IS1245を用いた肺 Mycobacterium avium 症の臨床病型と多クローン性感染の関連についての分子疫学的検討 RELATIONS BETWEEN CLINICAL SUBTYPES OF MYCOBACTERIUM AVIUM PULMONARY DISEASE AND POLYCLONAL INFECTIONS DETECTED BY IS1245 BASED RESTRICTION FRAGMENT LENGTH POLYMORPHISM ANALYSIS
[目的] <I>Mycobacterium avium</I>症の一部の症例は多クローン性感染であることが報告されている。高度な多型性を有するIS1245をマーカーとしたRFLP分析を行い, 肺感染症の臨床像と多クローン性感染の関係について検討した。 [方法] <I>Mycobacterium avium</I>肺感染症を肺結核類似型, 結核後遺症に伴う気管支拡張症型, 中葉舌区型の3群に分類しIS1245を用いたRFLP分析を行った。 [結果] 肺結核類似型と結核後遺症に伴う気管支拡張症型では単クローン性感染が多く長期観察でもクローンの変化を認めない例も存在した。一方, 中葉舌区型は多クローン性感染の頻度が高く, 3種以上の遺伝子型を有する例も認められた。経時的変化を見ると同時多クローン性感染に加えてクローンの交代も認められ, 薬剤感受性の変化からも全く関連のない菌株と考えられた。 [考察] 病型とクローン構成には関連があり, 治療や感受性検査を行う上で多クローン性感染の可能性を考慮する必要があると考えられた。
[Introduction] The epidemiology of <I>Mycobacterium avium-intracellulare</I> (MAC) infections has not been completely defined. Recently some reports presented polyclonal MAC infections. The purpose of this study was to reveal the clonal diversity of <I>Mycobacterium avium</I> isolates and the relation between clinical subtype of lung disease and polyclonal infection.<BR>[Methods] We categorized pulmonary <I>Mycobacterium avium</I> infection to three clinical subtypes, tuberculosis like type, bronchiectasis with preexisting tuberculosis type and nodular bronchiectasis type. <I>Mycobacterium avium</I> isolates of 11 patients were studied for their heterogeneity using 1S1245 based RFLP analysis. The insertion sequence 1S1245 is repetitive element identified only in <I>Mycobacterium avium</I>. Standard method of IS<I>1245</I> based RFLP analysis has been proposed as a suitable technique for typing of <I>Mycobacterium avium</I> isolates for epidemiological and taxonomic studies. At least three distinct colonies were subcultured to single clone. The subclones of the isolates were analyzed by IS<I>1245</I> based RFLP technique and some subclones were also examined by antimicrobial susceptibility test.<BR>[Results] Two of three patients of tuberculosis like type were considered to be monoclonal infection because only a single genotype was identified. And only one of four patients of bronchiectasis with preexisting tuberculosis type was considered to be polyclonal infection despite of long-term observation. Although isolates were collected in two or more occasions in clinical course over one year period, only a single genotype was observed in two patients. In contrast, three of four patients of nodular bronchiectasis type had multiple genotypes. Isolates recovered from patients with monoclonal infection pattern following long-term treatment with clarithromycin monotherapy became resistant to clarithromycin. In contrast, three strains derived from one nodular bronchiectasis patient were susceptible to clarithromycin despite of long-term chemotherapy including clarithromycin. The susceptibility patterns of the other drugs were also apparently different. Strain conversion due to repeated polyclonal infection was considered. These results of the antimicrobial susceptibility test supported clonal diversity of the <I>Mycobacterium avium</I> infection.<BR>[Discussion] IS<I>1245</I> based RFLP analysis possesses a discriminatory power between the isolates on clonal level. This study demonstrates that polyclonal infections are common in nodular bronchiectasis type and monoclonal infections are common in tuberculosis like type and bronchiectasis with preexisting tuberculosis type. And not only simultaneous polyclonal infection but also repeated polyclonal infection were observed in a nodular bronchiectasis type patient.<BR>Drug susceptibility test showed long-term chemotherapy including clarithromycin could change the susceptibility of clarithromycin to resistant in patients with monoclonal infection. In contrast patients with repeated polyclonal infection pattern would avoid drug resistance because of strain conversion. This multiple susceptibility patterns identified in this study would not have been detected by the standard susceptibility test without subculture. And we also need the treatment strategy considering the polyclonal infection.<BR>[Conclusions] Polyclonal infections are considered to be common in pulmonary <I>Mycobacterium avium</I> infection, especially nodular bronchiectasis type. Clonal diversity of <I>Mycobacterium avium</I> infection is an important factor to perform chemotherapy and drug susceptibility test.
結核 79(2), 39-46, 2004-02-15
JAPANESE SOCIETY FOR TUBERCULOSIS