Kelvin Kian Long Chong
Profile Url: kelvin-kian-long-chong
Researcher at Interdisciplinary Graduate School, Nanyang Technological University
0
0
0
Video Abstract (AI generated)
Paper
Preprint
Group A Streptococcus (GAS) is a human pathogen that causes infections ranging from mild to fulminant and life-threatening. Biofilms have been implicated in acute GAS soft-tissue infections such as necrotizing fasciitis (NF). However, most in vitro models used to study GAS biofilms have been designed to mimic chronic infections and insufficiently recapitulate in vivo conditions and the host-pathogen interactions that might influence biofilm formation. Here we establish and characterize an in vitro model of GAS biofilm development on mammalian cells that simulates microcolony formation observed in a murine model of human NF. We show that on mammalian cells, GAS forms dense aggregates that display hallmark biofilm characteristics including a three-dimensional architecture and enhanced tolerance to antibiotics. In contrast to abiotic-grown biofilms, host-associated biofilms require the expression of secreted GAS streptolysins O and S (SLO, SLS) resulting in the release of a host-associated biofilm promoting-factor(s). Supernatants from GAS-infected mammalian cells or from cells treated with endoplasmic reticulum (ER) stressors restore biofilm formation to an SLO and SLS null mutant that is otherwise attenuated in biofilm formation on cells, together suggesting a role for streptolysin-induced ER stress in this process. In an in vivo mouse model, the streptolysin-null mutant is attenuated in both microcolony formation and bacterial spread, but pre-treatment of soft-tissue with an ER-stressor restores the ability of the mutant to form wild type like microcolonies that disseminate throughout the soft tissue. Taken together, we have identified a new role of streptolysin-driven ER stress in GAS biofilm formation and NF disease progression.
0
0
0
Infection and Immunity, 2017-09-11
Video Abstract (AI generated)
Paper
Preprint
Infection and Immunity
Enterococcus faecalis is a member of the human gastrointestinal microbiota and is an opportunistic pathogen associated with hospital-acquired infections (HAIs) of wounds, the bloodstream, and the urinary tract. E. faecalis has the ability to subvert or evade immune-mediated clearance, although the mechanisms underlying this are poorly understood. In this study, we examine the ability of E. faecalis to subvert macrophage activation. We show that E. faecalis actively prevents NF-κB driven signaling in mouse RAW264.7 macrophages both in the presence of Toll-like receptor agonists and during polymicrobial infection with Escherichia coli. Co-infection with E. faecalis and E. coli in a mouse model of catheter-associated urinary tract infection (CAUTI) results in a reduced macrophage transcriptional response in the bladder compared to E. coli infection alone. Finally, we demonstrate that co-inoculation of E. faecalis with E. coli into the catheterized bladder significantly augments E. coli CAUTI. Taken together, these results implicate E. faecalis suppression of NF-κB-driven responses in macrophages with polymicrobial CAUTI pathogenesis.
0
0
0
The Journal of Infectious Diseases, 2017-10-17
Video Abstract (AI generated)
Paper
Preprint
The Journal of Infectious Diseases
Enterococcus faecalis is one of most frequently isolated bacterial species in wounds yet little is known about its pathogenic mechanisms in this setting. Here, we used a mouse wound excisional model to characterize the infection dynamics of E. faecalis and show that infected wounds result in two different states depending on the initial inoculum. Low dose inocula were associated with short term, low titer colonization whereas high dose inocula were associated with acute bacterial replication and long term persistence. High dose infection and persistence were also associated with immune cell infiltration, despite suppression of some inflammatory cytokines and delayed wound healing. During high dose infection, the multiple peptide resistance factor (MprF) which is involved in resisting immune clearance, contributes to E. faecalis fitness. These results comprehensively describe a mouse model for investigating E. faecalis wound infection determinants, and suggest that both immune modulation and resistance contribute to persistent, non-healing wounds.
0
0
0
Video Abstract (AI generated)
Paper
Preprint
Enterococcus faecalis is an opportunistic human pathogen and the cause of biofilm-associated infections of the heart, catheterized urinary tract, wounds, and the dysbiotic gut where it can expand to high numbers upon microbiome perturbations. The E. faecalis sortase-assembled endocarditis and biofilm associated pilus (Ebp) is involved in adhesion and biofilm formation in vitro and in vivo. Extracellular electron transfer (EET) also promotes E. faecalis biofilm formation in iron-rich environments, however neither the mechanism underlying EET nor its role in virulence was previously known. Here we show that iron associated with Ebp serve as a terminal electron acceptor for EET, leading to extracellular iron reduction and intracellular iron accumulation. We found that a MIDAS motif within the EbpA tip adhesin is required for interaction with iron, EET, and FeoB-mediated iron uptake. We demonstrate that MenB and Ndh3, essential components of the aerobic respiratory chain and a specialized flavin-mediated electron transport chain, respectively, are required for iron-mediated EET. In addition, using a mouse gastrointestinal (GI) colonization model, we show that EET is essential for colonization of the GI tract, and Ebp is essential for augmented E. faecalis GI colonization when dietary iron is in excess. Taken together, our findings show that pilus mediated capture of iron within biofilms enables EET-mediated iron acquisition in E. faecalis, and that these processes plays an important role in E. faecalis expansion in the GI tract.
0
0
0
Infection and Immunity, 2020-03-30
Video Abstract (AI generated)
Paper
Preprint
Infection and Immunity
Bacterial pathogens encounter a variety of nutritional environments in the human host, including nutrient metal restriction and overload. Uptake of manganese (Mn) is essential for Enterococcus faecalis growth and virulence; however, it is not known how this organism prevents Mn toxicity. In this study, we examine the role of the highly conserved MntE transporter in E. faecalis Mn homeostasis and virulence. We show that inactivation of mntE results in growth restriction in presence of excess Mn, but not other metals, demonstrating its specific role in Mn detoxification. Upon growth in the presence of excess Mn, an mntE mutant accumulates intracellular Mn, iron (Fe), and magnesium (Mg), supporting a role for MntE in Mn and Fe export, and a role for Mg in offsetting Mn toxicity. Growth of the mntE mutant in excess Fe also results in increased levels of intracellular Fe, but not Mn or Mg, providing further support for MntE in Fe efflux. Inactivation of mntE in the presence of excess iron also results in the upregulation of glycerol catabolic genes and enhanced biofilm growth, and addition of glycerol is sufficient to augment biofilm growth for both the mntE mutant and its wild type parental strain, demonstrating that glycerol availability significantly enhances biofilm formation. Finally, we show that mntE contributes to infection of the antibiotic-treated mouse gastrointestinal (GI) tract, suggesting that E. faecalis encounters excess Mn in this niche. Collectively, these findings demonstrate that the manganese exporter MntE plays a crucial role in E. faecalis metal homeostasis and virulence.