Biology subjects

Narra, H. P.

Publications and source records attributed to Narra, H. P..

3 recordsLinked to original sources

bioRxiv2025

A Humanized IFN-γ Mouse Model Reveals Skin Eschar Formation, Enhanced Susceptibility and Scrub Typhus Pathogenesis

Scrub typhus, caused by Orientia tsutsugamushi (Ot) bacteria, is a serious acute febrile illness associated with significant mortality. An estimated one million cases occur annually, with more than one billion people at risk. No effective vaccine is currently available, largely due to the complex Ot strain diversity and an incomplete understanding of protective immune mechanisms. To overcome these challenges, there is a critical need for a suitable animal model that mimics human disease through the natural route of infection via mites. Here, we report for the first time that a genetically engineered humanized mouse strain (with triple knockout/knock-in of IFN-{gamma} and its receptors), exhibits increased susceptibility to intradermal Ot infection compared to wild-type (WT) mice. This is evidenced by greater body weight loss, elevated bacterial burden, and reduced expression of interferon-stimulated genes (ISGs). Humanized mice exhibit pronounced biochemical abnormalities and tissue pathology accompanied by dysregulated T cell and neutrophil responses following infection. Notably, these immunocompetent mice develop skin eschar-like lesions resembling those observed in human patients. Overall, our study introduces a promising humanized mouse model to dissect the immunopathogenesis of scrub typhus and evaluate future vaccine candidates. Author SummaryScrub typhus is a serious disease caused by the obligately intracellular bacterium Ot that spreads to humans through the bite of larval mites called chiggers. It affects over a million people each year, primarily in Asia, and can lead to life-threatening complications. Unfortunately, we still lack a clear understanding of how this infection causes disease, partly because there is not a good laboratory model that closely reflects how humans respond to infection. Our recent reports have suggested an important role of IFN-{gamma} in host protection against Ot infection. In this study, we used a new genetically modified mouse strain that carries human IFN-{gamma} signaling in place of its mouse counterpart. We found that these humanized mice are more vulnerable to infection, develop skin eschar lesions like those in patients, and show signs of systemic inflammation and organ damage. Their immune response also resembled what has been observed in human patients. This new mouse model can help scientists better understand the mechanisms as to how this bacterial species causes severe disease outcomes in patients. Once those mechanisms are understood, this mouse model will serve a further purpose as a tool for testing new vaccines and treatments to aid humans at-risk for scrub typhus.

immunology↗

bioRxiv2023

Microbiome variability of mosquito lines is consistent over time and across environments

The composition of the microbiome is shaped by both environment and host genetic background in most organisms, but in the mosquito Aedes aegypti the role of host genetics in shaping the microbiome is poorly understood. Previously, we had shown that four lines of Ae. aegypti harbored different microbiomes when reared in the same insectary under identical conditions. To determine whether these lines differed from each other across time and in different environments, we characterized the microbiome of the same four lines of Ae. aegypti reared in the original insectary and at another institution. While it was clear that the environment influenced the microbiomes of these lines, we did still observe distinct differences in the microbiome between lines within each insectary. Clear differences were observed in alpha diversity, beta diversity, and abundance of specific bacterial taxa. To determine if the line specific differences in the microbiome were maintained across environments, pair-wise differential abundances of taxa was compared between insectaries. Lines were most similar to other lines from the same insectary than to the same line reared in a different insectary. Additionally, relatively few differentially abundant taxa identified between pairs of lines were shared across insectaries, indicating that line specific properties of the microbiome are not conserved across environments, or that there were distinct microbiota within each insectary. Overall, these results demonstrate that mosquito line can shape the microbiome across microbially- diverse environments and host by microbe interactions affecting microbiome composition and abundance is dependent on environmentally available bacteria. Author SummaryThe mosquito microbiome plays a critical role in shaping interactions with human pathogens. The factors that contribute to shaping the composition of the mosquito microbiome are of high importance due to its role in pathogen interactions and the successful development of control strategies. In other organisms, both host genetics and environment shape the microbiome composition, but the role of host genetics in shaping the mosquito microbiome is less clear. Previously, we have shown that different lines of Aedes aegypti harbor different microbiomes when reared in the same environment. We were curious to see if these differences could still be detected after further generations in the same insectary and across environments in a different insectary. We found that found that the microbiome differed between these lines in each insectary indicating an element of both host genetic background and environment play a role in establishing the microbiome. Our results indicate that different genetic backgrounds of Ae. aegypti will interact with their environment differently to shape their microbiome, which could potentially influence interactions with human pathogens and/or the effectiveness of control strategies. More broadly, our results are of interest for the ecology of host-microbe interactions.

microbiology↗

bioRxiv2018

CRISPR/Cas9-mediated gene deletion of the ompA gene in an Enterobacter gut symbiont impairs biofilm formation and reduces gut colonization of Aedes aegypti mosquitoes

BackgroundSymbiotic bacteria are pervasive in mosquitoes and their presence can influence many host phenotypes that affect vectoral capacity. While it is evident that environmental and host genetic factors contribute in shaping the microbiome of mosquitoes, we have a poor understanding regarding how bacterial genetics affects colonization of the mosquito gut. The CRISPR/Cas9 gene editing system is a powerful tool to alter bacterial genomes facilitating investigations into host-microbe interactions but has yet to be applied to insect symbionts. Methodology/Principal FindingsTo investigate the role of bacterial factors in mosquito biology and in colonization of mosquitoes we used CRISPR/Cas9 gene editing system to mutate the outer membrane protein A (ompA) gene of an Enterobacter symbiont isolated from Aedes mosquitoes. The ompA mutant had an impaired ability to form biofilms and poorly infected Ae. aegypti when reared in a mono-association under gnotobiotic conditions. In adults the mutant had a significantly reduced infection prevalence compared to the wild type or complement strains, while no differences in prevalence were seen in larvae, suggesting bacterial genetic factors are particularly important for adult gut colonization. We also used the CRISPR/Cas9 system to integrate genes (antibiotic resistance and fluorescent markers) into these symbionts genome and demonstrated that these genes were functional in vitro and in vivo. Conclusions/SignificanceOur results shed insights onto the role of ompA gene in host-microbe interactions in Ae. aegypti and confirm that CRISPR/Cas9 gene editing can be employed for genetic manipulation of non-model gut microbes. The ability to use this technology for site-specific integration of genes into the symbiont will facilitate the development of paratransgenic control strategies to interfere with arboviral pathogens such Chikungunya, dengue, Zika and Yellow fever viruses transmitted by Aedes mosquitoes. Author summaryMicrobiota profoundly affect their host but few studies have investigated the role of bacterial genetics in host-microbe interactions in mosquitoes. Here we applied the CRISPR/Cas9 gene editing system to knock out a membrane protein in Enterobacter, which is a dominant member of the mosquito microbiome. The mutant strain lacked the capacity to form biofilms, infected larvae and adults at lower titers, and had a reduced prevalence in adults. The lower prevalence in adults, but not larvae, likely reflects the difference in the modes of bacterial acquisition from the larval water of these two life stages. Importantly from an applied perspective, we also demonstrated that this editing technology can be harnessed for site-specific integration of genes into the bacterial chromosome. In proof-of-principle studies we integrated either a fluorescent protein or gene conferring antibiotic resistance into the bacterial genome and showed these transgenes were functional in mosquitoes. The specificity, flexibility, and simplicity of this editing approach in non-model bacteria will be useful for developing novel symbiotic control strategies to control arthropod-borne disease.

microbiology↗