Transcriptomic profiling of Streptococcus pyogenes M1T1 strain in a mouse model of necrotizing fasciitis
Authors: Hirose Yujiro , Yamaguchi Masaya , Okuzaki Daisuke , Motooka Daisuke , Hamamoto Hiroshi , Hanada Tomoki , Sumitomo Tomoko , Nakata Masanobu , Kawabata Shigetada 
Published: April 2019

Streptococcus pyogenes is a major cause of necrotizing fasciitis, a life-threatening subcutaneous soft-tissue infection. At the host infection site, the local environment and interaction between host and bacteria affect bacterial gene-expression profiles, but the S. pyogenes gene-expression pattern in necrotizing fasciitis remains unknown. In this study, we used a mouse model of necrotizing fasciitis and performed RNA-sequencing (RNA-seq) analysis of S. pyogenes M1T1 strain 5448 by using infected hindlimbs obtained at 24, 48, and 96 h post-infection. The RNA-seq analysis identified 483 bacterial genes whose expression was consistently altered in the infected hindlimbs as compared to their expression under in vitro conditions. The consistently enriched genes during infection included 306 genes encoding molecules involved in virulence, carbohydrate utilization, amino acid metabolism, trace-metal transport and vacuolar ATPase transport system. Surprisingly, drastic upregulation of 3 genes, encoding streptolysin S precursor (sagA), cysteine protease (speB), and secreted DNase (spd), was noted in the mouse model of necrotizing fasciitis (log2 fold-change values: >6.0, >9.4, and >7.1, respectively). Conversely, the consistently downregulated genes included 177 genes, containing genes associated with oxidative-stress response and cell division. These results suggest that S. pyogenes in necrotizing fasciitis changes its metabolism, decreases cell proliferation, and upregulates the expression of major toxins. Our findings could provide critical information for developing novel treatment strategies and vaccines for necrotizing fasciitis.

Author summary

Necrotizing fasciitis, a life-threatening subcutaneous soft-tissue infection, principally caused by a Streptococcus pyogenes. At infection sites in hosts, bacterial pathogens are exposed to drastically changing environmental conditions and alter global gene expression patterns for survival and pathogenesis. However, there is no previous report about transcriptomic profiling of S. pyogenes in the necrotizing fasciitis. Here, we conducted comprehensive gene-expression analyses of S. pyogenes in the mouse model of necrotizing fasciitis at three distinct time points during infection. Our results indicated that S. pyogenes drastically upregulates the expression of virulence-associated genes and shifts metabolic-pathway usage during infection. The high-level expressions in particular of toxins, such as cytolysins, proteases, and nucleases, were observed at infection sites. In addition, the consistently enriched genes identified here included genes for metabolism of arginine and histidine, and carbohydrate uptake and utilization. Conversely, the genes associated with oxidative-stress response and cell division were consistently downregulated in the mouse model of necrotizing fasciitis. These data will provide useful information necessary for establishing novel treatment strategies (166 words).