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The mycobacteriology of non-tuberculous mycobacteria
PAEDIATRIC RESPIRATORY REVIEWS (2004) 5(Suppl A), S221–S223
The mycobacteriology of non-tuberculous mycobacteria Lisa Saiman° Columbia University, New York, NY, USA
Summary The genus Mycobacterium consists of >50 species that have been associated with human disease. Mycobacterium are categorised into M. tuberculosis and NTM that are also subdivided into rapid growers and non-rapid growers. Five major clinical syndromes have been described that are attributable to mycobacterium. These include: pulmonary disease; lymphadenitis; skin, soft tissue, and skeletal infections; catheter-related blood-stream infections in immunocompromised hosts; and disseminated disease in persons with AIDS. There is very limited documentation of person-to-person transmission of NTM. Nosocomial infections and outbreaks caused by inadequate disinfection/sterilisation of medical devices or environmental contamination of medications or medical devices are well described. Staining for AFB, culture, histopathologic, or genetic amplification technologies are used to detect and identify mycobacterium. Pulsedfield gel electrophoresis is the method of choice to determine strain relatedness. At present, susceptibility testing for non-tuberculous mycobacteria is not fully standardised and has not been correlated with clinical outcomes. © 2004 Elsevier Science Ltd.
INTRODUCTION With the increase in TB and the advent of HIV/AIDS, there has been a resurgence in interest in mycobacteria and increase in diseases caused by non-tuberculous mycobacteria (NTM). It is increasingly recognised that CF patients may be infected or colonised with NTM. Other classifications for NTM have included: “atypical mycobacteria” or “mycobacteria other than M. tuberculosis” (MOTT).
TAXONOMY The genus Mycobacterium consists of >50 species that have been associated with human disease.1−6 Mycobacterium are categorised into M. tuberculosis and NTM. NTM are further subdivided into rapid growers and non-rapid growers. Rapid growers require <7 days to produce a visible colony in culture media, while non-rapid growers can require * Correspondence to: Lisa Saiman. E-mail: [email protected] Correspondence address: Columbia University, 650 West 168th St., New York, NY 10032, USA (No reprints)
1526-0542/$ – see front matter
up to 8 weeks of incubation. The cell walls of mycobacterium have a high lipid content with characteristic mycolic acids with long branched chains. Mycobacteria resist decolorisation by acidalcohol, hence the term acid-fast bacteria (AFB).
MAJOR CLINICAL SYNDROMES Five major clinical syndromes have been described that are attributable to mycobacteria (see Table 1). These include: pulmonary disease; lymphadenitis; skin, soft tissue, and skeletal infections; catheterrelated blood-stream infections in immunocompromised hosts; and disseminated disease in persons with AIDS.
ECOLOGIC NICHE Most species are free-living and ubiquitous in the environment and have been found in soil, plants, house dust, and water. M. tuberculosis and M. leprae live in humans, and person-to-person transmission is the mode of acquisition. In general, animals © 2004 Elsevier Science Ltd. All rights reserved.
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Table 1 Common Mycobacterium, characteristics, and their association with human disease Species a
Characteristics
Association with human disease
M. tuberculosis complex M. tuberculosis, M. bovis, M. africanum, M. microti
Tuberculosis and latent infection
M. leprae
Cannot be cultured
Leprosy: anesthetic skin lesions and peripheral neuropathy
M. avium
MAC = M. avium complex = M. avium + M. intracellulare
Chronic bronchopulmonary disease (adults), lymphadenitis (children), skeletal infections – non-AIDS Disseminated disease – AIDS
M. intracellulare
Closely related to M. avium
Chronic bronchopulmonary disease – non-AIDS
M. abscessus
Rapid grower, closely related to M. chelonae, found in tap water
Chronic bronchopulmonary disease, skin and soft tissue infections, skeletal infections, nosocomial infections, catheter-related infections
M. chelonae
Rapid grower
Skin nodules in immunosuppressed patients, catheter infections
M. fortuitum group
Rapid grower
Skeletal, skin and soft tissue infections, nosocomial infections, pseudo-outbreaks
M. haemophilum
No environmental reservoir detected Multiple skin nodules, adenopathy, osteomyelitis
M. marinum
Fresh water fish tanks
Skeletal, skin and soft tissue infections
M. kansasii
Found in tap water
Chronic tuberculosis-like lung disease, skeletal infections, disseminated disease second only to MAC in AIDS patients
a
Other species include: M. simiae, M. szulgai, M. gordonae, M. malmoense, M. ulcerans and M. xenopi, as well as several other agents that are less commonly associated with human disease, e.g., M. smegmatis, M. gastri, and M. terrae.
