A new class of intercellular signal controls toxin production and virulence of human bacterial pathogen Streptococcus pyogenes

Quorum sensing (QS) is a process in which bacteria use diverse signaling molecules to monitor their population density and regulate population-wide expression of genes involved in several key bacterial processes such as virulence, biofilm formation, and antibiotic resistance. Gram-positive bacteria typically use oligopeptides as intercellular signaling molecules. The secreted oligopeptides modulate gene expression by either activating the sensor kinase of a two-component system on the bacterial surface or by interacting with cognate transcription regulator in the bacterial cytosol. The gram-positive bacteria Group A Streptococcus (GAS) is a major human pathogen responsible for over 700 million infections annually worldwide. GAS produces a wide spectrum of virulence factors that play crucial roles in disease pathogenesis. Among the many toxins produced by GAS, Streptococcal pyrogenic exotoxin B (SpeB) is one of the well-studied virulence factor. SpeB is a secreted cysteine protease that is produced abundantly during infection and is critical for GAS pathogenesis. Although SpeB is extensively studied for a century, the precise regulatory events that govern speB gene expression are not fully understood. In this study, we have discovered that GAS employs a previously unknown peptide-mediated quorum sensing pathway to control speB expression during high bacterial population density. GAS genome encodes a novel class of leaderless peptide signal, SpeB-Inducing Peptide (SIP). SIP lacks several characteristic features that are hallmarks of bacterial peptide signals. Contrary to all the characterized bacterial peptide signals, SIP is produced in its mature form and lacks amino acid sequences in the amino terminus required for secretion. Nevertheless, SIP functions as an effective intercellular signal. SIP is secreted and reinternalized into GAS cytosol where it interacts with its cognate regulator, Regulator of proteinase B (RopB). SIP binding to RopB induces allosteric changes in the regulator, which leads to high affinity RopB-DNA interactions, RopB oligomerization and activation of speB gene expression. Importantly, we demonstrate that the SIP signaling pathway is active in vivo and contributes significantly to GAS virulence in multiple mouse models of GAS infection. We also show that the SIP signaling occurs during GAS growth ex vivo in human saliva and blood and SIP-mediated speB expression is crucial for GAS survival in both saliva and blood. Together, our discoveries in this study identify a novel bacterial signaling pathway and suggest new therapeutic strategies for future translation studies

Analysis and synthesis of iris images

Of all the physiological traits of the human body that help in personal identification, the iris is probably the most robust and accurate. Although numerous iris recognition algorithms have been proposed, the underlying processes that define the texture of irises have not been extensively studied. In this thesis, multiple pair-wise pixel interactions have been used to describe the textural content of the iris image thereby resulting in a Markov Random Field (MRF) model for the iris image. This information is expected to be useful for the development of user-specific models for iris images, i.e. the matcher could be tuned to accommodate the characteristics of each user\u27s iris image in order to improve matching performance. We also use MRF modeling to construct synthetic irises based on iris primitive extracted from real iris images. The synthesis procedure is deterministic and avoids the sampling of a probability distribution making it computationally simple. We demonstrate that iris textures in general are significantly different from other irregular textural patterns. Clustering experiments indicate that the synthetic irises generated using the proposed technique are similar in textural content to real iris images

A new class of intercellular signal controls toxin production and virulence of human bacterial pathogen Streptococcus pyogenes

Quorum sensing (QS) is a process in which bacteria use diverse signaling molecules to monitor their population density and regulate population-wide expression of genes involved in several key bacterial processes such as virulence, biofilm formation, and antibiotic resistance. Gram-positive bacteria typically use oligopeptides as intercellular signaling molecules. The secreted oligopeptides modulate gene expression by either activating the sensor kinase of a two-component system on the bacterial surface or by interacting with cognate transcription regulator in the bacterial cytosol. The gram-positive bacteria Group A Streptococcus (GAS) is a major human pathogen responsible for over 700 million infections annually worldwide. GAS produces a wide spectrum of virulence factors that play crucial roles in disease pathogenesis. Among the many toxins produced by GAS, Streptococcal pyrogenic exotoxin B (SpeB) is one of the well-studied virulence factor. SpeB is a secreted cysteine protease that is produced abundantly during infection and is critical for GAS pathogenesis. Although SpeB is extensively studied for a century, the precise regulatory events that govern speB gene expression are not fully understood. In this study, we have discovered that GAS employs a previously unknown peptide-mediated quorum sensing pathway to control speB expression during high bacterial population density. GAS genome encodes a novel class of leaderless peptide signal, SpeB-Inducing Peptide (SIP). SIP lacks several characteristic features that are hallmarks of bacterial peptide signals. Contrary to all the characterized bacterial peptide signals, SIP is produced in its mature form and lacks amino acid sequences in the amino terminus required for secretion. Nevertheless, SIP functions as an effective intercellular signal. SIP is secreted and reinternalized into GAS cytosol where it interacts with its cognate regulator, Regulator of proteinase B (RopB). SIP binding to RopB induces allosteric changes in the regulator, which leads to high affinity RopB-DNA interactions, RopB oligomerization and activation of speB gene expression. Importantly, we demonstrate that the SIP signaling pathway is active in vivo and contributes significantly to GAS virulence in multiple mouse models of GAS infection. We also show that the SIP signaling occurs during GAS growth ex vivo in human saliva and blood and SIP-mediated speB expression is crucial for GAS survival in both saliva and blood. Together, our discoveries in this study identify a novel bacterial signaling pathway and suggest new therapeutic strategies for future translation studies

