Mycobacterium chelonae: Overview and Treatment
What is Mycobacterium chelonae?
M. chelonae is a rapidly growing nontuberculous mycobacterium that primarily causes skin, bone, and soft tissue infections, with treatment being substantially easier than its close relative M. abscessus. 1
Key Organism Characteristics
- Ubiquitous environmental organism found in water and soil that enters through direct inoculation via trauma, surgery, or contaminated medical procedures 1, 2
- Rapid growth distinguishes it from slow-growing mycobacteria, allowing culture identification within days rather than weeks 1
- Critical to differentiate from M. abscessus since therapy for M. chelonae is potentially easier 1
Clinical Presentations
Primary Manifestations (Most Common)
Skin, bone, and soft tissue disease are the most important clinical manifestations 1:
- Localized infections at puncture wound sites, surgical sites, or traumatic injuries 1
- Nosocomial infections including post-injection abscesses, infections after liposuction, augmentation mammaplasty, cardiac bypass surgery 1, 3
- Chronic granulomatous infections of tendon sheaths, bursae, joints, and bones after direct inoculation 1
- Catheter-related infections involving long-term intravenous or peritoneal catheters 1
Ocular Disease
- M. chelonae is the most frequently reported etiologic agent in LASIK-associated keratitis 1
- Associated with contact lens wear and ocular surgery 1
- Outcome for vision is typically poor, often requiring corneal transplant 1
Disseminated Disease
- Occurs primarily in immunocompromised patients, particularly those with advanced HIV (very low CD4 counts), organ transplantation (especially renal), or hematologic malignancies 4, 5
- Presents with characteristic skin lesions 1
- Extremely rare in immunocompetent individuals, where infections tend to remain localized 4, 2
Pulmonary Disease
- Less common cause of pulmonary disease than M. abscessus 1
- Symptoms and radiographic presentation similar to M. abscessus and M. fortuitum 1
Antimicrobial Susceptibility Profile
M. chelonae demonstrates predictable susceptibility patterns that guide treatment selection 1:
- Tobramycin: 100% susceptibility (more active than amikacin for M. chelonae) 1
- Clarithromycin: 100% susceptibility 1
- Linezolid: 90% susceptibility 1
- Imipenem: 60% susceptibility (preferred over cefoxitin, to which M. chelonae is uniformly resistant) 1
- Amikacin: 50% susceptibility 1
- Doxycycline: 25% susceptibility 1, 6
- Ciprofloxacin: 20% susceptibility 1
- Additional agents: clofazimine 1
Treatment Recommendations
Skin and Soft Tissue Infections
Mild, Localized Disease
For uncomplicated skin disease, clarithromycin monotherapy at 500 mg twice daily for 6 months achieved cure in 92% of patients in the only clinical treatment trial 1. However, one patient (8%) relapsed with mutational resistance to clarithromycin 1.
Serious Skin, Bone, and Soft Tissue Disease
A minimum of 4 months of combination drug therapy is necessary to provide high likelihood of cure and minimize macrolide resistance risk 1, 6:
- Initial combination therapy with clarithromycin plus a second agent based on susceptibility (tobramycin or imipenem preferred) 1, 6
- For bone infections: 6 months of therapy is recommended 1
- Surgery is generally indicated with extensive disease, abscess formation, or where drug therapy is difficult 1, 6
- Removal of foreign bodies (breast implants, catheters) is important or essential to recovery 1
Treatment Failure or Persistent Infection
Complete surgical excision of affected tissue combined with optimized antimicrobial therapy is the treatment of choice 6:
- Obtain new cultures during excision for updated susceptibility testing 6
- Consider parenteral agents like tobramycin (100% susceptibility) or imipenem (60% susceptibility) 6
- Continue combination therapy for at least 4-6 months post-excision 6
- If surgery contraindicated, use aggressive parenteral therapy with tobramycin plus imipenem for at least 12 months of negative cultures 6
Corneal Infections
First-line treatment involves topical and oral agents 1:
- Amikacin, fluoroquinolones, clarithromycin, and azithromycin are usual drugs of choice depending on susceptibility 1
- Many patients require corneal transplant for vision recovery or infection cure 1
Pulmonary Disease
Optimal therapy for M. chelonae lung disease is unknown 1:
- Based on in vitro susceptibilities, a regimen including clarithromycin with a second agent (based on susceptibilities) would likely be successful 1
- Treatment duration should follow principles established for other nontuberculous mycobacterial lung infections 1
Disseminated Disease in Immunocompromised Patients
Effective treatment involves combination antibiotics with clarithromycin and azithromycin as long-term therapy, plus linezolid and tigecycline for acute dissemination management 5:
- Clarithromycin and azithromycin form the backbone of long-term treatment 5
- Linezolid and tigecycline added for managing acute disseminated disease 5
- Prolonged multi-drug therapy essential for successful outcomes 2
Critical Clinical Pitfalls
Diagnostic Challenges
- Prolonged skin lesions resistant to standard antibiotics should raise suspicion for M. chelonae in both immunocompromised and immunocompetent patients 7
- Tissue biopsy is the most sensitive means of obtaining specimens for culture; fine needle aspiration or incision/drainage may lead to fistula formation with chronic drainage 1
- Only 50-82% of excised nodes yield positive cultures even with compatible histopathology 1
- Nonspecific symptoms (pain, erythema, draining subcutaneous nodules) make diagnosis difficult without prior suspicion 3
Treatment Considerations
- Monotherapy risks macrolide resistance development; combination therapy should be used initially for serious infections 1, 6
- Inadequate drug penetration into lymph nodes may contribute to treatment failure 6
- Long-term follow-up is essential to ensure complete eradication 4
- Doxycycline has only 25% susceptibility and may explain treatment failures when used 6