are not an important reservoir for mycobacteria. There is very limited evidence that NTM is transmitted person-to-person, with the exception of inadequately cleaned and disinfected medical equipment. Nosocomial infections and outbreaks caused by inadequate disinfection/sterilisation of medical devices or environmental contamination of medications or medical devices are well described.7
LABORATORY DIAGNOSIS Staining for AFB, culture, histopathologic, or genetic amplification technologies are used to detect and identify mycobacterium.8 Staining for AFB is done using by Kinyoun, Ziehl–Neelsen, Fuchsin or a fluorochrome stain. Respiratory tract cultures that are AFB-smear positive should undergo genetic amplification tests (e.g., PCR-based assays) to distinguish M. tuberculosis from NTM. This is critical to provide appropriate isolation precautions for hospitalised patients, including CF patients. However, these amplification tests do not distinguish among different species of NTM. The most common culture media are Lowenstein– Jensen and Middlebrook 7H10 or 7H11. Culture techniques for CF sputum must utilise a special decontamination step to avoid overgrowth with P. aeruginosa.9 However, the decontamination step may cause a decrease in viable organisms. Probes (once there is visible growth) for different mycobacteria are useful to distinguish M. tuberculosis from other species, including M. avium, M. intracellulare, M. gordonae, and M. kansasii.
Other biochemical tests or analysis of mycolic acids can distinguish different species, e.g., M. bovis from M. tuberculosis, but are generally performed in a reference laboratory.
MOLECULAR EPIDEMIOLOGY Molecular methods such as Southern blots, PCR, or pulsed-field gel electrophoresis (PFGE) “DNA fingerprinting”10 have been used to compare NTM strains during outbreaks or to determine routes of transmission. Currently, PFGE is the technique most commonly used.
SUSCEPTIBILITY TESTING Susceptibility testing has been standardised for M. tuberculosis, and in vitro susceptibility has been correlated with clinical outcome. Unfortunately, similar progress has not been made for nontuberculous mycobacteria, with the exception of clarithromycin. However, agar disks, broth dilution, and E-tests have all been used to test for antibiotic susceptibility. At present, susceptibility testing is not widely available.
REFERENCES 1. Shinnick TM. Good RC. Mycobacterial taxonomy. Eur J Clin Microbiol Infect Dis 1994; 13(11): 884−901. 2. Gangadharam PR. Microbiology of nontuberculosis mycobacteria. Semin Respir Infect 1996; 11(4): 231−243. 3. Wallace Jr RJ. Recent changes in taxonomy and disease manifestations of the rapidly growing mycobacteria. Eur J Clin Microbiol Infect Dis. 1994; 13(11): 953−960.
MYCOBACTERIOLOGY OF NTM 4. Horsburgh CR. Epidemiology of disease caused by nontuberculous mycobacteria. Semin Respir Infect 1996; 9: 244−251. 5. Falkinham JO. Epidemiology of infection by nontuberculous mycobacteria. Clin Microbiol Rev 1996; 9(2): 177−215. 6. Pozniak A. Bull T. Recently recognized mycobacteria of clinical significance. J Infect 1999; 38(3): 157−161. 7. Wallace RJ, Brown BA, Griffith DE. Nosocomial outbreaks/ pseudo-outbreaks caused by nontuberculous mycobacteria. Annu Rev Microbiol 1998; 52: 453−490.
S223 8. Watterson SA. Drobniewski FA. Modern laboratory diagnosis of mycobacterial infections. J Clin Pathol 2000; 53(10): 727−732. 9. Whittier S, Hopfer RL, Knowles MR, Gilligan PH. Improved recovery of mycobacteria from respiratory secretions of patients with cystic fibrosis. J Clin Microbiol 1993; 31: 861−864. 10. Van Soolingen D. Molecular epidemiology of tuberculosis and other mycobacterial infections: main methodologies and achievements. J Intern Med 2001; 249(1): 1−26.
