From Medscape Infectious Diseases > Expert Reviews and Commentary
Mycobacteria: September 2006
Published: 09/12/2006
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The authors provide an "invited article" on rapidly growing mycobacteria.
Definition: The simple definition is that these mycobacteria "form mature colonies on solid agar in 7 days (from subculture)." The main clinically important members are Mycobacterium fortuitum, M chelonae, and M abscessus.
Source: These organisms are ubiquitous in nature and found in a wide range of sources including water, soil, rocks, and bioaerosols. They survive harsh environments, and biofilm formation is one of the strategies to do it.
Infection vs Pseudoinfection: Pseudoinfections are common due to contaminated instruments, contaminated solutions, and laboratory cross-contamination. A pseudo-outbreak should be suspected when there is a cluster from laboratory reporting without true evidence of infection or an atypical host.
Infections: Table 1 summarizes 5 categories of infection: (1) catheter infections, (2) keratomileusis, (3) soft tissue, (4) pulmonary, and (5) disseminated disease.
Treatment: Table 2 summarizes the drugs used for the major 3 pathogens in this group. Skin and soft tissue infections are usually treated for 3-6 months with excellent probability of cure, sometimes with assistance of surgical debridement. Pulmonary disease involving M abscessus is generally treated with intermittent intravenous imipenem or cefoxitin plus a macrolide; this infection is rarely "cured." Pulmonary infection due to M fortuitum, by contrast, is often successfully treated with 2-3 antibiotics given for 12-24 months. A common regimen is sulfamethoxazole, moxifloxacin, and minocycline. Drugs selected for skin and soft tissue infections are usually intravenous imipenem or cefoxitin combined with amikacin.
Table 1. Types of Infections Due to Rapidly Growing Mycobacteria
| Infection | Comment |
|---|---|
| Catheters And Devices | |
| Intravenous lines | Risks -- immunosuppression, catheter duration, prior antibiotics. Remove catheter . |
| Pocket infections, pacemaker, etc. | Usually Mycobacterium abscessus. Remove device . |
| Dialysis-peritonitis | Usually from contaminated solution to sterilize reusable filters. |
|
Laser In Situ Keratomileusis
(LASIK) surgery |
Complication of laser surgery. Presents with crystalline opacities in corneal stroma. |
| Soft Tissue | |
| Post injection | Adrenal cortex injections -- naturopathic treatments |
| Furunculosis | Whirlpool footbaths |
| Pulmonary Infection | Multiple risks defined,* but many infected hosts do not have these. May cause hypersensitivity pneumonitis requiring removal of patient source. |
| Disseminated Disease | Occurs in immunocompromised patients: organ transplant, HIV, or patients with defects in cytokine pathways. |
*Defined risks include: (1) lung diseases: chronic bronchitis, bronchiectasis, pulmonary fibrosis, radiation lung injury, lung cancer; (2) inherited conditions: alpha-1 antitrypsin deficiency, cystic fibrosis, cilia motility disorder; (3) slender body habitus: women with pectus excavatum or scoliosis; (4) prior lung infections or granulomatous disease: histoplasmosis, coccidioidomycosis, sarcoidosis; (5) aspiration; (6) hypersensitivity pneumonitis; and (7) endocrine or immune disorders: panhypopituitarism, Cushing disease, or gamma-interferon or interleukin-12 deficiency.
Table 2. Antimicrobials Used to Treat the 3 Major Pathogens of Rapidly Growing Mycobacteria
| Agent | Regimen | Mycobacterium abscessus | Mycobacterium chelonae | Mycobacterium fortuitum |
|---|---|---|---|---|
| Clarithromycin | 500 mg bid po | + | + | + |
| Azithromycin | 250-500 mg qd po | + | + | + |
| Doxycycline | 100 mg bid po | + | + | + |
| Minocycline | 100 mg bid po | + | + | + |
| Ciprofloxacin | 500-750 mg bid po | + | + | + |
| Cefoxitin | 1-2 gm q 6-8 h IV | + | -- | -- |
| Imipenem | 1 gm q 12 h IV | + | + | -- |
| Amikacin | 12-15 mg/kg 3x/wk IV | + | -- | -- |
| Tobramycin | 2.5 mg/kg q 12 h IV | -- | + | -- |
| Linezolid | 600 mg/d IV/po | -- | + | -- |
| Tigecycline | 50 mg bid IV | -- | + | -- |
3x/wk = 3 times per week; bid = twice daily; h = hours; IV = intravenous; po = by mouth; q 6-8 h = every 6-8 hours; q 12 h = every 12 hours; qd = once daily.
Authors and Disclosures
John G. Bartlett, MD, Professor of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland
Disclosure: John G. Bartlett, MD, has disclosed that he has served on the HIV advisory board for Bristol-Myers Squibb, Abbott, and GlaxoSmithKline.
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Authors and Disclosures
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Medscape Infectious Diseases. 2006;8(2) © 2006 Medscape