BackgroundThe interaction between different drug-resistant mutations is important to the development of drug resistance and its evolution. In this study, we aimed to reveal the potential relationships between mutations conferring resistance to two important antituberculosis drugs streptomycin (STR) and fluoroquinolones (FLQ).Materials and methodsWe used an in vitro competitive fitness assay to reveal the interactions between different mutations of rpsL and gyrA in drug-resistant Mycobacterium smegmatis, followed by the analysis of the frequency of rpsL and gyrA mutation combinations in 213 STR–FLQ dual-resistant clinical Mycobacterium tuberculosis isolates from Sichuan region, which was also investigated by the whole genome data from 3,056 global clinical M. tuberculosis isolates.ResultsThe strains with K43R and K88R mutation in rpsL showed no difference in relative fitness compared with their susceptible ancestor, while K43N, K43M, K43T, and K88E exhibited a significantly lower relative fitness (P<0.05). For the FLQ-resistant mutants, all mutation types showed no difference in their relative fitness. Among STR–FLQ dual-resistant M. smegmatis strains, a lower fitness was detected in those with K43N/M/T and K88E instead of K43R and K88R mutations in rpsL. Among M. tuberculosis isolates harboring rpsL and gyrA dual mutations, the most two frequent combinatorial mutation types were K43R/D94G (n=37) and K43R/A90V (n=24), with the former being the most frequent one by both in vitro tests and clinical survey.ConclusionOur results suggest that the interaction between rpsL and gyrA mutations affects the fitness cost in STR–FLQ dual-resistant M. smegmatis and also the predilection of mutation combinations in clinical M. tuberculosis isolates.

Background Lineage 4 of Mycobacterium tuberculosis complex (MTBC), mainly epidemic in Europe and Americas, presents in high proportions in South China and is believed to enter China around the 13th century, when the important human migratory events of the Maritime Silk Road and “Huguang Filling Sichuan” population migration happened in China. This study was to explain the coincidence of these two events with lineage 4’s high proportion in South China. Methods Based on the spatial interpolation analysis of the genotyping data of 25,575 MTBC isolates, the distribution of lineage 4 was compared with that of targeted surname populations and the Maritime Silk Road’s main ports. Results The results showed that lineage 4 distribution in China could be mapped to the regions affected by “Huguang Filling Sichuan” population migration; while the distribution of lineage 4’s two sub-lineages in Asia, Europe, Africa and Oceania could be best explained by the Maritime Silk Road. Conclusion Our results suggest that these two events might pose a crucial shared influence, leading to the greater incidence of lineage 4 in South China. And this may contribute to our better understanding of the prevailing tuberculosis landscape in China and facilitate the epidemiological investigations and tracking of emerging MTBC clones.

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Background: Beijing sub-pedigree 2 (BSP2) and T sub-lineage 6 (TSL6) are two clades belonging to Beijing and T family of Mycobacterium tuberculosis (MTB), respectively, defined by Bayesian population structure analysis based on 24-loci mycobacterial interspersed repetitive unit-variable number of tandem repeats (MIRU-VNTR). Globally, over 99% of BSP2 and 89% of TSL6 isolates were distributed in Chongqing, suggesting their possible local adaptive evolution. The objective of this paper is to explore whether BSP2 and TSL6 originated by their local adaptive evolution from the specific isolates of Beijing and T families in Chongqing. Methods: The genotyping data of 16 090 MTB isolates were collected from laboratory collection, published literatures and SITVIT database before subjected to Bayesian population structure analysis based on 24-loci MIRU-VNTR. Spacer Oligonucleotide Forest (Spoligoforest) and 24-loci MIRU-VNTR-based minimum spanning tree (MST) were used to explore their phylogenetic pathways, with Bayesian demographic analysis for exploring the recent demographic change of TSL6. Results: Phylogenetic analysis suggested that BSP2 and TSL6 in Chongqing may evolve from BSP4 and TSL5, respectively, which were locally predominant in Tibet and Jiangsu, respectively. Spoligoforest showed that Beijing and T families were genetically distant, while the convergence of the MIRU-VNTR pattern of BSP2 and TSL6 was revealed by WebLogo. The demographic analysis concluded that the recent demographic change of TSL6 might take 111.25 years.