Comment on “A case of Mycobacterium chelonae mediastinitis and acute humoral rejection after heart transplantation”

Dear Editor, Dr Sawa et al recently published their report on “A case of Mycobacterium chelonae mediastinitis and acute humoral rejection after heart transplantation. ” The genus Mycobacterium is subdivided in two distinct groups of Mycobacterium tuberculosis complex (such as Mycobacterium tuberculosis sensu stricto, Mycobacterium bovis, M. bovis Bacille Calmette–Guerin [BCG], Mycobacterium africanum, and Mycobacterium microti) and Mycobacterium leprae, which are strictly pathogen and opportunistic pathogens known as Nontuberculosis Mycobacteria (NTM); NTM species are free‐living in the environmental resources such as water, soil, animals, and decaying vegetables, that were not accepted as human pathogens until 1950s. Nowadays, there is a good amount of evidence for transmission of NTM species through hospital environmental resources and contaminated catheter and medical equipment to patients. This group of bacteria can enter human body via inhalation and cutaneous inclusion and cause various infections, such as pulmonary infection, cutaneous, subcutaneous, bone and joint, brain abscess, eye or disseminated infections. Nontuberculosis mycobacterium species are acid‐fast bacteria and the clinical symptoms, radiological evidence, or isolation method of this bacteria are very similar to Mycobacterium tuberculosis complex (MTBC); thus, NTM infections can be easily misdiagnosed as MTBC infections. Moreover, commercial instruments such as line‐ probe assays or GenoType are also not very useful in the identification of NTM infection to the specific level. Given the American Thoracic Societ recommendation, clinical isolates of NTM should be identified to the species level in order to conduct final diagnosis, determine their clinical significance, appropriate treatment, epidemiological investigation, patient management, and control of infection. Phenotypic identification of NTM species (including growth rate, pigment production, colony morphology, growth in different temperatures, niacin accumulation, nitrate reduction, β‐glucosidase, Tween 80 hydrolysis, arylsulfatase 3‐days, urease, tellurite reduction, catalase, growth on MacConkey agar without crystal violet and tolerance to thiophene‐2‐carboxylic hydrazide, oleate, p‐nitrobenzoic acid, thiacetazone, hydroxylamine, and isoniazid) are time‐consuming, labor‐intensive, expensive, need to be standardized, skillful microbiologist, and in some NTM species are confusing; but molecular methods such as PCR‐restriction fragment length polymorphism (PCR‐RFLP), DNA‐hybridization technique or sequencing using housekeeping genes of 16S rRNA (hypervariable A, positions 125–270 and B, positions 408–503, presence of short helix 18 at positions of 451‐482 in rapidly growing mycobacteria [RGM] or extended helix at positions of 451‐482, which I present in all strain of slowly growing mycobacteria [SGM], ITS [whole length of 16S‐23S rRNA internal transcribe spacer; ITS sequence length in SGM are nearly 75 base pairs shorter than those of RGM strains], rpoB [region V, position 2581‐3300], hsp65 [hypervariable regions positions 624‐664 and positions 683‐725]) are reliable, fast, and inexpensive methods for accurate identification and differentiation of nontuberculosis mycobacteria. Although 16S rRNA is gold‐standard method for identification of unusual mycobacterial species, recent studies was showed that 16S rRNA fail to differentiation of closely related species of NTM species such as Mycobacterium abscessus with M. chelonae and M. avium complex or Mycobacterium farcinogenes with M. senegalense, M. kansasii with M. gastri and M. marinum with M. ulcerans. Furthermore, some species of NTM has two different sets of 16S rRNA gene, which leads to ambiguity in differentiation of NTM. Therefore, the multilocus sequence analysis is essential for accurate identification and differentiation of NTM species. Mycobacterium chelonae sp. is nonchromogenic, acid‐fast, and rapid‐growing mycobacteria, which was introduced by Kubica et al in 1972 from human infection. This bacterium usually grew in slant LJ or liquid Middlebrook 7H11 with smooth–rough variant colonies; M. chelonae complex including M. chelonae subsp. chelonae and M. chelonae subsp. bovis. The standard strain of M. chelonae (ATCC 35752) was phenotypically characterized with a positive result test for niacin accumulation, arylsufatase test (3‐days), heat‐stale catalase, citrate utilization, urea hydrolysis although negative for growth in MacConkey agar without crystal violet, iron uptake from the medium and nitrate reduction test; this species has a unique 16S rRNA and hsp65 signature sequence, which identified to the species level via PCR‐ sequencing of 16S rRNA, hsp65, PCR‐RFLP, whole‐genome sequencing, and high performance liquid chromatography fatty‐acid analysis. This bacterium has greater susceptibility to several antibiotics compared than other RGM. I request the authors to attend the following questions: