Nocardia asterroids characteristics, morphology, diseases

David Holt

Nocardia asteroides it is a strict aerobic bacteria, catalase positive that is widely distributed on the planet. It has been isolated from a multitude of environments, because its development requirements are not so demanding.

The genus Nocardia was discovered by Edmond Nocard, with Nocardia asteroides being one of the species that make it up. These bacteria are considered to be weak Gram positive and partially acid-alcohol resistant..

Nocardia asteroides. Source: By Image credit: CDC / Dr. David Berd (PHIL # 3078), 1972. [Public domain], via Wikimedia Commons

This bacterium is a known human pathogen, although its infections are increasingly rare, being almost relegated to people with affected immune systems. An example of these are people with HIV, with leukemia or transplants, among others.

Of all the pathologies that it can generate, pulmonary nocardiosis is the most common, while the most infrequent are extrapulmonary, such as keratitis or endophthalmitis. Prevention and treatment against this bacterium are important, since the consequences of late diagnosis can be lethal.

Article index

  • 1 Taxonomy
  • 2 Morphology
  • 3 General characteristics
  • 4 Diseases
    • 4.1 Pulmonary nocardiosis
    • 4.2 Primary cutaneous nocardiosis
    • 4.3 Keratitis
    • 4.4 Endophthalmitis
  • 5 Treatment
  • 6 References


The taxonomic classification of Nocardia asteroides is as follows:

Domain: Bacterium

Edge: Actinobacteria

Order: Actinomycetales

Suborder: Corynebacterineae

Family: Nocardiaceae

Gender: Nocardia

Species: Nocardia asteroides,


Bacterial cells of Nocardia asteroides They are shaped like bacilli with a diameter of approximately 0.5 to 1 micron. The distinctive feature of these bacilli is that they are branched and have right-angle subbranches. The bacteria are not surrounded by a capsule. There is also no presence of cilia or flagella.

In the cultures, colonies of variable appearance are appreciated, with a characteristic smell of humid earth and can be seen as white as chalk, brown pink or salmon.

The bacterium has a type IV cell wall, composed of peptidoglycan. It also has saturated mycolic acids, arabinose, galactose and 2,6 meso-diaminopimelic acid..

General characteristics

It is saprophytic

This bacteria is found on dead organic matter. It constitutes a fundamental element in the decomposition of organic matter, contributing to the fragmentation of large molecules into smaller ones that become part of the nutrients in the soil..

It's acidic - alcohol resistant

Because one of the components of its cell wall is mycolic acids, this bacterium cannot be stained effectively through the Gram method..

The vast majority of experimental staining processes involve bleaching that is carried out by acidic substances or alcohols. In the case of bacteria such as Nocardia asteroides, there is resistance to this discoloration because mycolic acids do not allow the passage of these substances.

Despite this, there are methods that allow its coloring. Specifically the Nocardia astroides is colored through the Kinyoun method. In this, carbol fuchsin is used as a dye and methylene blue as a contrast..

She is strict aerobic

Like all living beings, Nocardia asteroides You must perform certain metabolic processes to obtain energy. For these processes requires mandatory oxygen.

Due to this, the bacteria must be located in environments where there is a high availability of this chemical element..


The bacterium is mainly found in a telluric habitat, that is, on land. It is also found in water, dust, and decaying vegetation..

This bacterium is not part of the normal microbiota of any living being, be it human or animal.

Not demanding

The Nocardia asteroides it does not require many demands to be able to develop. It can grow in a pH range between 6.9 and 9.0.

Likewise, the optimum growth temperature is 35-37 ° C. Despite this, cases have been seen where it has grown at temperatures as low as 12 ° C or as high as 48 ° C.

It is catalase positive

This bacterium synthesizes the enzyme catalase, whose function is to catalyze the conversion of hydrogen peroxide (HtwoORtwo) in water and oxygen, with the consequent appearance of bubbles.

It is slow growing

When culturing this bacterium, it can take 48 hours to 4 weeks for colonies to appear..

It is urease positive

Nocardia asteroides synthesizes the enzyme urease. This enzyme catalyzes the reaction through which the hydrolysis of urea occurs. The reaction is as follows:

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


The Nocardia asteroides it is a widely known human pathogen. In fact, it is the species of the genus Nocardia that most commonly causes human infections.

This bacterium is associated with several pathologies, such as pulmonary nocardiosis, primary cutaneous nocardiosis, keratitis and endophthalmitis.

Pulmonary nocardiosis

This is a disease of the lung tissue caused by the infection and uncontrolled proliferation of Nocardia asteroides there.

It occurs mainly when the bacteria is inhaled.


The symptoms that occur in this infection are similar to those of pneumonia. Among these are:

  • Persistent cough with purulent expectoration
  • Difficulty breathing
  • High fever
  • General discomfort
  • Profuse night sweats
  • Chest pain.

Primary cutaneous nocardiosis

It is an uncommon and extremely rare infection. It attacks people who have a suppressed immune system, such as those who are HIV positive or who have had an organ transplant, among others.


  • Nodular-looking skin lesion that may present with a central pustule
  • Local pain
  • Abscess with purulent discharge
  • Fever
  • General discomfort


It is an infection that is limited to one of the outermost layers of the eye, the cornea. When not treated properly, it can cause complete loss of vision in the affected eye..


  • Eye pain
  • Eye redness
  • Decreased vision
  • Excess tearing or other eye secretions
  • Sensitivity to light
  • Sensation of a foreign body in the eye


It is an infection that affects all parts of the eye. It is caused by the penetration of the bacteria in the eye through an injury, by surgery or directly by the bloodstream.


  • Severe pain in the affected eye
  • Redness of the sclera (white part of the eye)
  • Extreme sensitivity to light
  • Edema around the eyes


As in any bacterial infection, the treatment to follow is with antibiotics. When making the diagnosis, the doctor is obliged to make a culture of the bacteria and determine which antibiotic the infecting strain is susceptible to..

Medications used to treat the above conditions include cotrimoxasol, sulfadiazine, sulfamethoxasol, minocycline, and trimetropin..

Likewise, sometimes, apart from drug treatment, surgical treatment is required, such as to drain purulent collections..


  1. Azuma, I., Kanetsuna, F., Tanaka, Y., Mera, M., Yanagihara, Y., Mifuchi, I. and Yamamura, Y. (1973). Partial Chemical Characterization of the Cell Wall of Nocardia asteroides Strain 131. Japanese Journal of Microbiology Banner. 17 (2). 154-159
  2. Retrieved from:
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  8. Voiland, M. (1985). Structural studies of the cell wall polysaccharide of Nocardia asteroids. Retrieved from:

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