A streptococcal lipid toxin induces membrane permeabilization and pyroptosis leading to fetal injury.
Bottom Line: Here, we show that the GBS pigment induces membrane permeability in artificial lipid bilayers and host cells.Macrophages lacking the NLRP3 inflammasome recovered from pigment-induced cell damage.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.
Affiliation: Department of Pediatric Infectious Diseases, University of Washington and Seattle Children's Research Institute, Seattle, WA, USA Department of Global Health, University of Washington, Seattle, WA, USA.Show MeSH
Related in: MedlinePlus
Mentions: Previous work from our group demonstrated that hyperhemolytic GBS strains with mutations in CovR/S were more proficient in penetration of human placenta and were also isolated from chorioamniotic membranes and amniotic fluid from women in preterm labor (Whidbey et al, 2013). To determine if hyperhemolytic GBS strains induce fetal injury and preterm birth, we adapted a murine model of E. coli-induced in utero infection (Elovitz et al, 2003) to GBS. We chose the intrauterine model of inoculation rather than a vaginal model of inoculation to minimize discrepancies that can be attributed to differences in mouse vaginal persistence (Patras et al, 2013). To this end, on day E14.5 of pregnancy, either WT GBS, the hyperpigmented ΔcovR, or the non-hemolytic ΔcovRΔcylE was infused into the right horn of the uterus between the first (P1) and second (P2) fetal sacs most proximal to the cervix as described (Hirsch et al, 1995; Elovitz et al, 2003) (also see Fig7A). Mice were monitored for 72 h for signs of preterm birth (i.e., at least 1 pup in cage). At either 72 h or at the onset of delivery (whichever occurred first), fetal survival rates were determined and tissue was collected to assess bacterial load. Preterm birth (i.e., at least 1 pup in cage) was observed in three of six mice infected with ΔcovR, in one of six infected with WT GBS, and in none of the six mice infected with the non-hemolytic ΔcovRΔcylE strain (preterm delivery rates were 50, 16, and 0%, respectively). We also observed significantly higher fetal death in mice infected with hemolytic GBS, that is, WT or hyperpigmented ΔcovR compared to the non-hemolytic ΔcovRΔcylE strain (Fig7B). Bacteria were recovered from all fetuses present in the uterus, and there was no significant difference in bacterial load between fetuses of mice infected with the three GBS strains (data not shown). H&E staining of infected uterine tissue showed that while only a few mononuclear cells are present in the ΔcovRΔcylE sample, increased presence of inflammatory cells and necrotic debris is seen in the ΔcovR sample (Fig7C). The frequency of fetal death between hemolytic strains of GBS such as WT and ΔcovR was not significantly different and may likely be due to decreased repression of hemolysin/pigment biosynthetic genes by CovR/S in utero as suggested previously (Santi et al, 2009; Sitkiewicz et al, 2009).
Affiliation: Department of Pediatric Infectious Diseases, University of Washington and Seattle Children's Research Institute, Seattle, WA, USA Department of Global Health, University of Washington, Seattle, WA, USA.