The mycobacteriology of non-tuberculous mycobacteria Lisa Saiman° Columbia University, New York, NY, USA
Summary The genus Mycobacterium consists of >50 species that have been associated with human disease. Mycobacterium are categorised into M. tuberculosis and NTM that are also subdivided into rapid growers and non-rapid growers. Five major clinical syndromes have been described that are attributable to mycobacterium. These include: pulmonary disease; lymphadenitis; skin, soft tissue, and skeletal infections; catheter-related blood-stream infections in immunocompromised hosts; and disseminated disease in persons with AIDS. There is very limited documentation of person-to-person transmission of NTM. Nosocomial infections and outbreaks caused by inadequate disinfection/sterilisation of medical devices or environmental contamination of medications or medical devices are well described. Staining for AFB, culture, histopathologic, or genetic amplification technologies are used to detect and identify mycobacterium. Pulsedfield gel electrophoresis is the method of choice to determine strain relatedness. At present, susceptibility testing for non-tuberculous mycobacteria is not fully standardised and has not been correlated with clinical outcomes. © 2004 Elsevier Science Ltd.
INTRODUCTION With the increase in TB and the advent of HIV/AIDS, there has been a resurgence in interest in mycobacteria and increase in diseases caused by non-tuberculous mycobacteria (NTM). It is increasingly recognised that CF patients may be infected or colonised with NTM. Other classifications for NTM have included: “atypical mycobacteria” or “mycobacteria other than M. tuberculosis” (MOTT).
TAXONOMY The genus Mycobacterium consists of >50 species that have been associated with human disease.1−6 Mycobacterium are categorised into M. tuberculosis and NTM. NTM are further subdivided into rapid growers and non-rapid growers. Rapid growers require <7 days to produce a visible colony in culture media, while non-rapid growers can require * Correspondence to: Lisa Saiman. E-mail: [email protected] Correspondence address: Columbia University, 650 West 168th St., New York, NY 10032, USA (No reprints)
1526-0542/$ – see front matter
up to 8 weeks of incubation. The cell walls of mycobacterium have a high lipid content with characteristic mycolic acids with long branched chains. Mycobacteria resist decolorisation by acidalcohol, hence the term acid-fast bacteria (AFB).
MAJOR CLINICAL SYNDROMES Five major clinical syndromes have been described that are attributable to mycobacteria (see Table 1). These include: pulmonary disease; lymphadenitis; skin, soft tissue, and skeletal infections; catheterrelated blood-stream infections in immunocompromised hosts; and disseminated disease in persons with AIDS.
ECOLOGIC NICHE Most species are free-living and ubiquitous in the environment and have been found in soil, plants, house dust, and water. M. tuberculosis and M. leprae live in humans, and person-to-person transmission is the mode of acquisition. In general, animals © 2004 Elsevier Science Ltd. All rights reserved.
S222
L. SAIMAN
Table 1 Common Mycobacterium, characteristics, and their association with human disease Species a
Characteristics
Association with human disease
M. tuberculosis complex M. tuberculosis, M. bovis, M. africanum, M. microti
Tuberculosis and latent infection
M. leprae
Cannot be cultured
Leprosy: anesthetic skin lesions and peripheral neuropathy
M. avium
MAC = M. avium complex = M. avium + M. intracellulare
Chronic bronchopulmonary disease (adults), lymphadenitis (children), skeletal infections – non-AIDS Disseminated disease – AIDS
M. intracellulare
Closely related to M. avium
Chronic bronchopulmonary disease – non-AIDS
M. abscessus
Rapid grower, closely related to M. chelonae, found in tap water
Chronic bronchopulmonary disease, skin and soft tissue infections, skeletal infections, nosocomial infections, catheter-related infections
M. chelonae
Rapid grower
Skin nodules in immunosuppressed patients, catheter infections
M. fortuitum group
Rapid grower
Skeletal, skin and soft tissue infections, nosocomial infections, pseudo-outbreaks
M. haemophilum
No environmental reservoir detected Multiple skin nodules, adenopathy, osteomyelitis
M. marinum
Fresh water fish tanks
Skeletal, skin and soft tissue infections
M. kansasii
Found in tap water
Chronic tuberculosis-like lung disease, skeletal infections, disseminated disease second only to MAC in AIDS patients
a
Other species include: M. simiae, M. szulgai, M. gordonae, M. malmoense, M. ulcerans and M. xenopi, as well as several other agents that are less commonly associated with human disease, e.g., M. smegmatis, M. gastri, and M. terrae.
