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      We appreciate the important observations made by Su et al
      • Su S-.Y.
      • Chao C.-M.
      • Lai C.-C.
      Other than “Rhodococcus”.
      regarding the tuberculosis-like pneumonias caused by bacterial organisms of the Actinomycetales order. The Actinomycetales group includes phylogenetically diverse but morphologically similar aerobic and anaerobic actinomycetes such as Actinomyces, Rothia, Williamsia, Gordonia, Tsukamurella, and Rhodococcus.
      • Savini V.
      • Fazii P.
      • Favaro M.
      • et al.
      Tuberculosis-like pneumonias by the aerobic actinomycetes Rhodococcus, Tsukamurella, and Gordonia.
      As a group, these organisms exhibit filamentous branching structures, which may fragment into rods, or coccoid forms. This morphological variability is one of the reasons why acid-fast bacilli organisms such as Mycobacterium, Tsukamurella, and Rhodococcus (aerobic actinomycetes) may be confusing even for experienced microbiologists. The differentiation of these 3 genera, as well as their species identification, is difficult, and often responsible for delayed or inappropriate diagnosis. Therefore, we concur with Su et al
      • Su S-.Y.
      • Chao C.-M.
      • Lai C.-C.
      Other than “Rhodococcus”.
      that phenotypic similarity in culture media of these pathogens may lead to species misidentification and thus, molecular identification should be routinely performed. In our report,
      • Franco-Paredes C.
      • Ray S.
      Causes of persistent acid-fast positive smears in pulmonary tuberculosis.
      Rhodococcus was identified by standard microbiological methods (high-performance liquid chromatography) and by molecular characterization at the reference public health laboratory. In summary, the aerobic actinomycetes such as Gordonia, Rhodococcus, and Tsukamurella are increasingly recognized clinical pathogens that cause tuberculosis-like pneumonias. We agree with Su et al
      • Su S-.Y.
      • Chao C.-M.
      • Lai C.-C.
      Other than “Rhodococcus”.
      about the importance of identifying actinomycetes to the molecular level for epidemiological reasons and to provide optimal clinical therapies.

      References

        • Su S-.Y.
        • Chao C.-M.
        • Lai C.-C.
        Other than “Rhodococcus”.
        Am J Med. 2013; 126: e15
        • Savini V.
        • Fazii P.
        • Favaro M.
        • et al.
        Tuberculosis-like pneumonias by the aerobic actinomycetes Rhodococcus, Tsukamurella, and Gordonia.
        Microb Infect. 2012; 14: 401-410
        • Franco-Paredes C.
        • Ray S.
        Causes of persistent acid-fast positive smears in pulmonary tuberculosis.
        Am J Med. 2012; 125: e3-e4

      Linked Article

      • Other than “Rhodococcus”
        The American Journal of MedicineVol. 126Issue 7
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          Franco-Paredes and Ray report a case of persistent acid-fast positive smear due to Rhodococcus equi.1 The reported case reminds us of the possibility of non-Mycobacterium species microorganism with positive acid-fast stain. However, we are concerned about 2 important issues that need to be clarified.
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