[Relations between clinical subtypes of Mycobacterium avium pulmonary disease and polyclonal infections detected by IS1245 based restriction fragment length polymorphism analysis].

INTRODUCTION

The epidemiology of Mycobacterium avium-intracellulare (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 Mycobacterium avium isolates and the relation between clinical subtype of lung disease and polyclonal infection.

METHODS

We categorized pulmonary Mycobacterium avium infection to three clinical subtypes, tuberculosis like type, bronchiectasis with preexisting tuberculosis type and nodular bronchiectasis type. Mycobacterium avium isolates of 11 patients were studied for their heterogeneity using IS1245 based RFLP analysis. The insertion sequence IS1245 is repetitive element identified only in Mycobacterium avium. Standard method of IS1245 based RFLP analysis has been proposed as a suitable technique for typing of Mycobacterium avium isolates for epidemiological and taxonomic studies. At least three distinct colonies were subcultured to single clone. The subclones of the isolates were analyzed by IS1245 based RFLP technique and some subclones were also examined by antimicrobial susceptibility test.

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 Mycobacterium avium infection.

DISCUSSION

IS1245 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. 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.

CONCLUSIONS

Polyclonal infections are considered to be common in pulmonary Mycobacterium avium infection, especially nodular bronchiectasis type. Clonal diversity of Mycobacterium avium infection is an important factor to perform chemotherapy and drug susceptibility test.