Diagnostic predictive values of the hain genotype MTBDRsl assay in mycobacterial strains isolated from Sudan

Abstract

Introduction: hain GenoType MTBDRsl is nucleic acid amplification assay based on reverse hybridization with specific oligonucleotide probes on nitrocellulose strips. MTBDRsl identifies M. tuberculosis complex and detects resistance to fluoroquinolone, second line injectable drugs and ethambutol evident as mutations of gyrA, rrs and embB genes respectively. This study aimed to evaluate the diagnostic performance of the Hain GenoType MTBDRsl Assay using 1% proportion method on LJ medium as gold standard.

Methods: a total of 52 rifampicin resistant (RR) isolates were tested for second line drug sensitivity by 1% proportion method and by MTBDRsl assay.

Results: two strains were identified as mycobacteria other than tuberculosis MOTT and the rest were Mycobacterium tuberculosis complex MTBC. Five of the MTBC isolates (5/50; 10%) showed resistance to at least one second line drug and one isolate (1/50; 2%) was XDR. XDR strain was concordantly detected by the two methods. One of two Kanamycin-resistant isolates showed discordant result. Ofloxacin showed one false positive and one false negative result. Most discrepancies were detected with Ethambutol. The sensitivity, specificity, positive and negative predictive values were respectively as follows: Ethambutol (63.3.4%, 85.7%, 94.4% and 62%): for Kanamycin (67%, 100%, 100% and 97.9%): for Amikacin and Capreomycin (100%, 100%, 100% and 100%): for Ofloxacin (75%, 97.5%, 75% and 97.8%). For XDR isolate the values were (100%, 100%, 100% and 100%) respectively.

Conclusion: MTBDRsl showed high specificity and negative predictive values making it acceptable and time-saving for early presumptive detection of resistance to second-line drugs in Sudan.