We developed two colorimetric methods for the detection of vancomycin-and oxacillin-resistant Staphylococcus aureus in <6 h: (i) a nitrate reductase assay and (ii) a resazurin microplate method. MICs agreed with results obtained by CLSI methods for oxacillin. However, detection of vancomycin resistance required a larger inoculum. These methods may be recommended for the detection of vancomycin-and oxacillin-resistant S. aureus.
Multi-drug resistant (MDR) Mycobacterium tuberculosis is still a serious public health problem all over the world. MDR tuberculosis (MDR-TB) caused by these strains has emerged within the last decade and rapid detection is critical for the effective treatment of patients. Recently, a resazurin microtiter assay plate for detecting MDR strains was developed. In this study, it was adapted to screw-cap tubes and the activity of isoniazid (INH) and rifampin (RIF) to 50 M. tuberculosis clinical isolates was tested by this method for the first time. Results were compared with the radiometric reference method for the susceptibility testing of M. tuberculosis complex. The results of both methods were in 100% and 96% agreement for RIF and INH, respectively. Specificity, sensitivity, positive predictive value and negative predictive value were 91.7%, 100%, 92.8% and 100% for INH, respectively. All of these values were 100% for RIF. Susceptibility testing results were obtained on the 8th day of incubation for 42 isolates and on the 9th day for the other eight strains. Our results indicate that this method is suitable for the early determination of INH and RIF resistance in developing countries because it is inexpensive, rapid and easy to perform.
Rapid detection of drug resistance by the direct NRA on sputum smear-positive samples was accurate and easy to implement in clinical diagnostic laboratories, making it a good alternative for rapid screening for MDR and XDR tuberculosis.
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