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Journal of Clinical Microbiology, April 2000, p. 1498-1501, Vol. 38, No. 4
National Jewish Medical and Research Center,
Denver, Colorado
Received 3 September 1999/Returned for modification 27 December
1999/Accepted 25 January 2000
A new agar medium to perform pyrazinamide (PZA) susceptibility
testing with Mycobacterium tuberculosis has been developed. This medium has an acidic pH of 6.0 instead of the usual for agar media, pH 6.8, to provide optimal conditions for PZA activity, and it
also differs from conventional Middlebrook 7H10/7H11 agar in that
animal serum (fetal or calf bovine or fetal equine serum) is used
instead of oleic acid-albumin-dextrose-catalase to support good growth
of M. tuberculosis at the low pH of 6.0. A critical concentration of 900 or 1,200 µg of PZA/ml in this medium made it
possible to differentiate between PZA-susceptible and PZA-resistant clinical isolates. This agar medium has the following advantages compared to a liquid medium: it allows determination of the actual proportion of PZA-resistant bacteria in the isolate and it is simple
and inexpensive. In addition, it has the potential of being used for a
direct susceptibility test with PZA, but this approach will require
further confirmation. Further studies to develop critical
concentrations of other drugs for this low-pH medium, as well as to
investigate the possibility of cultivation in regular (non-CO2) incubators, are in progress.
0095-1137/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
New Agar Medium for Testing Susceptibility of
Mycobacterium tuberculosis to Pyrazinamide
*
Corresponding author. Mailing address: 1400 Jackson
St., Denver, CO 80206. Phone: (303) 398-1384. Fax: (303)
398-1953. E-mail: heifetsl{at}njc.org.
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