Nontuberculous mycobacteria, also known as environmental mycobacteria, atypical
mycobacteria and mycobacteria other than tuberculosis, are mycobacteria which do
not cause tuberculosis or Hansen's disease.
Introduction Mycobacteria are a family of small,
rod-shaped bacilli that can be classified into 3 main groups for the
purpose of diagnosis and treatment: Mycobacterium tuberculosis complex which
can cause tuberculosis: M. tuberculosis, M. bovis, M. africanum, M. microti and
M. canetti. M. leprae and M. lepromatosis' which
cause Hansen's disease or leprosy. Nontuberculous mycobacteria are all the
other mycobacteria which can cause pulmonary disease resembling
tuberculosis, lymphadenitis, skin disease, or disseminated disease.
Taxonomy In 1959, botanist Ernest Runyon put
these human disease-associated bacteria into four groups:
Photochromogens, which develop pigments in or after being exposed to light.
Examples include M. kansasii, M. simiae and M. marinum.
Scotochromogens, which become pigmented in darkness. Examples include M.
scrofulaceum and M. szulgai. Non-chromogens, which includes a group
of prevalent opportunistic pathogens called M. avium complex. Other examples
are M. ulcerans, M. xenopi, M. malmoense, M. terrae, M. haemophilum and
M. genavense. Rapid growers include four well
recognized pathogenic rapidly growing non-chromogenic species: M. chelonae, M.
abscessus, M. fortuitum and M. peregrinum. Other examples cause disease
rarely, such as M. smegmatis and M. flavescens.
The number of identified and cataloged NTM species has been increasing rapidly,
from about 50 in 1997 to over 125 by January 2007. The surge is mainly due to
improved isolation and identification technique.
However, even with these new techniques, the Runyon classification is still
sometimes used to organize the mycobacteria into categories.
Epidemiology NTM are widely distributed in the
environment, particularly in wet soil, marshland, streams, rivers and
estuaries. Different species of NTM prefer different types of environment.
Human disease is believed to be acquired from environmental exposures, and unlike
tuberculosis and leprosy, there has been no evidence of animal-to-human or
human-to-human transmission of NTM, hence the alternative label
"environmental bacteria". NTM diseases have been seen in most
industrialized countries, where incidence rates vary from 1.0 to 1.8
cases per 100,000 persons. Recent studies, including one done in Ontario,
Canada, suggest that incidence is much higher. Pulmonary NTM is estimated by
some experts in the field to be at least ten times more common than TB in the
U.S., with at least 150,000 cases per year.
Most NTM disease cases involve the species MAC, M. abscessus, M. fortuitum
and M. kansasii. M. abscessus is being seen with increasing frequency and is
particularly difficult to treat. Mayo Clinic researchers found a
three-fold increased incidence of cutaneous NTM infection between 1980 to
2009 in a population-based study of residents of Olmsted County, Minnesota.
The most common species were M. marinum, accounting for 45% of cases and M.
chelonae and M. abscessus, together accounting for 32% of patients. M.
chelonae infection outbreaks, as a consequence of tattooing with infected
ink, have been reported in the United Kingdom and the United States.
Rapidly growing NTMs are implicated in catheter infections, post-LASIK, skin
and soft tissue and pulmonary infections.
Pathogenesis The most common clinical manifestation
of NTM disease is lung disease, but lymphatic, skin/soft tissue, and
disseminated disease are also important. Pulmonary disease caused by NTM is most
often seen in post-menopausal women. It is not uncommon for cystic fibrosis,
Alpha-1 Antitrypsin Deficiency, Marfan Syndrome and Primary ciliary dyskinesia
patients to have pulmonary NTM colonization and/or infection. Pulmonary
NTM can also be found in individuals with AIDS and malignant disease. It can
be caused by many NTM species which depends on region, but most frequently
MAC and M. kansasii. Lymphadenitis can be caused by various
species that is different from one place to another; but again, MAC is the main
cause worldwide. Most patient are aged less than 5 years, but the incidence is
rare for children having BCG vaccine. The disease has a high curability.
Soft tissue disease due to NTM infection include post-traumatic abscesses,
swimming pool granuloma and Buruli ulcer. Post-traumatic abscesses most
commonly occur after injection. Disseminated mycobacterial disease was
common in US and European AIDS patients in the 1980s and early 1990s, though the
incidence has declined in developed nations since the introduction of highly
active antiretroviral therapy. It can also occur in individuals after having
renal transplantation. Diagnosis
Diagnosis of opportunistic mycobacteria is made by repeated isolation and
identification of the pathogen with compatible clinical and radiological
features. Similar to M. tuberculosis, most nontuberculous mycobacteria can be
detected microscopically and grow on Löwenstein-Jensen medium. Many reference
centres now use a nucleic acid-based method such as sequence differences
detection in the gene coding for 16S ribosomal RNA to identify the species.
Pulmonary NTM disease diagnosis requires both identification of the mycobacterium
in the patient's lung(s) as well as a high resolution CT scan of the lungs.
Research Virginia Tech conducted a home water
supply and patient sputum comparison study to determine source of infection
in pulmonary NTM cases. This study was funded by NTM Info & Research and
results were made by mid-2009, and the study can be found at the CDC:
Nontuberculous Mycobacteria from Household Plumbing of Patients with
Nontuberculous Mycobacteria Disease An epidemiology study on pulmonary NTM
was conducted by National Institute of Allergy & Infectious Disease and results
published in 2010. This study was funded by NTM Info & Research. The data can be
found at PubMed here: "Nontuberculous Mycobacterial Lung Disease Prevalence at
Four Integrated Health Care Delivery Systems"
French researchers finalized the genome sequence of M. abscessus in March 2008.
The genome is available at rez?db=genome&cmd=search&term=abscessus.
Colorado State University have a massive research department dedicated soley to
Mycobacteria research. It is dubbed the MRL, which stands for the Mycobacteria
Research Lab. The MRL, among many Mycobacteria species, studies the
pathogenesis and drug resistance of NTMs. Specifically, Dr. Mary Ann
DeGroote, a researcher at Colorado State University is conducting research on
novel therapies for nontuberuclous mycobacterial infections.
Notes References
Griffith, David E.; Aksamit, Timothy; & A. Brown-Elliott, Barbara et al..
American Thoracic Society Guidelines: Diagnosis, Treatment and Prevention of
Nontuberculous Mycobacterial Diseases. Am. J. Respiratory and Critical Care
Medicine, Vol. 175, pp. 367–417. Grange, J. M.. "Environmental
mycobacteria". In Greenwood, David; Slack, Richard; Peitherer, John; &
Barer, Mike, Medical Microbiology, pp. 221–227. Elsevier. ISBN
978-0-443-10209-7. External links
The NTM Handbook: A Guide for Patients with Nontuberculous Mycobacterial
Infections Including MAC NTM Info & Research, a nonprofit
research and patient support organization
Stop NTM Now National Jewish Medical and Research
Center University of Texas, Tyler Health Center
Lung, Nontuberculous Mycobacterial Infections from eMedicine Radiology