Immunization With a Secreted Esterase Protects Mice Against Multiple Serotypes (M1, M3, and M28) of Group A Streptococcus

Functional and Transcriptome Analysis of Streptococcus pyogenes Virulence on Loss of Its Secreted Esterase

Esterases are broadly expressed in bacteria, but much remains unknown about their pathogenic effect. In previous studies, we focused on an esterase secreted by Streptococcus pyogenes (group A Streptococcus, GAS). Streptococcal secreted esterase (Sse) can hydrolyze the sn−2 ester bonds of platelet−activating factor (PAF), converting it to an inactive form that inhibits neutrophil chemotaxis to the infection sites. However, as a virulent protein, Sse probably participates in GAS pathogenesis far beyond chemotaxis inhibition. In this study, we generated the sse gene knockout strain (Δsse) from the parent strain MGAS5005 (hypervirulent M1T1 serotype) and compared the difference in phenotypes. Absence of Sse was related to weakened skin invasion in a murine infection model, and significantly reduced GAS epithelial adherence, invasion, and intracellular survival. Reduced virulence of the Δsse mutant strain was explored through transcriptome analysis, revealing a striking reduction in the abundance of invasive virulence factors including M protein, SIC, ScpA, and SclA. Besides the influence on the virulence, Sse also affected carbohydrate, amino acid, pyrimidine, and purine metabolism pathways. By elucidating Sse−mediated pathogenic process, the study will contribute to the development of new therapeutic agents that target bacterial esterases to control clinical GAS infections.

Attenuation of virulence in multiple serotypes (M1, M3, and M28) of Group A Streptococcus after the loss of secreted esterase

INTRODUCTION

Group A Streptococcus (GAS) can produce streptococcal secreted esterase (Sse), which inhibits neutrophil recruitment to the site of infection and is crucial for GAS pathogenesis. As an effective esterase, Sse hydrolyzes the sn-2 ester bond of human platelet-activating factor, inactivating it and abolishing its ability to recruit neutrophils.

OBJECTIVES

The purpose of this study was to investigate the effects of sse deletion on the virulence of multiple serotypes of GAS.

METHODS

Isogenic strains that lack the sse gene (Δsse) were derived from the parent strains MGAS5005 (serotype M1, CovRS mutant), MGAS2221 (serotype M1, wild-type CovRS), MGAS315 (serotype M3, CovRS mutant) and MGAS6180 (serotype M28, wild-type CovRS) and were used to study the differences in virulence and pathogenicity of GAS serotypes.

RESULTS

In a subcutaneous infection model, mice infected with MGAS5005^Δsse exhibited higher survival rates but decreased dissemination to the organs compared with mice infected with MGAS5005. When mice were infected with the four Δsse mutants, the MPO activity and IFN-γ, TNF-α, IL-2 and IL-6 levels increased, but the skin lesion sizes decreased. In an intraperitoneal infection model, the absence of Sse significantly reduced the virulence of GAS, leading to increased mouse survival rates and decreased GAS burdens in the organs in most of the challenge experiments. In addition, the numbers of the four Δsse mutants were greatly reduced 60 min after incubation with isolated rat neutrophils.

CONCLUSION

Our results suggest that Sse participates in the pathogenesis of multiple GAS serotypes (MGAS5005, MGAS2221, MGAS315 and MGAS6180), particularly the hypervirulent CovS mutant strains MGAS5005 and MGAS315. These strain differences were positively correlated with the virulence of the serotype.