title: Use of mycobacteriophage quantitative PCR on MGIT broths for a rapid tuberculosis antibiogram.
abstract: Phenotypic culture-based drug susceptibility testing (DST) for Mycobacterium tuberculosis is a valuable tool to identify four to six active drugs for individualized multidrug-resistant (MDR) tuberculosis (TB) regimens. Current culture-based methods are slow, however; therefore, we evaluated a rapid mycobacteriophage-based quantitative PCR (qPCR) assay for use directly on M. tuberculosis-positive MGIT broths. We compared phage qPCRs, using a simple cutoff of 3 for the ΔCq value (where Cq is quantification cycle, and ΔCq is calculated as the Cq of starting phage minus the Cq of TB isolates in drug-containing medium), on 325 clinical M. tuberculosis MGIT broth cultures versus the respective subcultured isolates tested by agar proportion. The median accuracy for the 13 drugs/concentrations tested was 98%, with most discrepancies being false-resistant results. Evaluation of phage qPCR on greater numbers of resistant strains of 393 isolates grown on Löwenstein-Jensen medium showed similar findings, with a median accuracy, sensitivity, and specificity of 97%, 90%, and 99%, respectively. This rapid culture-based DST methodology can be performed for any drug on TB-positive MGIT broths, with a specimen-to-antibiogram turnaround time of approximately 23.9 days, compared with waiting 58.6 days for isolate growth on solid medium followed by agar proportion DST.
authors.affiliation: Department of Microbiology, Faculty of Medicine, Siriraj Hospital, Mahidol University, Bangkok, Thailand.
authors.forename: Suporn
authors.initials: S
authors.lastname: Foongladda
authors.forename: Wiphat
authors.initials: W
authors.lastname: Klayut
authors.forename: Rattapha
authors.initials: R
authors.lastname: Chinli
authors.forename: Suporn
authors.initials: S
authors.lastname: Pholwat
authors.forename: Eric R
authors.initials: ER
authors.lastname: Houpt
mesh_terms: D000995:Antitubercular Agents / Q000494:pharmacology; D003470:Culture Media / Q000378:metabolism; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods*; D009160:Mycobacteriophages / Q000187:drug effects / Q000235:genetics*; D009169:Mycobacterium tuberculosis / Q000187:drug effects / Q000821:virology*; D016133:Polymerase Chain Reaction / Q000379:methods; D012680:Sensitivity and Specificity; D018088:Tuberculosis, Multidrug-Resistant / Q000188:drug therapy / Q000382:microbiology / Q000821:virology
chemical_list: D000995:Antitubercular Agents; D003470:Culture Media