Mycobacteria: September 2006

John G. Bartlett, MD


September 12, 2006

De Groote MA, Huitt G. Infections due to rapidly growing mycobacteria. Clin Infect Dis. 2006;42:1756-1763.

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.


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