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Journal of Clinical Microbiology, November 1999, p. 3528-3532, Vol. 37, No. 11
PHLS Mycobacterium Reference Unit, Dulwich
PHL and Department of Microbiology, King's College School of Medicine
and Dentistry, King's College Hospital (Dulwich), London SE22 8QF,
United Kingdom
Received 24 May 1999/Returned for modification 28 June
1999/Accepted 19 July 1999
Rapid molecular assays for the detection of mutations associated
with rifampin resistance in Mycobacterium tuberculosis are commercially available. However, they are complex and expensive and
have predictive values of 90 to 95%. Molecular assays for other drugs
are less predictive of resistance. Ideally, assays based on phenotypic
markers should be used for susceptibility testing, but these can take
weeks to complete. We previously described a rapid phenotypic assay,
the phage amplified biologically (PhaB) assay, for the rapid
determination of rifampin and isoniazid susceptibility in clinical
isolates of M. tuberculosis. In this study, we extended the
assay to the study of ethambutol, pyrazinamide, streptomycin, and
ciprofloxacin. After the optimization of antibiotic concentrations and
incubation conditions, the assay was applied to each drug for a total
of 157 isolates. The correlations between the results of the PhaB assay
and the resistance ratio method were 94% for isoniazid, 96% for
streptomycin, 100% for ciprofloxacin, 88% for ethambutol, and 87%
for pyrazinamide. For ciprofloxacin, ethambutol, and pyrazinamide,
significantly better correlations were found when a 90% reduction in
plaque count was used as the cutoff. Turnaround times for the PhaB
assay were 2 to 3 days, compared with 10 days for the resistance ratio
method. We believe that this low-cost assay may have widespread
applicability for the rapid screening of drug resistance in M. tuberculosis isolates, especially in developing countries.
0095-1137/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Evaluation of a Bacteriophage-Based Assay (Phage
Amplified Biologically Assay) as a Rapid Screen for Resistance to
Isoniazid, Ethambutol, Streptomycin, Pyrazinamide, and
Ciprofloxacin among Clinical Isolates of Mycobacterium
tuberculosis
*
Corresponding author. Mailing address: PHLS
Mycobacterium Reference Unit, Dulwich PHL and Department of
Microbiology, King's College School of Medicine and Dentistry, King's
College Hospital (Dulwich), East Dulwich Grove, London SE22 8QF, United
Kingdom. Phone: 0181-693-1312. Fax: 0171-346-6477. E-mail:
ijelt{at}aol.com.
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