Streptolysin-induced endoplasmic reticulum stress promotes group A streptococcalin vivobiofilm formation and necrotizing fasciitis

Abstract

Group A Streptococcus (GAS) is a human pathogen that causes infections ranging from mild to fulminant and life-threatening. Biofilms have been implicated in acute GAS soft-tissue infections such as necrotizing fasciitis (NF). However, most in vitro models used to study GAS biofilms have been designed to mimic chronic infections and insufficiently recapitulate in vivo conditions and the hostpathogen interactions that might influence biofilm formation. Here we establish and characterize an in vitro model of GAS biofilm development on mammalian cells that simulates microcolony formation observed in a murine model of human NF. We show that on mammalian cells, GAS forms dense aggregates that display hallmark biofilm characteristics including a three-dimensional architecture and enhanced tolerance to antibiotics. In contrast to abiotic-grown biofilms, host-associated biofilms require the expression of secreted GAS streptolysins O and S (SLO, SLS) resulting in the release of a host-associated biofilm promoting-factor(s). Supernatants from GAS-infected mammalian cells or from cells treated with endoplasmic reticulum (ER) stressors restore biofilm formation to an SLO and SLS null mutant that is otherwise attenuated in biofilm formation on cells, together suggesting a role for streptolysin-induced ER stress in this process. In an in vivo mouse model, the streptolysin-null mutant is attenuated in both microcolony formation and bacterial spread, but pre-treatment of softtissue with an ER-stressor restores the ability of the mutant to form wild type like microcolonies that disseminate throughout the soft tissue. Taken together, we have identified a new role of streptolysindriven ER stress in GAS biofilm formation and NF disease progression. Significance StatementAlthough it is well-accepted that bacterial biofilms are associated with many chronic infections, little is known about the mechanisms by which group A Streptococcus (GAS) biofilms contribute to acute soft tissue-invasive diseases like necrotizing fasciitis (NF). In this study, we establish a physiologically relevant in vitro model to study GAS biofilm formation on mammalian cells and validate our findings in a mouse model that mimics human NF. This study demonstrates a novel role of GAS streptolysin-mediated ER stress in the development and spread of GAS biofilms in acute softnot peer-reviewed) is the author/funder. All rights reserved. No reuse allowed without permission.The copyright holder for this preprint (which was . http://dx.doi.org/10.1101/183012 doi: bioRxiv preprint first posted online Aug. 31, 2017; 3 tissue infections. We also show that biofilm formation depends on the release of a host-associated factor that promotes microcolony formation and GAS dissemination in vivo.

Assessing in vivo and in vitro biofilm development by Streptococcus dysgalactiae subsp. dysgalactiae using a murine model of catheter-associated biofilm and human keratinocyte cell

“…SLS also promotes programmed cell death and enhances inflammation in HEK cells (Flaherty et al, 2015). Studies revealed that SLS promotes host-associated biofilm formation (Vajjala et al, 2019), besides inducing mitochondrial damage and consequently macrophage death (Tsao et al, 2019). Datta and co-works reported that all SLS operon is required for the functional expression of streptolysin S (Datta et al, 2005).…”