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No. 58 (PM 7)
Mycobacterium Kyorinense Infection: Clinical Features and Antimicrobial
Susceptibility
Hiroaki Ohnishi 1 , Shota Yonetani 1 , Satsuki Matsushima 1 , Kouki Ohtsuka 1 , Tomonori
Kishino 1 , Hiroo Wada 2 , Hajime Goto 2 , Takashi Watanabe 1
Departments of 1 Laboratory Medicine and 2 Respiratory Medicine, Kyorin University
School of Medicine, Japan
Mycobacterium kyorinense is a nonpigmented, slowly growing mycobacterium that was initially
isolated in 2007. Biochemical tests and genetic analyses showed that M. kyorinense is most closely
related to M. celatum and M. branderi. We here describe 7 newly identified cases with 4 previously
reported cases, in which infection potentially was caused by M. kyorinense. In reviewing these 11 cases
(10 Japanese and 1 Brazilian), 9 presented with respiratory infections, 1 with lymphadenitis, and 1 with
arthritis. Seven patients were treated by first-line tuberculosis drugs, mainly consisting of rifampin,
isoniazid, and ethambutol, but these therapies were ineffective in all cases. Six cases were treated with a
combination of antibiotics including macrolides and fluoroquinolones as a first- or second-line
chemotherapy, and infection was subdued without recurrence in 5 cases. In contrast, 4 pneumonia
patients who did not receive sufficient therapy with the latter regimen eventually died of infection. In
concordance with the clinical antimicrobial susceptibility, most strains exhibited relatively high MICs
for rifampin, ethambutol, and isoniazid, and relatively low MICs for macrolides, aminoglycosides, and
quinolones. Notably, remarkably high MICs (>32 �g/ml) w
Direct sequencing of the 16S rRNA gene revealed that all available M. kyorinense isolates were
identical within this gene, except for the Brazilian strain which showed slight difference with other
Japanese isolates. Direct sequencing of the entire rpoB gene demonstrated that all strains had identical
sequences, with Ser531 in the M. tuberculosis RpoB protein replaced by an Asp in M. kyorinense.
Notably, Ser531 is the most frequent location of substitutions in rifampin-resistant strains of M.
tuberculosis. These data suggest that M. kyorinense belongs to non-tuberculous mycobacteria that have
pathogenicity for humans with substantial clinical significance, and that M. kyorinense is inherently
resistant to rifampin due to the structural features of its RpoB protein.
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