Mycobacterium avium Complex (MAC) is a group of opportunistic non-tuberculous mycobacterial species (NTM) which includes M. avium and M. intracellulare. MAC organisms, particularly M. intracellulare, are a significant cause of pulmonary infections in older patients, often in the presence of underlying lung disease. When compared with M. avium, M. intracellulare is more often isolated from immuno-competent patients. The disease may be an infection with the same organism or chronic disease with multiple strains. Re-infection following treatment can occur. As the source of the infections is environmental, there is the potential for ongoing infections with multiple genotypes as well as colonisation without disease. Treatment of NTM disease is problematic because of the resistant nature of the organisms.
Does repeated isolation of the organism indicate a chronic infection with the same genotype or re-infection with a different genotype? Is the strain associated with significant disease or does it represent colonisation? This information would help to target antibiotic therapy or avoid further costly investigations and treatment. By comparing environmental and patient isolates there would also be the possibility of determining the potential source of the infection. Do some strains have characteristics which predispose patients to chronic infection and disease? Are there preventative measures the patient could take to prevent infection? A genotyping strategy would enable clinicians to understand the nature of infection of M. intracellulare in a patient M. intracellulare is the most common NTM isolated in respiratory isolates in QLD. The incidence of infections due to M. intracellulare is increasing both in QLD and worldwide. This preliminary study investigated the use of a 7-loci MIRU-VNTR genotyping method using a random selection of clinical isolates of M. intracellulare. The results showed a discriminatory method suitable for further investigation of both clinical and environmental isolates of M. intracellulare.