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Tathagata Mukherjee, Helena Boshoff, Clifton E. Barry, Comment on: Identification of antimicrobial activity among FDA-approved drugs for combating Mycobacterium abscessus and Mycobacterium chelonae, Journal of Antimicrobial Chemotherapy, Volume 67, Issue 1, January 2012, Pages 252–253, https://doi.org/10.1093/jac/dkr418
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Sir,
In the article titled ‘Identification of antimicrobial activity among FDA-approved drugs for combating Mycobacterium abscessus and Mycobacterium chelonae’ published in the July 2011 issue of JAC, it was reported that the FDA-approved drug metronidazole has potent activity (<0.015 mg/L; ∼87 nM) against the rapid-growing mycobacteria (RGM) Mycobacterium abscessus.1 This finding intrigued us and our clinical colleagues who treat M. abscessus-infected patients here at NIH. We therefore tried to repeat their experiment with M. abscessus ATCC 19977 and some recent patient isolates of M. abscessus to evaluate their susceptibility to metronidazole. We regret to report that we did not observe any MIC99, even at the highest concentration of the drug we tested (2 mM) after 48, 72 and 96 h.
In accordance with the method published in the paper, we grew the M. abscessus ATCC 19977 (and four clinical isolates) from glycerol stock in 7H9 Middlebrook medium, passaged them once and let them grow to an OD650 of 0.2–0.4. The cell cultures were then diluted to an OD650 of 0.0002 in 7H9 medium and 50 μL of the cells was added to 50 μL of drug at various concentrations in a 96-well plate. They were incubated at 37°C for 48, 72 and 96 h and no killing of this RGM was observed (Figure 1a).
