Nocardia Spp. Bacteria: Infections, Causes, and Treatment

Nocardia spp. is a genus of bacteria found throughout the world in various environments. These microbes are part of a group called aerobic actinomycetes and are gram-positive. One of their most distinct features is their appearance under a microscope, where they grow in long, branching, thread-like filaments that can be mistaken for fungi. This unique, filamentous structure is a defining characteristic of the genus. The bacteria are also described as partially acid-fast, a staining property they share with related bacteria due to the presence of mycolic acids in their cell walls.

Environmental Sources and Transmission

Nocardia species are ubiquitous, thriving as saprophytes that feed on dead or decaying organic material. They are commonly found in soil, dust, decomposing vegetation, and aquatic environments. The primary ways people become infected are through inhalation or direct contact with contaminated sources.

Inhaling dust or soil particles containing Nocardia can lead to infection in the lungs, which is the most common route of transmission. Alternatively, the bacteria can enter the body through a cut or scrape that comes into contact with contaminated soil or water, though person-to-person spread is rare.

Types of Nocardial Infections

The disease caused by Nocardia bacteria is called nocardiosis, and it can manifest in several forms depending on the site of infection. The most frequent presentation is pulmonary nocardiosis, which develops after the bacteria are inhaled into the lungs. Symptoms are often nonspecific and can resemble other respiratory illnesses like tuberculosis or pneumonia. Patients may experience a persistent cough, fever, chills, chest pain, weakness, and unintended weight loss.

When the bacteria enter through a break in the skin, it results in cutaneous nocardiosis. This form of infection may present as a localized skin abscess, cellulitis, or as nodules or ulcerations. Nocardia brasiliensis is a species frequently associated with these skin infections, particularly in warmer climates.

In some cases, the infection can spread from its original location to other parts of the body, a condition known as disseminated nocardiosis. This occurs when the bacteria travel through the bloodstream to infect other organs. It most commonly targets the brain, skin, kidneys, or bones. Brain involvement is particularly dangerous, as the infection can lead to the formation of brain abscesses, causing severe headaches and specific neurological problems.

Populations at Increased Risk

Nocardiosis is an opportunistic infection, meaning it most often affects individuals with weakened immune systems. While healthy people can become infected, the risk of developing severe pulmonary or disseminated disease is much higher in those with compromised immunity. A large portion of patients diagnosed with nocardiosis have an underlying condition that impairs their body’s ability to fight infections.

Several specific groups are at a heightened risk. Organ transplant recipients are particularly vulnerable due to the immunosuppressive drugs they must take. Similarly, patients receiving long-term corticosteroid therapy or other immunosuppressants face an increased risk. Other at-risk populations include individuals with advanced HIV infection, patients with cancer undergoing chemotherapy, and individuals with chronic lung diseases, such as COPD.

Diagnosis and Treatment Protocols

Diagnosing nocardiosis can be a complex process because its symptoms overlap with many other infections and the bacteria grow slowly in laboratory settings. A diagnosis begins with collecting a sample from the suspected site of infection, such as sputum, pus, or a tissue biopsy. These samples are then examined under a microscope and cultured to grow the bacteria for identification.

Technicians use specific staining methods, like the Gram stain and a modified acid-fast stain, to look for the characteristic beaded, branching filaments of Nocardia. Imaging studies are also frequently used to locate infections. Chest X-rays and computed tomography (CT) scans can reveal signs of pulmonary infection or help identify abscesses in the brain or other organs.

Treatment for nocardiosis requires long-term antibiotic therapy, often lasting for six months to a year to ensure the infection is fully eradicated. The choice of antibiotic depends on the species of Nocardia and its susceptibility, but sulfonamides are the primary drugs for treatment. In certain situations, large abscesses may need to be surgically drained in conjunction with the antibiotic regimen to effectively manage the infection.