Determination of ethambutol MICs for Mycobacterium tuberculosis and Mycobacterium avium isolates by resazurin microtitre assay.
OBJECTIVE
To test susceptibilities of Mycobacterium tuberculosis (MTB) isolates to ethambutol by the Löwenstein-Jensen (LJ) proportion method and resazurin microtitre assay (REMA) and to evaluate REMA for the determination of ethambutol MICs for MTB and Mycobacterium avium isolates.


METHODS
A total of 50 MTB and 20 M. avium isolates were tested to determine the MICs of ethambutol by REMA and agar dilution method. MTB isolates were also tested by the LJ proportion method.


RESULTS
REMA provided ethambutol susceptibility results for all the isolates within 8-9 days. For MTB isolates, REMA showed 96.7% sensitivity, 100.0% specificity and 98.0% accuracy when LJ proportion results were taken as 'gold standard'. For both MTB and M. avium isolates, the MICs determined by REMA were lower than those determined in agar medium, indicating that MIC values determined by REMA are closer to the actual MICs for the isolates.


CONCLUSIONS
REMA can be used as a rapid and inexpensive method for mycobacterial drug susceptibility testing against ethambutol. In comparison with the agar method, the MICs determined by REMA can more accurately be correlated with achievable plasma concentrations of antimycobacterial agents.
Jadaun
G P S
GP
Department of Microbiology and Molecular Biology, National JALMA Institute for Leprosy and Other Mycobacterial Diseases (Indian Council of Medical Research), PO Box 1101, Dr M. Miyazaki Marg, Tajganj, Agra 282001, India.
Agarwal
Chhaya
C
Sharma
Hirdesh
H
Ahmed
Zafar
Z
Upadhyay
Prashant
P
Faujdar
Jaya
J
Gupta
Anuj Kumar
AK
Das
Ram
R
Gupta
Pushpa
P
Chauhan
D S
DS
Sharma
V D
VD
Katoch
V M
VM
D000995:Antitubercular Agents / Q000494:pharmacology*; D003470:Culture Media; D004783:Environmental Microbiology; D004977:Ethambutol / Q000494:pharmacology*; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods; D015269:Mycobacterium avium Complex / Q000187:drug effects*; D009169:Mycobacterium tuberculosis / Q000187:drug effects*; D010078:Oxazines / Q000378:metabolism*; D012680:Sensitivity and Specificity; D014397:Tuberculosis, Pulmonary / Q000382:microbiology; D014966:Xanthenes / Q000378:metabolism*
D000995:Antitubercular Agents; D003470:Culture Media; D010078:Oxazines; D014966:Xanthenes; C005843:resazurin; D004977:Ethambutol