Rapid assessment of mycobacterial growth inside macrophages and mice, using the radiometric (BACTEC) method

Abstract

Setting: Conventional methods of determining the growth and drug susceptibility of mycobacteria either in macrophages or in vivo are time consuming and laborious.

Objective: We sought to develop a simple and rapid method for assessing growth and susceptibility of mycobacteria in macrophages and in vivo.

Design: The radiometric (BACTEC) method was compared with the conventional method for rapid assessment of growth and susceptibility of Mycobacterium avium complex (MAC) to clofazimine (CFM) and its two analogues (B4100 and B4101) in macrophages and in beige mice.

Results and conclusions: A linear relationship was observed between growth index (GI) readings by the BACTEC method and the colony forming unit (CFU) counts obtained by conventional plating on 7H11 agar in vitro of lysates from infected macrophages and of homogenates from the infected organs. There was also a good agreement between the two methods with respect to susceptibility of MAC to CFM and its analogues both in macrophages and in spleen. The BACTEC method, in addition to being quick and simple, was found to be more consistent. Our studies thus demonstrate that the radiometric method has potential application in rapid screening of drugs for antimycobacterial activity in macrophages and in animals besides its established value in in vitro screening.