Whole genome sequencing of Bulgarian rifampicin resistant strains.

Introduction: The transmission of drug-resistant tuberculosis is one of the greatest challenges facing the global tuberculosis control.

Aim: The aim of the study was to investigate the resent transmission of rifampicin resistant tuberculosis in Bulgaria and to describe the mutations related to the antimicrobials' resistance using whole genome sequencing.

Materials And Methods: As part of an ECDC funded pilot study for evaluation of the systematic use of whole genome sequencing (WGS) of Mycobacterium tuberculosis (MTB) surveillance (EUSeqMyTB), Bulgaria provided 65 rifampicin resistant isolates over a three years' timeframe (2017-2019) representing 87.5% of the notified rifampicin resistant cases. Drug resistance prediction and relatedness analysis of the resistant isolates was performed in collaboration with San Raffaele Scientific Institute, Milan, Italy.

Results: Almost all of the isolates were identified as Euro-American lineage (96.9%); 18.5% of the isolates were found to be resistant to fluoroquinolones, but no mutations conferring resistance to bedaquiline or linezolid could be identified. Less than half (43.3%) of the isolates were clustered (<5 SNPs distance) into a total of seven national SNP-based clusters, while a total of six isolates were found to be part of different cross-border clusters. All clustered cases originated from Bulgaria.

Conclusions: WGS has proven to be a reliable tool for surveillance and tracing of recent transmission of tuberculosis and has the potential for resistance prediction for most of the antituberculosis drugs.