Last data update: Jun 24, 2024. (Total: 47078 publications since 2009)
Records 1-2 (of 2 Records) |
Query Trace: Tyrrell FC [original query] |
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Using reduced inoculum densities of Mycobacterium tuberculosis in MGIT Pyrazinamide Susceptibility Testing to prevent false-resistant results and improve accuracy: A multicenter evaluation
Morlock GP , Tyrrell FC , Baynham D , Escuyer VE , Green N , Kim Y , Longley-Olson PA , Parrish N , Pennington C , Tan D , Austin B , Posey JE . Tuberc Res Treat 2017 2017 3748163 The primary platform used for pyrazinamide (PZA) susceptibility testing of Mycobacterium tuberculosis is the MGIT culture system (Becton Dickinson). Since false-resistant results have been associated with the use of this system, we conducted a multicenter evaluation to determine the effect of using a reduced cell density inoculum on the rate of false resistance. Two reduced inoculum densities were compared with that prescribed by the manufacturer (designated as "BD" method). The reduced inoculum methods (designated as "A" and "C") were identical to the manufacturer's protocol in all aspects with the exception of the cell density of the inoculum. Twenty genetically and phenotypically characterized M. tuberculosis isolates were tested in duplicate by ten independent laboratories using the three inoculum methods. False-resistant results declined from 21.1% using the standard "BD" method to 5.7% using the intermediate ("A") inoculum and further declined to 2.8% using the most dilute ("C") inoculum method. The percentages of the resistant results that were false-resistant declined from 55.2% for the "BD" test to 28.8% and 16.0% for the "A" and "C" tests, respectively. These results represent compelling evidence that the occurrence of false-resistant MGIT PZA susceptibility test results can be mitigated through the use of reduced inoculum densities. |
Probability of negative Mycobacterium tuberculosis complex cultures based on time-to-detection of positive cultures: a multi-center evaluation of commercial broth-based culture systems
Tyrrell FC , Budnick GE , Elliott T , Gillim-Ross L , Hildred MV , Mahlmeister P , Parrish N , Pentella M , Vanneste J , Wang YF , Starks AM . J Clin Microbiol 2012 50 (10) 3275-82 We conducted a multicenter study to determine whether Mycobacterium tuberculosis complex (MTBC) cultures in automated broth-based systems could reliably be considered as negative sooner than six weeks. Laboratory sites used MGIT or BacT/ALERT and tracked results of time to detection of mycobacteria (TTD-all, n = 1547) and MTBC (TTD-MTBC, n = 466) over six-month periods from primarily (93%) respiratory specimens. Cumulative percentages by day detected and median TTD of initial and follow-up specimens were analyzed. The median TTD-MTBC for MGIT (n = 6 sites) was 14 days. For laboratories using standard processing procedures, 100% of MTBC were detected from initial and follow-up specimens in 28 and 35 days, respectively, and no yield of MTBC on solid or MGIT liquid media was observed after five weeks. The median TTD-MTBC for BacT/ALERT (n = 3 sites) was 18 days, with 95% and 100% detected within 37 and 42 days respectively. Analysis of TTD of positive MTBC cultures in broth can predict the probability of culture negativity at defined time points. Receipt of interim negative reports earlier than six weeks could assist clinicians in considering alternative diagnoses, and could alter timing and prioritization of public health interventions. Laboratories should analyze their own TTD data to inform protocol decisions. Laboratories using MGIT could issue no growth of MTBC reports on initial specimens as early as four weeks and on patients undergoing treatment as early as five weeks post-inoculation. |
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