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WGS-based genetic diversity assessment of LAM genotype M. tuberculosis strains among the tuberculosis outbreaks in distant Latvian counties

D Sadovska(1,2) I Pole(1,3) I Ozere(2,3) A Viksna(2,3) I Norvaisa(3) R Ranka(1,2)

1: Latvian Biomedical Research and Study Centre, Riga, Latvia; 2:Riga Stradins University, Riga, Latvia; 3:Riga East Clinical University Hospital, Centre of Tuberculosis and Lung Diseases, Stopini region, Upeslejas, Latvia

Mycobacterium tuberculosis (Mtb) strains of the Latin American-Mediterranean (LAM) genotype family commonly cause cavitary tuberculosis (TB) and are associated with higher bacillary load. Although this genotype is widespread in Latvia, a little is known about its local genetic diversity. Herein, we delineated the transmission network of six local TB outbreaks caused by LAM Mtb strains that occurred in six distinct Latvian counties and assessed the genetic distances between Mtb isolates. WGS was performed on Mtb isolates obtained from epidemiological clusters of 13 (A), 12 (B), five (CDE), and three (F) patients diagnosed in 2004-2019; four patients had a recurrent episode. Isolates of four outbreaks (BCDE) belonged to the SIT254 spoligotype, while isolates of A and F outbreaks had SIT42 corresponding pattern. The maximum genetic distance between SIT254 Mtb isolates was 99 SNVs, while between SIT42 isolates it reached 112 SNVs. Within the clusters, all but one Mtb isolates exhibited pairwise distances of 0-11 SNVs. Notably, Mtb isolates of three geographically distinct epidemiological clusters formed a bigger outbreak with maximum distance of 16 SNVs between isolates. To conclude, results demonstrated genetic relatedness between all studied isolates belonging to two LAM family spoligotypes and highlighted a possible Mtb strain transmission between distant Latvian counties. This study was supported by ERDF grant No.

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