are not an important reservoir for mycobacteria. There is very limited evidence that NTM is transmitted person-to-person, with the exception of inadequately cleaned and disinfected medical equipment. Nosocomial infections and outbreaks caused by inadequate disinfection/sterilisation of medical devices or environmental contamination of medications or medical devices are well described.7
LABORATORY DIAGNOSIS Staining for AFB, culture, histopathologic, or genetic amplification technologies are used to detect and identify mycobacterium.8 Staining for AFB is done using by Kinyoun, Ziehl–Neelsen, Fuchsin or a fluorochrome stain. Respiratory tract cultures that are AFB-smear positive should undergo genetic amplification tests (e.g., PCR-based assays) to distinguish M. tuberculosis from NTM. This is critical to provide appropriate isolation precautions for hospitalised patients, including CF patients. However, these amplification tests do not distinguish among different species of NTM. The most common culture media are Lowenstein– Jensen and Middlebrook 7H10 or 7H11. Culture techniques for CF sputum must utilise a special decontamination step to avoid overgrowth with P. aeruginosa.9 However, the decontamination step may cause a decrease in viable organisms. Probes (once there is visible growth) for different mycobacteria are useful to distinguish M. tuberculosis from other species, including M. avium, M. intracellulare, M. gordonae, and M. kansasii.
Other biochemical tests or analysis of mycolic acids can distinguish different species, e.g., M. bovis from M. tuberculosis, but are generally performed in a reference laboratory.
MOLECULAR EPIDEMIOLOGY Molecular methods such as Southern blots, PCR, or pulsed-field gel electrophoresis (PFGE) “DNA fingerprinting”10 have been used to compare NTM strains during outbreaks or to determine routes of transmission. Currently, PFGE is the technique most commonly used.
SUSCEPTIBILITY TESTING Susceptibility testing has been standardised for M. tuberculosis, and in vitro susceptibility has been correlated with clinical outcome. Unfortunately, similar progress has not been made for nontuberculous mycobacteria, with the exception of clarithromycin. However, agar disks, broth dilution, and E-tests have all been used to test for antibiotic susceptibility. At present, susceptibility testing is not widely available.
REFERENCES 1. Shinnick TM. Good RC. Mycobacterial taxonomy. Eur J Clin Microbiol Infect Dis 1994; 13(11): 884−901. 2. Gangadharam PR. Microbiology of nontuberculosis mycobacteria. Semin Respir Infect 1996; 11(4): 231−243. 3. Wallace Jr RJ. Recent changes in taxonomy and disease manifestations of the rapidly growing mycobacteria. Eur J Clin Microbiol Infect Dis. 1994; 13(11): 953−960.
MYCOBACTERIOLOGY OF NTM 4. Horsburgh CR. Epidemiology of disease caused by nontuberculous mycobacteria. Semin Respir Infect 1996; 9: 244−251. 5. Falkinham JO. Epidemiology of infection by nontuberculous mycobacteria. Clin Microbiol Rev 1996; 9(2): 177−215. 6. Pozniak A. Bull T. Recently recognized mycobacteria of clinical significance. J Infect 1999; 38(3): 157−161. 7. Wallace RJ, Brown BA, Griffith DE. Nosocomial outbreaks/ pseudo-outbreaks caused by nontuberculous mycobacteria. Annu Rev Microbiol 1998; 52: 453−490.
S223 8. Watterson SA. Drobniewski FA. Modern laboratory diagnosis of mycobacterial infections. J Clin Pathol 2000; 53(10): 727−732. 9. Whittier S, Hopfer RL, Knowles MR, Gilligan PH. Improved recovery of mycobacteria from respiratory secretions of patients with cystic fibrosis. J Clin Microbiol 1993; 31: 861−864. 10. Van Soolingen D. Molecular epidemiology of tuberculosis and other mycobacterial infections: main methodologies and achievements. J Intern Med 2001; 249(1): 1−26.