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Journal of Clinical Microbiology, October 1998, p. 2940-2943, Vol. 36, No. 10
Department of Pathology, University of Texas
Medical Branch, Galveston, Texas 77555-0740.
Received 25 March 1998/Returned for modification 25 May
1998/Accepted 1 July 1998
The reliability of the ESP Culture System II (herein referred to as
ESP II) for testing susceptibilities of Mycobacterium tuberculosis isolates to isoniazid, rifampin, ethambutol, and streptomycin was evaluated by comparing results to those of the method
of proportion (MOP), which was considered the reference method, for 20 clinical isolates and 30 challenge strains provided by the Centers for
Disease Control and Prevention (CDC). Clinical isolates also were
tested with the BACTEC TB 460 system; these results agreed with those
obtained by the MOP for all isolates and all drugs, except the high
concentration of isoniazid, for which agreement was 95%. After
resolution of discrepancies, levels of agreement between ESP II and MOP
for the clinical isolates were 95 and 100%, respectively, for the low
and high concentrations of isoniazid, 100% for rifampin and
ethambutol, and 95% for streptomycin. For the 30 challenge isolates,
ESP II results for both concentrations of isoniazid agreed with the
expected results in all cases, whereas agreement was 93% for both
rifampin and streptomycin and 90% for ethambutol. All discrepancies
with the CDC isolates were due to failure of ESP II to correctly
classify resistant strains. By testing isolates yielding discrepant
ethambutol and streptomycin results with a lower concentration of both
drugs in the ESP II system, agreement increased to 93% for ethambutol
and 100% for streptomycin. For the clinical isolates, the times to an
ESP II result of susceptible (means ± standard errors of the
means) were 8.47 ± 0.12 days (range, 7 to 10 days) and 8.73 ± 0.29 days (range, 5 to 11 days) when the inoculum was prepared from
a McFarland equivalent and from a seed bottle, respectively. The time
to an ESP II result of resistant varied by drug and method of
inoculum preparation, ranging from 5.50 ± 0.22 days for
ethambutol with the inoculum prepared from a McFarland standard to 8.0 days for ethambutol with the inoculum prepared from a seed bottle.
These data suggest that the ESP II system is a rapid and reliable
method for testing susceptibilities of M. tuberculosis
isolates to isoniazid and rifampin. Performance, however, may be
suboptimal for ethambutol and streptomycin. Testing additional
ethambutol-resistant and streptomycin-resistant strains with two
concentrations of both drugs is necessary.
0095-1137/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Evaluation of the ESP Culture System II for Testing
Susceptibilities of Mycobacterium tuberculosis Isolates
to Four Primary Antituberculous Drugs
*
Corresponding author. Mailing address: Department of
Pathology, University of Texas Medical Branch, Galveston, TX
77555-0740. Phone: (409) 772-4851. Fax: (409) 772-5683. E-mail:
gwoods{at}utmb.edu.
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