Non-tuberculous mycobacteria hybridisation profiles in the GenoType MTBDRplus assay: experience from a diagnostic routine of a high-throughput laboratory

Abstract

Introduction. Disease caused by non-tuberculous mycobacteria (NTM) is an emergent problem. Because NTM pulmonary disease and tuberculosis (TB) have similar clinical presentations, many cases of NTM may be misdiagnosed as TB before laboratory identification of the NTM species. Hypothesis/Gap Statement. Clinical laboratories should always perform differentiation between Mycobacterium tuberculosis complex (MTBC) and NTM to guide patients' correct treatment. Aim. To describe the characteristics and to identify mycobacterial isolates presumptively classified as MTBC by macroscopic characteristics in culture media that tested negative in GenoType MTBDRplus. Methodology. All cultures from February 2019 to December 2021 showing MTBC macroscopic characteristics were processed by GenoType MTBDRplus. MTBC-negative cultures underwent species identification by immunochromatography, line probe assays and PRA-hsp65. Patients’ data were obtained from Brazilian surveillance systems. Results. Only 479 (3.1%) of 15 696 isolates presumptively identified as MTBC were not confirmed by GenoType MTBDRplus and were then subjected to identification. A total of 344 isolates were shown to be NTM, of which 309 (64.5%) and 35 (7.3%) were identified to the species and genus levels, respectively. Of the 204 NTM isolates with MTBC characteristics, the most frequent species were M. fortuitum (n=52, 25.5%), M. abscessus complex (MABC; n=27, 13.2%) and M. avium complex (MAC; n=26, 12.7%). Regarding the GenoType MTBDRplus results from NTM isolates, there were diverse hybridisation profiles with rpoB gene’s different wild-type (WT) probes. Seventy-six (16.1%) of the 473 patients were classified as having NTM disease, the most frequent being MAC (n=15, 19.7%), MABC (n=13, 17.1%), M. kansasii (n=10, 13.2%) and M. fortuitum (n=6, 7.9%). Conclusion. Because the signs and symptoms of pulmonary TB are similar to those of pulmonary mycobacteriosis and treatment regimens for TB and NTM are different, identifying the disease-causing species is paramount to indicate the correct management. Thus, in the laboratory routine, when an isolate presumptively classified as MTBC is MTBC-negative, it is still essential to perform subsequent identification.