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Study identifies nontuberculous mycobacteria strains linked to corneal infection
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Two strains of nontuberculous mycobacteria, Mycobacterium chelonae and Mycobacterium abscessus, were the species most frequently associated with ophthalmic infection over a period of 27 years, a study found.
“This study emphasizes that [nontuberculous mycobacteria] need to be kept in mind as part of the differential diagnosis of ophthalmic infections, especially atypical or poorly responsive infections,” the study authors said. “This large series further documents antibiotic susceptibilities that should be considered in the setting of increasing fluoroquinolone resistance.”
Investigators examined 112 clinical nontuberculous mycobacteria eye isolates from 100 patients submitted to a single nontuberculous mycobacteria reference laboratory between 1982 and 2009.
Polymerase chain reaction and restriction fragment length polymorphism of the hsp65 gene were used to identify isolates, which were tested against 10 antimicrobial agents such as besifloxacin.
Study results showed that M. abscessus was the most commonly isolated pathogen in the 1980s, and M. chelonae was most commonly isolated in the 1990s. M. chelonae was responsible for more than 50% of all cases of infection by 2000.
M. abscessus and Mycobacterium fortuitum most commonly originated in the southern coastal states and Texas; M. chelonae isolates were more geographically widespread.
Amikacin and clarithromycin/azithromycin were the most active antimicrobials for M. abscessus. Clarithromycin/azithromycin, amikacin, tobramycin and the quinolones were most active for M. chelonae.
Perspective
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Marguerite B. McDonald, MD
This is the largest study of nontuberculous mycobacteria (NTM) or atypical mycobacteria ophthalmic isolates that has ever been performed. It is also the first study to include susceptibilities and molecular identification methods for all isolates studied. The size of this study is also impressive and important: 112 isolates from 100 patients. The results suggest that combinations of potent topical fluoroquinolones with clarithromycin are recommended for managing the risks associated with ocular infections caused by these NTM.
In their discussion, the authors suggest that newer quinolones are preferred because of reports of the development of resistance with systemically administered quinolones.
Most importantly, this study reminds us to keep NTM on the list when contemplating the differential diagnosis of ophthalmic infections, especially unusual or poorly responsive infections.
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Cornea. 2012;31(8):900-906.
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