Group B Streptococcus (GBS) asymptomatically colonizes the female reproductive tract but is a common causative agent of meningitis. GBS meningitis is characterized by extensive infiltration of neutrophils carrying high concentrations of calprotectin, a metal chelator. To persist within inflammatory sites and cause invasive disease, GBS must circumvent host starvation attempts. Here, we identified global requirements for GBS survival during calprotectin challenge, including known and putative systems involved in metal ion transport. We characterized the role of zinc import in tolerating calprotectin stress in vitro and in a mouse model of infection. We observed that a global zinc uptake mutant was less virulent than the parental GBS strain and found calprotectin knockout mice to be equally susceptible to infection by wild-type (WT) and mutant strains. These findings suggest that calprotectin production at the site of infection results in a zinc-limited environment and reveals the importance of GBS metal homeostasis to invasive disease.

The vaginal tract is a complex environment that changes throughout various life stages. Recent advances have improved our understanding of the vaginal microbiota and the influence of host factors on microbial colonization. The vaginal niche is characterized by unique qualities such as high abundances of glycogen and mucin, low pH, active cellular immunity, and fluctuations in hormone signaling that support a complex microbiota. While traditionally thought to be dominated by Lactobacillus species, emerging research highlights a more diverse microbiota, including both commensal and potentially pathogenic microbes. Given the interconnectedness of the microbial and host factors in this environment, minor shifts can lead to significant downstream effects on health. This review takes an ecosystems approach to explore the multifaceted relationship between the vaginal mucosa, the microbiota, and influences of environmental factors on shaping the two. We discuss the contribution of hormone signaling in shaping microbial communities, concepts of vaginal community stability and dysbiosis, and the emerging understanding of microbial metabolism and cross-feeding dynamics within the vaginal tract. Additionally, we will examine the interactions between microbes and immune cells in the vaginal mucosa, including mechanisms by which the immune system modulates the local environment. By considering the feedback loops between the host and the resident microbiota, we propose key knowledge gaps and suggest interdisciplinary avenues for future research aimed at improving our understanding of vaginal health and disease. Understanding these complex interactions is important for advancing vaginal healthcare across all individuals.

Streptococcus spp. are an important genus of Gram-positive bacteria, many of which are opportunistic pathogens that are capable of causing invasive disease in a wide range of populations. Metals, especially transition metal ions, are an essential nutrient for all organisms. Therefore, to survive across dynamic host environments, Streptococci have evolved complex systems to withstand metal stress and maintain metal homeostasis, especially during colonization and infection. There are many different types of transport systems that are used by bacteria to import or export metals that can be highly specific or promiscuous. Focusing on the most well studied transition metals of zinc, manganese, iron, nickel, and copper, this review aims to summarize the current knowledge of metal homeostasis in pathogenic Streptococci, and their role in virulence.

Streptococcus pneumoniae colonizes the human nasopharyngeal mucosa and is a leading cause of community-acquired pneumonia, acute otitis media, and bacterial meningitis. Metal ion homeostasis is vital to the survival of this pathogen across diverse biological sites and contributes significantly to colonization and invasive disease. Microarray and qRT-PCR analysis revealed an upregulation of an uncharacterized operon (SP1433-1438) in pneumococci subjected to metal-chelation by N,N,N′,N′-tetrakis-(2-pyridylmethyl)ethylenediamine (TPEN). Supplementation of zinc, cobalt, and nickel following TPEN treatment significantly abrogated induction. BLASTP comparisons and protein topology analysis predicted this locus to encode components of ATP binding cassette (ABC) transporters involved in multidrug resistance (SP1434-1435) and energy-coupling factor (ECF) transporters (SP1436-1438). Inductively coupled plasma mass spectrometry (ICP-MS) analysis identified differences in intracellular metal content in a Δ1434-8 mutant strain compared to parental T4R. Further, analysis of the secreted metabolome of WT and Δ1434-8 strains identified significant changes in pneumococcal glycolytic and amino acid metabolic pathways, indicating a shift towards mixed acid fermentation. Additionally, proteomic analysis revealed differentially expressed proteins in the Δ1434-8 mutant strain, with nearly 20% regulated by the global catabolite repressor, CcpA. Based on these findings, we propose that the transporters encoded by SP1433-1438 are involved in regulating the central metabolism of S. pneumoniae and contributing to bacterial survival during metal stress.

Streptococcus agalactiae (Group B Streptococcus, GBS) is the leading cause of neonatal sepsis and meningitis but has been recently isolated from non-pregnant adults with underlying medical conditions like diabetes. Despite diabetes being a key risk factor for invasive disease, the pathological consequences during GBS infection remain poorly characterized. Here, we demonstrate the pathogenicity of the GBS90356-ST17 and COH1-ST17 strains in streptozotocin-induced diabetic mice. We show that GBS can spread through the bloodstream and colonize several tissues, presenting a higher bacterial count in diabetic-infected mice when compared to non-diabetic-infected mice. Histological sections of the lungs showed inflammatory cell infiltration, collapsed septa, and red blood cell extravasation in the diabetic-infected group. A significant increase in collagen deposition and elastic fibers were also observed in the lungs. Moreover, the diabetic group presented red blood cells that adhered to the valve wall and disorganized cardiac muscle fibers. An increased expression of KC protein, IL-1β, genes encoding immune cell markers, and ROS (reactive oxygen species) production was observed in diabetic-infected mice, suggesting GBS promotes high levels of inflammation when compared to non-diabetic animals. Our data indicate that efforts to reverse the epidemic of diabetes could considerably reduce the incidence of invasive infection, morbidity and mortality due to GBS.

Murine models are commonly used to understand pathogen and host determinants of systemic infection. While these models have proven beneficial for uncovering bacterial mechanisms required for progression to invasive disease, it can be challenging to draw comparisons across studies as several different routes of infection are standardly used for these experiments. In this study, one of the leading bacterial meningeal pathogens, Streptococcus agalactiae , or Group B Streptococcus (GBS), was used to compare experimental outcomes of two commonly used routes of hematogenous infection, lateral tail vein injection and retro-orbital venous sinus injection. Here we demonstrate that both routes of infection result in systemic disease and the onset of clinical symptoms of infection. We show that retro-orbital venous sinus injection results in an initial increase in bacterial dissemination to the spleen and brain tissue of GBS-infected mice, while an increased bacterial burden was only detected in brain tissues at a later time point. Despite differences in initial dissemination and brain bacterial burden, we found that the route of infection did not significantly impact bacterial burden in the blood, kidney, spleen, heart, and lung tissues at experimental endpoints; and similarly did not impact animal health scores during infection; cytokine and proinflammatory protein abundance in the brain tissue; or overall animal survival. In summary, these findings suggest that both tail vein injection and retro-orbital venous sinus injection are viable models to study Group B streptococcal systemic infection and result in largely similar disease outcomes within our tested parameters. IMPORTANCE: Streptococcus agalactiae or Group B Streptococcus (GBS) is the leading cause of invasive disease in neonates and immunocompromised adults and is implicated in severe cases of sepsis, pneumonia, and meningitis. Established murine models of hematogenous systemic infection allow for better understanding and investigation of bacterial dispersion, pathogenesis, meningeal inflammation, and interaction with the host. Here we compared two routes of infection, intravenous lateral tail vein and retro-orbital venous sinus, demonstrating that similar experimental outcomes can be observed, regardless of the route of infection for GBS, specifically. These findings help to reinforce the utility of different systemic infection models and provide insight into comparisons across different established models and how these models can be applied in microbial research.