Flow cytometric testing of susceptibilities of Mycobacterium avium to amikacin, ciprofloxacin, clarithromycin and rifabutin in 24 hours


Corresponding author and reprint requests: R. F. Schell, Wisconsin State Laboratory of Hygiene, University of Wisconsin, 465 Henry Mall, Madison, WI 53706, USA
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Objective  To develop a biologically safe flow cytometric susceptibility test that depends on detection and enumeration of actively growing Mycobacterium avium organisms in drug-free and antimycobacterial agent-containing medium.

Methods  Prior to analysis by flow cytometry, all M. avium susceptibility test samples were inactivated by exposure to paraformaldehyde. The susceptibilities of 20 clinical isolates of M. avium to amikacin, ciprofloxacin, clarithromycin, and rifabutin were tested by the flow cytometric and BACTEC methods.

Results  Agreement was 97% between the results of the two methods. The results of flow cytometric susceptibility tests were available 24 h after inoculation of drug-containing medium, while the BACTEC method required 4–8 days to complete.

Conclusions  The flow cytometric assay is safe, simple and reproducible.