Intrapartum antibiotic prophylaxis selects for mutators in group B streptococci among persistently colonized patients

Through vaginal colonization, GBS causes severe pregnancy outcomes including neonatal sepsis and meningitis. Although intrapartum antibiotic prophylaxis (IAP) has reduced early-onset disease rates, persistent GBS colonization has been observed in patients following prophylaxis. To determine whether IAP selects for genomic signatures that enhance GBS survival and persistence in the vaginal tract, whole-genome sequencing was performed on 97 isolates from 58 patients before (prenatal) and after (postpartum) IAP/childbirth. Core-gene mutation analysis identified 7,025 mutations between the paired isolates. Three postpartum isolates accounted for 98% of mutations and were classified as "mutators" because of point mutations within DNA repair systems. In vitro assays revealed stronger biofilms in two mutators. These findings suggest that antibiotics select for mutations that promote survival in vivo, which increases the likelihood of transmission to neonates. They also demonstrate how mutators can provide a reservoir of beneficial mutations that enhance fitness and genetic diversity in the GBS population.

Production and Composition of Group B Streptococcal Membrane Vesicles Vary Across Diverse Lineages

Although the neonatal and fetal pathogen Group B Streptococcus (GBS) asymptomatically colonizes the vaginal tract of ∼30% of pregnant women, only a fraction of their offspring develops invasive disease. We and others have postulated that these dimorphic clinical phenotypes are driven by strain variability; however, the bacterial factors that promote these divergent clinical phenotypes remain unclear. It was previously shown that GBS produces membrane vesicles (MVs) that contain active virulence factors capable of inducing adverse pregnancy outcomes. Because the relationship between strain variation and vesicle composition or production is unknown, we sought to quantify MV production and examine the protein composition, using label-free proteomics on MVs produced by diverse clinical GBS strains representing three phylogenetically distinct lineages. We found that MV production varied across strains, with certain strains displaying nearly twofold increases in production relative to others. Hierarchical clustering and principal component analysis of the proteomes revealed that MV composition is lineage-dependent but independent of clinical phenotype. Multiple proteins that contribute to virulence or immunomodulation, including hyaluronidase, C5a peptidase, and sialidases, were differentially abundant in MVs, and were partially responsible for this divergence. Together, these data indicate that production and composition of GBS MVs vary in a strain-dependent manner, suggesting that MVs have lineage-specific functions relating to virulence. Such differences may contribute to variation in clinical phenotypes observed among individuals infected with GBS strains representing distinct lineages.

Localization of insulin degradation products to an intracellular site in isolated rat hepatocytes

In the present study, we have examined whether insulin degradation products are present on the surface of isolated rat hepatocytes and can be removed by an acid dissociation technique. Hepatocytes were incubated with [125I]insulin for 30 minutes, rapidly washed to remove unbound insulin, and then briefly exposed to acidic conditions (pH 5.0) to remove bound hormone from the cell surface. The radioactive material removed from the cell by acid dissociation and that remaining with the cells were separately analyzed by high performance liquid chromatography. The two primary degradation products of insulin present in control cell extracts were found only with the cell-associated material after acid dissociation. The insulin-sized radioactive material in the extract of acid-dissociable material consisted of only intact [125I]insulin. These results show that the two primary degradation products of insulin in rat hepatocytes are found only intracellularly and suggest that the degradation of the hormone begins after it is internalized.