in the place where there was previously an injury or injury, which must have been in contact with the ground.

Later, the lesion softens and a purulent material begins to ooze. Over time, more nodules begin to appear, joining the initial lesion.

Mycetoma. Source: By haitham alfalah (Halfalah (talk) 13:20, 24 July 2008 (UTC)) [CC BY-SA 3.0 (], via Wikimedia Commons

Finally, a large, woody-like tumor forms, with numerous fistulas through which purulent or bloody material drains. Some of the holes are covered by scabs.

The fistulas reach different depths, being able to affect deep planes in the underlying tissues. In general, the lesions do not present pain. This appears already when the injuries have advanced in severity.

The deformity of the area is clear evidence of the advancement of the pathology.


The specialist doctor, in this case, the dermatologist, is able to recognize the lesions with the naked eye. However, you need to run some tests to arrive at a sure diagnosis..

A sample of the purulent discharge and affected tissue should be taken for culture to fully identify the causative agent..


The treatment for this pathology can be of two types: medicinal and surgical. 

Regarding the drugs to be administered, the scheme to be followed must be decided by the specialist doctor..

The most commonly used antibiotics to treat this condition are: trimetropin, sulfamethoxasol, and amikacin. They are generally given in combination therapy.

Surgical debridement is necessary in cases where the infection has advanced to the bone. In the most critical cases, even the amputation of the affected limb has been required to prevent the spread of the infection..


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  2. Hernández, P., Mayorga, J. and Pérez, E. (2010). Actinomycetoma by Nocardia brasiliensis. Annals of Pediatrics. 73 (4). 159-228
  3. Nocardia brasiliensis. Retrieved from:
  4. Salinas, M. (2000). Nocardia basiliensis: from microbe to human and experimental infections. Microbes and infections. 1373-1381
  5. Serrano, J. and Sandoval, A. (2003). The mycetoma: Review. Journal of the Venezuelan Society of Microbiology. 23 (1).
  6. Spelman, D. Microbology, epidemiology and pathogenesis of nocardiosis. Retrieved from:
  7. Villarreal, H., Vera, L., Valero, P. and Salinas, M. (2012). Nocardia brasiliensis Cell Wall Lipids Modulate Macrophage and Dendritic Responses That Favor Development of Experimental Actinomycetoma in BALB / c Mice. Infection and Immunity. 80 (10). 3587-3601.

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