Evaluation of the Sensititre® MYCOTB MIC plate for susceptibility testing of Mycobacterium tuberculosis against the Etest and Agar proportion methods
International Journal of Infectious Diseases
The introduction of the Sensititre® MYCOTB MIC plate a microtitre plate containing lyophilized antibiotics and configured for the determination of minimum inhibitory concentration to first and second line anti-tuberculosis drugs can change the laborious methods currently used for drug susceptibility testing. At present reputable procedures for susceptibility testing of M. tuberculosis categorize clinical isolates as either drug resistant or drug susceptible due to their ability to grow in the
... esence of mostly single critical concentration despite of whether high level, moderate level or low level drug resistance is present. The limited scientific background for critical concentrations used for particularly second-line drugs is especially problematic. The determination of M. tuberculosis susceptibility testing using MICs instead of use of critical concentration will be one of the first in South Africa. However, the performance of the Sensititre plate has not been compared to methods that uses MICs for susceptibility testing the agar proportion method and Etest. Objective: To evaluate Sensititre® MYCOTB MIC plate performance against agar proportion (APM) and Etest methods Methods & Materials: Seventy-five M. tuberculosis isolates were included in the study. Isolates were collected from the Drug Resistance survey currently being carried out in South Africa since 2012. The full spectrum of resistance from mono-resistance and poly-resistance through MDRTB, to pre-XDRTB and XDRTB.were included in the study. MICs categorical and essential agreements (± 1dilution from critical concentration) were compared of the microtitre Sensititre MYCOTB plate method against the agar proportion and the Etest methods. Results: Essential agreement between Sensititre plate and APM with respect to susceptible or resistant was 92% for 10 of 11 drugs and 96% by categorical agreement. For ethambutol, essential agreement was 80-81%. while for moxifloxacin, agreement was 83-85%. Categorical agreement between Etest and APM methods was 100% for rifampin, ethambutol, streptomycin, and ofloxacin and 98% for isoniazid. They was a high rate of contamination with Etest which warranted many repeats. For MYCOTB and Etest, median time to plate interpretation was 10 days while APM it was 21 days. Conclusion: The Sensititre method provides a more rapid, quantitative, and efficient method with no test failures due to contamination for both first-and second-line drugs when compared to the APM and Etest.