Mycobacterium simiae is a microorganism that belongs to the broader category of nontuberculous mycobacteria (NTM). These bacteria are distinct from Mycobacterium tuberculosis, which causes tuberculosis. While less commonly discussed than some other microorganisms, M. simiae is a recognized bacterium that can impact human health.
Understanding Mycobacterium Simiae
Mycobacterium simiae is a species of bacterium within the Mycobacterium genus. It is a nontuberculous mycobacterium (NTM). This bacterium is known for being slow-growing, which can complicate its identification in laboratory settings. It is also classified as a photochromogen, indicating it produces pigment only when exposed to light.
The bacterium was first identified in monkeys in 1965, which is where it derives its name, “simiae,” meaning “of monkeys”. While it shares some characteristics with Mycobacterium tuberculosis, such as being acid-fast, it behaves differently and requires distinct diagnostic and treatment approaches.
Where Mycobacterium Simiae is Found
Mycobacterium simiae is an environmental organism, found in various natural and municipal settings. It often resides in water sources, including tap water, shower water, and natural bodies of water. Soil is another common habitat for this bacterium.
Humans can be exposed to M. simiae through contact with these environmental reservoirs, for example, by inhaling aerosols from contaminated water. While exposure is possible through these routes, person-to-person transmission of M. simiae is considered rare. Geographically, clusters of M. simiae have been identified in regions such as Arizona, Cuba, and Israel.
Health Conditions Caused by Mycobacterium Simiae
Mycobacterium simiae can lead to various health conditions, primarily affecting the lungs. Pulmonary disease caused by M. simiae can present with symptoms such as chronic cough, sputum production, weight loss, fever, night sweats, and chest pain. Radiological findings in pulmonary infections often include micronodular or “tree-in-bud” lesions and bronchiectasis.
While it can cause serious illness, M. simiae is not as common a cause of NTM infection as some other species. Infections are more frequently observed in individuals with pre-existing lung conditions, such as bronchiectasis or chronic obstructive pulmonary disease, or those with weakened immune systems. Disseminated infections, where the bacteria spread beyond the lungs, can also occur, particularly in immunocompromised individuals, mimicking symptoms of other mycobacterial infections.
Diagnosis and Treatment Approaches
Diagnosing Mycobacterium simiae infections typically involves specialized laboratory procedures. Samples, such as sputum or bronchoalveolar lavage fluid, are collected and cultured to grow the bacteria. Due to its slow-growing nature, identification can be challenging, and molecular tests are often used to confirm the species. Differentiating M. simiae from Mycobacterium tuberculosis is important, as their treatment regimens differ, and M. simiae is the only niacin-positive NTM.
Treatment for M. simiae infections is complex and often requires a prolonged course of multiple antibiotics. Treatment often involves macrolide-based regimens, including clarithromycin or azithromycin, combined with other drugs like ethambutol, rifampicin, moxifloxacin, or amikacin. Treatment can extend for 12 to 18 months. Treatment outcomes can vary, and susceptibility testing of the isolated strain is often performed to guide antibiotic selection, as M. simiae strains can exhibit low susceptibility to some antibiotics.