Line-Probe Assay (LPA) and 96-well – new platforms for resistance
TB remains a public health threat requiring global commitments. According to the WHO report in 2020 only 59% of drug-resistant TB cases were treated successfully. The most important obstacles to controlling TB are delayed identification of drug resistance corresponding to inappropriate clinical management and transmission of resistant strains through the community and hospital settings. Conventional methods for detecting drug resistance have a long turnaround time because they are based on mycobacterial culture isolation on liquid or solid media followed by visual assessment of M. tuberculosis growth under critical concentration or minimum inhibitory concentration of anti-TB medicines. However, clinicians need to make treatment decisions at the time of verification of the diagnosis. On the other hand, prescribing empirical or standardised treatment prior to drug susceptibility test results in high drug-resistant TB countries significantly increases the risk of interruption (no expected effect or even deterioration of condition despite treatment initiation), treatment failure (delayed sputum conversion, reduced adherence to treatment, etc) and nosocomial spreading in case of limited infection control.
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One of the key principles of modern laboratory diagnostics of social significant infectious diseases, such as TB, is taking into consideration not only the diagnostic accuracy of the test but also the level of complexity to guide implementation. The line-probe assay (LPA) manufactured by Autoimmun Diagnostika (AID) GmbH (GenID, Straßberg, Germany) has three commercially available LPA modules. The first module is used to detect Wild Type (WT) and specific mutations associated with isoniazid (katG and inhA promoter), Rifampicin (rpoB), and Prothionamide/Ethionamide (inhA promoter) resistance. The second module (FQ-E) is used to detect WT and specific mutations associated with levofloxacin/moxifloxacin (gyrA) and ethambutol (embB) resistance. The third module (AG) is used to detect WT and specific mutations associated with aminoglycosides Amicacine, Kanamycin, Streptomycin (rpsL and rrs) and polypeptide Capreomycin (rrs) resistance.
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The LPA should be considered as the initial rapid molecular test to detect TB and antibiotic resistance to the most important anti-TB drugs, directly from sputum samples, within one working day. LPA modules (AID GmbH) were investigated in Ukraine during operational research. We evaluated the complexity, diagnostic accuracy and clinical utility of its implementation in low-income high drug-resistant TB burden countries. To optimise simultaneous detection of resistance within "one test approach" instead of using three different modules - the company has developed a 96-well assay containing probes to most anti-TB medicines currently used in practice. Moreover, this tool allows automatic interpretation of the results with a specific reader simplifying the process and reducing the workload among lab staff