The impact of nutritional immunity on Group B streptococcal pathogenesis during wound infection

Abstract

Group B Streptococcus (GBS) is a Gram-positive pathobiont that can cause adverse health outcomes in neonates and vulnerable adult populations. GBS is one of the most frequently isolated bacteria from diabetic (Db) wound infections but is rarely found in the non-diabetic (nDb) wound environment. Previously, RNA sequencing of wound tissue from Db wound infections in lepr d b diabetic mice showed increased expression of neutrophil factors, and genes involved in GBS metal transport such as the zinc (Zn), manganese (Mn), and putative nickel (Ni) import systems. Here, we develop a Streptozotocin-induced diabetic wound model to evaluate the pathogenesis of two invasive strains of GBS, serotypes Ia and V. We observe an increase in metal chelators such as calprotectin (CP) and lipocalin-2 during diabetic wound infections compared to nDb. We find that CP limits GBS survival in wounds of non-diabetic mice but does not impact survival in diabetic wounds. Additionally, we utilize GBS metal transporter mutants and determine that the Zn, Mn, and putative Ni transporters in GBS are dispensable in diabetic wound infection but contributed to bacterial persistence in non-diabetic animals. Collectively, these data suggest that in non-diabetic mice, functional nutritional immunity mediated by CP is effective at mitigating GBS infection, whereas in diabetic mice, the presence of CP is not sufficient to control GBS wound persistence. IMPORTANCE Diabetic wound infections are difficult to treat and often become chronic due to an impaired immune response as well as the presence of bacterial species that establish persistent infections. Group B Streptococcus (GBS) is one of the most frequently isolated bacterial species in diabetic wound infections and, as a result, is one of the leading causes of death from skin and subcutaneous infection. However, GBS is notoriously absent in non-diabetic wounds, and little is known about why this species thrives in diabetic infection. The work herein investigates how alterations in diabetic host immunity may contribute to GBS success during diabetic wound infection.

Virulence characteristics of Gram-positive bacteria isolated from diabetic foot ulcers

“…Due to the high co-incidence of E. faecalis and GBS recovered with S. aureus in diabetic wound tissues, we sought to determine the consequence of polymicrobial infection in vivo . We utilized a murine excision wound model first described by Chong et al for E. faecalis chronic wound infection and induced diabetes in mice via low-dose streptozotocin injections as previously described (Chong et al 2017 , Keogh et al 2022 , Akbari et al 2023 ). Diabetic mice were wounded and infected with either S. aureus (LAC), E. faecalis , (OG1RF) or GBS (A909) alone, or co-infected with S. aureus .…”

“…Male 7–10 week old mice were given low-dose intraperitoneal injections of streptozotocin at 50 mg/kg followed by 250 µl of 25% glucose for five consecutive days as previously described (Akbari et al 2023 ). Mice with glucose levels exceeding 200 mg/dL via glucometer were considered diabetic.…”

“…Mice with glucose levels exceeding 200 mg/dL via glucometer were considered diabetic. Following, we utilized a murine model of chronic wound infection developed by Chong et al (Chong et al 2017 ) that we adapted for GBS infection (Keogh et al 2022 , Akbari et al 2023 ). Briefly, mice were anesthetized with 3% isofluorane and the dorsal area was shaved before treatment with Nair to completely remove hair.…”

An opportunistic pathogen under stress: how Group B Streptococcus responds to cytotoxic reactive species and conditions of metal ion imbalance to survive

“…For example, a functional Zn import system is required for iGBS disease in a mouse model (Burcham et al 2020 ); Mn import supports GBS survival in the FRT, and GBS lacking systems that maintain homeostasis of metals such as Zn, Cu, Nickel (Ni), magnesium, and Mn are attenuated for colonization of the FRT (Burcham et al 2022 ). Functional intracellular metal homeostasis is also required for GBS persistence in a murine model of nondiabetic wound infection, with Mn and Zn uptake systems playing an important role in GBS survival within that niche (Akbari et al 2023 ). GBS also require Mn uptake to survive in human whole blood and plasma, and at low pH (Shabayek et al 2016 , Zhu et al 2020 ).…”

Current research update on group B streptococcal infection related to obstetrics and gynecology

“…Several clinical diseases have been confirmed to be caused by GBS infection. The most common diseases are skin and soft tissue infections ( Akbari et al, 2023 ), and GBS can also cause vaginal infections in non-pregnant women. This infection can cause symptoms such as vaginal inflammation ( Tano et al, 2021 ), abnormal vaginal discharge ( Dilrukshi et al, 2021 ), and itching ( Tano et al, 2021 ).…”