Abstract
BackgroundThe incidence of multidrug-resistant tuberculosis (MDR-TB) is increasing and the emergence of extensively drug-resistant tuberculosis (XDR-TB) is a major challenge. Controlling resistance, reducing transmission and improving treatment outcomes in MDR/XDR-TB patients is reliant on susceptibility testing. Susceptibility testing using phenotypic methods is labour intensive and time-consuming. Alternative methods, such as molecular assays are easier to perform and have a rapid turn-around time. The World Health Organization (WHO) has endorsed the use of line probe assays (LPAs) for first and second line diagnostic screening of MDR/XDR-TB.MethodsWe compared the performance of LPAs to BACTEC MGIT 960 system for susceptibility testing of bacterial resistance to first-line drugs: rifampicin (RIF), isoniazid (INH), ethambutol (EMB), and second-line drugs ofloxacin (OFL) and kanamycin (KAN). One hundred (100) consecutive non-repeat Mycobacterium tuberculosis cultures, resistant to either INH or RIF or both, as identified by BACTEC MGIT 960 were tested. All isoniazid resistant cultures (n = 97) and RIF resistant cultures (n = 90) were processed with Genotype®MTBDRplus and Genotype®MTBDRsl line probe assays (LPAs). The agar proportion method was employed to further analyze discordant LPAs and the MGIT 960 isolates.ResultsThe Genotype ®MTBDRplus (version 2) sensitivity, specificity, PPV and NPV from culture isolates were as follows: RIF, 100%, 87.9, 58.3% and 100%; INH, 100%, 94.4%, 93.5% and 100%. The sensitivity, specificity PPV and NPV for Genotype ® MTBDRsl (version 1 and 2) from culture isolates were as follows: EMB, 60.0%, 89.2%, 68.2% and 85.3%; OFL, 100%, 91.4%, 56.2% and 100%; KAN, 100%, 97.7%, 60.0% and 100%. Line probe assay showed an excellent agreement (k = 0.93) for INH susceptibility testing when compared to MGIT 960 system while there was good agreement (k = 0.6–0.7) between both methods for RIF, OFL, KAN testing and moderate agreement for EMB (k = 0.5). A high RIF mono-resistance (MGIT 960 33/97 and LPA 43/97) was observed.ConclusionLPAs are an efficient and reliable rapid molecular DST assay for rapid susceptibility screening of MDR and XDR-TB. Using LPAs in high MDR/XDR burden countries allows for appropriate and timely treatment, which will reduce transmission rates, morbidity and improve treatment outcomes in patients.
Highlights
The incidence of multidrug-resistant tuberculosis (MDR-TB) is increasing and the emergence of extensively drug-resistant tuberculosis (XDR-TB) is a major challenge
We compared the performance of molecular line probe assay to Mycobacterium growth indicator tube (MGIT) 960 system for the detection of resistance to first- and second-line drugs. Study design This was a prospective descriptive study comparing the performance of the Line probe assay (LPA) (Hain Lifescience, Nehren, Germany) to BACTEC MGIT 960 system (Becton Dickinson Microbiology System, Sparks, MD, USA) for susceptibility testing of first and second-line anti-TB drugs
First line drug susceptibility testing (DST) A total of 100 cultures were analyzed in this study of which 97 were viable after subculture (Fig. 1)
Summary
The incidence of multidrug-resistant tuberculosis (MDR-TB) is increasing and the emergence of extensively drug-resistant tuberculosis (XDR-TB) is a major challenge. Controlling resistance, reducing transmission and improving treatment outcomes in MDR/XDR-TB patients is reliant on susceptibility testing. Susceptibility testing using phenotypic methods is labour intensive and time-consuming. Alternative methods, such as molecular assays are easier to perform and have a rapid turn-around time. In 2015, 480,000 cases of MDR-TB were estimated globally, with 10,000 of those occurring in South Africa [1]. Absent detection of drugresistant TB may result in treatment failure and the development of extensively drug resistant TB (XDR-TB). XDR-TB has been reported in about 117 countries and globally, 9.5% of MDR-TB cases have developed XDR-TB. The TB burden can only be reduced by speeding up detection rates and identifying treatment gaps [1]
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