NETRA: Interactive Display for Estimating Refractive Errors and Focal Range

We introduce an interactive, portable, and inexpensive solution for estimating refractive errors in the human eye. While expensive optical devices for automatic estimation of refractive correction exist, our goal is to greatly simplify the mechanism by putting the human subject in the loop. Our solution is based on a high-resolution programmable display and combines inexpensive optical elements, interactive GUI, and computational reconstruction. The key idea is to interface a lenticular view-dependent display with the human eye in close range - a few millimeters apart. Via this platform, we create a new range of interactivity that is extremely sensitive to parameters of the human eye, like refractive errors, focal range, focusing speed, lens opacity, etc. We propose several simple optical setups, verify their accuracy, precision, and validate them in a user study.Alfred P. Sloan Foundation (Research Fellowship

Modeling Streptococcus pyogenes Pharyngeal Colonization in the Mouse

Streptococcus pyogenes, or Group A Streptococcus (GAS), is a human-restricted pathogen most commonly found in the posterior oropharynx of the human host. The bacterium is responsible for 600 million annual cases of pharyngitis globally and has been found to asymptomatically colonize the pharynxes of 4–30% of the population. As such, many studies have utilized animals as models in order to decipher bacterial and host elements that contribute to the bacterial-pharyngeal interaction and determine differences between acute infection and asymptomatic colonization. The aim of this review is to first describe both bacterial and host factors that are important for the pharyngeal persistence of GAS in humans, then to detail the bacterial and host factors that are important for colonization in murine model, and finally to compare the two in order to evaluate the strength of murine pharyngeal colonization as a model for the human-GAS pharyngeal interaction

The leaderless communication peptide (LCP) class of quorum-sensing peptides is broadly distributed among Firmicutes

Abstract The human pathogen Streptococcus pyogenes secretes a short peptide (leaderless communication peptide, LCP) that mediates intercellular communication and controls bacterial virulence through interaction with its receptor, RopB. Here, we show that LCP and RopB homologues are present in other Firmicutes. We experimentally validate that LCPs with distinct peptide communication codes act as bacterial intercellular signals and regulate gene expression in Streptococcus salivarius, Streptococcus porcinus, Enterococcus malodoratus and Limosilactobacillus reuteri. Our results indicate that LCPs are more widespread than previously thought, and their characterization may uncover new signaling mechanisms and roles in coordinating diverse bacterial traits

A Critical Role of Zinc Importer AdcABC in Group A Streptococcus-Host Interactions During Infection and Its Implications for Vaccine Development

Bacterial pathogens must overcome host immune mechanisms to acquire micronutrients for successful replication and infection. Streptococcus pyogenes, also known as group A streptococcus (GAS), is a human pathogen that causes a variety of clinical manifestations, and disease prevention is hampered by lack of a human GAS vaccine. Herein, we report that the mammalian host recruits calprotectin (CP) to GAS infection sites and retards bacterial growth by zinc limitation. However, a GAS-encoded zinc importer and a nuanced zinc sensor aid bacterial defense against CP-mediated growth inhibition and contribute to GAS virulence. Immunization of mice with the extracellular component of the zinc importer confers protection against systemic GAS challenge. Together, we identified a key early stage host-GAS interaction and translated that knowledge into a novel vaccine strategy against GAS infection. Furthermore, we provided evidence that a similar struggle for zinc may occur during other streptococcal infections, which raises the possibility of a broad-spectrum prophylactic strategy against multiple streptococcal pathogens

Utility of a Machine-Guided Tool for Assessing Risk Behavior Associated With Contracting HIV in Three Sites in South Africa: Protocol for an In-Field Evaluation

BackgroundMobile technology has helped to advance health programs, and studies have shown that an automated risk prediction model can successfully be used to identify patients who exhibit a high probable risk of contracting human immunodeficiency virus (HIV). A machine-guided tool is an algorithm that takes a set of subjective and objective answers from a simple questionnaire and computes an HIV risk assessment score. ObjectiveThe primary objective of this study is to establish that machine learning can be used to develop machine-guided tools and give us a deeper statistical understanding of the correlation between certain behavioral patterns and HIV. MethodsIn total, 200 HIV-negative adult individuals across three South African study sites each (two semirural and one urban) will be recruited. Study processes will include (1) completing a series of questions (demographic, sexual behavior and history, personal, lifestyle, and symptoms) on an application system, unaided (assistance will only be provided upon user request); (2) two HIV tests (one per study visit) being performed by a nurse/counselor according to South African national guidelines (to evaluate the prediction accuracy of the tool); and (3) communicating test results and completing a user experience survey questionnaire. The output metrics for this study will be computed by using the participants’ risk assessment scores as “predictions” and the test results as the “ground truth.” Analyses will be completed after visit 1 and then again after visit 2. All risk assessment scores will be used to calculate the reliability of the machine-guided tool. ResultsEthical approval was received from the University of Witwatersrand Human Research Ethics Committee (HREC; ethics reference no. 200312) on August 20, 2020. This study is ongoing. Data collection has commenced and is expected to be completed in the second half of 2021. We will report on the machine-guided tool’s performance and usability, together with user satisfaction and recommendations for improvement. ConclusionsMachine-guided risk assessment tools can provide a cost-effective alternative to large-scale HIV screening and help in providing targeted counseling and testing to prevent the spread of HIV. Trial RegistrationSouth African National Clinical Trial Registry DOH-27-042021-679; https://sanctr.samrc.ac.za/TrialDisplay.aspx?TrialID=5545 International Registered Report Identifier (IRRID)DERR1-10.2196/3030