title: 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.
abstract: 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.
authors.affiliation: 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. ijelt@aol.com
authors.forename: I J
authors.initials: IJ
authors.lastname: Eltringham
authors.forename: S M
authors.initials: SM
authors.lastname: Wilson
authors.forename: F A
authors.initials: FA
authors.lastname: Drobniewski
mesh_terms: D000995:Antitubercular Agents / Q000494:pharmacology*; D002939:Ciprofloxacin / Q000494:pharmacology; D004352:Drug Resistance, Microbial / Q000235:genetics; D004977:Ethambutol / Q000494:pharmacology; D005069:Evaluation Studies as Topic; D006801:Humans; D007538:Isoniazid / Q000494:pharmacology; D008826:Microbial Sensitivity Tests / Q000379:methods*; D009160:Mycobacteriophages; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification; D010641:Phenotype; D011718:Pyrazinamide / Q000494:pharmacology; D013307:Streptomycin / Q000494:pharmacology; D014376:Tuberculosis / Q000188:drug therapy / Q000382:microbiology
chemical_list: D000995:Antitubercular Agents; D011718:Pyrazinamide; D002939:Ciprofloxacin; D004977:Ethambutol; D007538:Isoniazid; D013307:Streptomycin