A streptococcal lipid toxin induces membrane permeabilization and pyroptosis leading to fetal injury.

Joseph A Duncan,Kristina M Adams Waldorf,Christopher Whidbey,Jay Vornhagen,Erica Boldenow,Michal A Elovitz,Ejiofor A D Ezekwe,Kenji Doering,Denny Liggitt,Lisa Ngo,Jens H Gundlach,Claire Gendrin,Lakshmi Rajagopal,Jenny Mae Samson

doi:10.15252/emmm.201404883

Abstract

Group B streptococci (GBS) are Gram-positive bacteria that cause infections in utero and in newborns. We recently showed that the GBS pigment is hemolytic and increased pigment production promotes bacterial penetration of human placenta. However, mechanisms utilized by the hemolytic pigment to induce host cell lysis and the consequence on fetal injury are not known. Here, we show that the GBS pigment induces membrane permeability in artificial lipid bilayers and host cells. Membrane defects induced by the GBS pigment trigger K+ efflux leading to osmotic lysis of red blood cells or pyroptosis in human macrophages. Macrophages lacking the NLRP3 inflammasome recovered from pigment-induced cell damage. In a murine model of in utero infection, hyperpigmented GBS strains induced fetal injury in both an NLRP3 inflammasome-dependent and NLRP3 inflammasome-independent manner. These results demonstrate that the dual mechanism of action of the bacterial pigment/lipid toxin leading to hemolysis or pyroptosis exacerbates fetal injury and suggest that preventing both activities of the hemolytic lipid is likely critical to reduce GBS fetal injury and preterm birth.

Highlights

Group B streptococci (GBS) are Gram-positive bacteria that cause infections in utero and in newborns
To determine if membrane permeability observed with the GBS pigment requires the active cellular response of host cells, we tested the ability of the pigment to disrupt artificial lipid bilayers using model black lipid membranes (BLMs)
Fetal death was significantly higher in NLRP3 knockout (NLRP3KO) mice infected with DcovR compared to NLRP3KO mice infected with DcovRDcylE; these results indicate that the hemolytic/membrane-disrupting nature of the pigment is likely to contribute to fetal injury

Summary

Introduction

Group B streptococci (GBS) are Gram-positive bacteria that cause infections in utero and in newborns. Mechanisms utilized by the hemolytic pigment to induce host cell lysis and the consequence on fetal injury are not known. Membrane defects induced by the GBS pigment trigger K+ efflux leading to osmotic lysis of red blood cells or pyroptosis in human macrophages. In a murine model of in utero infection, hyperpigmented GBS strains induced fetal injury in both an NLRP3 inflammasome-dependent and NLRP3 inflammasome-independent manner. These results demonstrate that the dual mechanism of action of the bacterial pigment/ lipid toxin leading to hemolysis or pyroptosis exacerbates fetal injury and suggest that preventing both activities of the hemolytic lipid is likely critical to reduce GBS fetal injury and preterm birth

Objectives

Results

Conclusion