Antibiotic Susceptibility and Genotyping of Mycobacterium avium Strains That Cause Pulmonary and Disseminated Infection

Mycobacterium avium subsp.hominissuis mainly causes disseminated infection in immunocompromised hosts, such as individuals with human immunodeficiency virus (HIV) infection, and pulmonary infection in immunocompetent hosts. However, many aspects of the different types ofM. avium subsp.hominissuis infection remain unclear. We examined the antibiotic susceptibilities and genotypes ofM. avium subsp.hominissuis isolates from different hosts by performing drug susceptibility testing using eight antibiotics (clarithromycin, rifampin, ethambutol, streptomycin, kanamycin, amikacin, ethionamide, and levofloxacin) and variable-number tandem-repeat (VNTR) typing analysis for 46 isolates from the sputa of HIV-negative patients with pulmonaryM. avium subsp.hominissuis disease without previous antibiotic treatment and 30 isolates from the blood of HIV-positive patients with disseminatedM. avium subsp.hominissuis disease. Interestingly, isolates from pulmonaryM. avium subsp.hominissuis disease patients were more resistant to seven of the eight drugs, with the exception being rifampin, than isolates from HIV-positive patients. Moreover, VNTR typing analysis showed that the strains examined in this study were roughly classified into three clusters, and the genetic distance from reference strain 104 for isolates from pulmonaryM. avium subsp.hominissuis disease patients was statistically significantly different from that for isolates from HIV-positive patients (P = 0.0018), suggesting thatM. avium subsp.hominissuis strains that cause pulmonary and disseminated disease have genetically distinct features. Significant differences in susceptibility to seven of the eight drugs, with the exception being ethambutol, were noted among the three clusters. Collectively, these results suggest that an association between the type ofM. avium subsp.hominissuis infection, drug susceptibility, and the VNTR genotype and the properties ofM. avium subsp.hominissuis strains associated with the development of pulmonary disease are involved in higher levels of antibiotic resistance.