Non-Invasive Mycobacterium avium Detection Using ^99mTc-GSA on Single-Photon Emission Computed Tomography

Background: The prevalence of nontuberculous mycobacteria (NTM) infection is on the rise, surpassing that of pulmonary tuberculosis in Japan. Current standard therapy for NTM infection involves long-term treatment of at least 1.5 years, with low success rates and a high relapse rate. ^99mTc-diethylenetriaminepentaacetic acid-galactosyl-human serum albumin (^99mTc-GSA) is used for human liver imaging. In this study, we utilized ^99mTc-GSA as a probe to detect Mycobacterium avium (M. avium), a major pathogen in NTM pulmonary diseases (NTM-PDs). Our aim was to investigate the non-invasive detection of M. avium using ^99mTc-GSA on Single-Photon Emission Computed Tomography (SPECT). Methods: The accumulation of ^99mTc-GSA in M. avium was investigated in vitro. In vivo, SPECT images were obtained after the administration of ^99mTc-GSA to an M. avium thigh infection model. Subsequently, the contrast difference in accumulated ^99mTc-GSA between infected and non-infected thighs was calculated using SPECT imaging. Furthermore, SPECT images were obtained for thighs infected with varying bacterial loads, and the accumulation was compared between them. Results: In vitro, we observed that ^99mTc-GSA accumulates in M. avium. In vivo, SPECT images demonstrated the specific accumulation of ^99mTc-GSA at the infection site, with this accumulation being correlated with the bacterial load. Conclusions: ^99mTc-GSA specifically accumulates in M. avium, and SPECT can be used to monitor the distribution and quantity of M. avium in animals. By utilizing these measures, ^99mTc-GSA can be targeted to the site of infection and used as a bacterial probe.