Biology subjects

Higgs, M. G.

Publications and source records attributed to Higgs, M. G..

3 recordsLinked to original sources

bioRxiv2025

Role of Thioredoxin Reductase (TrxB) in Oxidative Stress Response of Francisella tularensis Live Vaccine Strain

Francisella tularensis is an important human pathogen responsible for causing tularemia in the Northern Hemisphere. Francisella has been developed as a biological weapon in the past due to its extremely high virulence. F. tularensis is a Gram-negative, intracellular pathogen that primarily infects macrophages. To counteract the reactive oxygen and nitrogen species (ROS/RNS) produced by macrophages in response to infection, F. tularensis encodes a repertoire of antioxidant enzymes. Among these, the thioredoxin system is critical for maintaining cellular redox homeostasis by regulating the balance between oxidation and reduction within bacterial cells. This system includes thioredoxins, thioredoxin reductase, and NADPH. Despite its potential importance, the thioredoxin system of F. tularensis remains understudied. F. tularensis possesses two thioredoxin genes, trxA1 (FTL_0611) and trxA2 (FTL_1224), and a single thioredoxin reductase gene, trxB (FTL_1571). In this study, we characterized the role of trxB in oxidative stress resistance. Our findings demonstrate that trxB is essential for oxidative stress resistance in F. tularensis and that its loss increases susceptibility to several antibiotics. However, unlike in other bacterial species, TrxB in F. tularensis is not a functional target of the gold-containing antimicrobial agent auranofin. We also show that OxyR, the master regulator of oxidative stress responses, directly controls trxB expression under oxidative stress conditions. Furthermore, TrxB contributes to intramacrophage survival by enabling the bacterium to withstand ROS-induced oxidative stress. Collectively, this study highlights a critical, previously uncharacterized antioxidant defense mechanism in F. tularensis, highlighting its importance in oxidative stress resistance and intramacrophage survival.

microbiology↗

bioRxiv2024

Flagellar motility and the mucus environment influence aggregation mediated antibiotic tolerance of Pseudomonas aeruginosa in chronic lung infection

Pseudomonas aeruginosa frequently causes chronic lung infection in individuals with muco-obstructive airway diseases (MADs). Chronic P. aeruginosa infections are difficult to treat, primarily owing to antibiotic treatment failure, which is often observed in the absence of antimicrobial resistance. In MADs, P. aeruginosa forms biofilm-like aggregates within the luminal mucus. While the contribution of mucin hyperconcentration towards antibiotic tolerance has been described, the mechanism for mucin driven antibiotic tolerance and the influence of aggregates have not been fully elucidated. In this study, we investigated the contribution of flagellar motility towards aggregate formation as it relates to the diseased mucus environment. We found that loss of flagellar motility resulted in increased P. aeruginosa aggregation and tolerance to multiple classes of antibiotics. Further, we observed differential roles in antimicrobial tolerance of the motAB and motCD stators, which power the flagellum. Additionally, we found that control of fliC expression was important for aggregate formation and antibiotic tolerance as a strain constitutively expressing fliC was unable to form aggregates and was highly susceptible to treatment. Lastly, we demonstrate that neutrophil elastase, an abundant immune mediator and biomarker of chronic lung infection, promotes aggregation and antibiotic tolerance by impairing flagellar motility. Collectively, these results highlight the key role of flagellar motility in aggregate formation and antibiotic tolerance and deepens our understanding of how the MADs lung environment promotes antibiotic tolerance of P. aeruginosa. IMPORTANCEAntibiotic recalcitrance of chronic Pseudomonas aeruginosa infections in muco-obstructive airway diseases is a primary driver of mortality. Mechanisms that drive antibiotic tolerance are poorly understood. We investigated motility phenotypes related to P. aeruginosa adaptation and antibiotic tolerance in the diseased mucus environment. Loss of flagellar motility drives antibiotic tolerance by promoting aggregate formation. Regulation of flagellar motility appears to be a key step in aggregate formation as the inability to turn off flagellin expression resulted in poor aggregate formation and increased antibiotic susceptibility. These results deepen our understanding of the formation of antibiotic tolerant aggregates within the MADs airway and opens novel avenues and targets for treatment of chronic P. aeruginosa infections.

microbiology↗

bioRxiv2023

Mucus polymer concentration and in vivo adaptation converge to define the antibiotic response of Pseudomonas aeruginosa during chronic lung infection

The airway milieu of individuals with muco-obstructive airway diseases (MADs) is defined by the accumulation of dehydrated mucus due to hyperabsorption of airway surface liquid and defective mucociliary clearance. Pathological mucus becomes progressively more viscous with age and disease severity due to the concentration and overproduction of mucin and accumulation of host-derived extracellular DNA (eDNA). Respiratory mucus of MADs provides a niche for recurrent and persistent colonization by respiratory pathogens, including Pseudomonas aeruginosa, which is responsible for the majority of morbidity and mortality in MADs. Despite high concentration inhaled antibiotic therapies and the absence of antibiotic resistance, antipseudomonal treatment failure in MADs remains a significant clinical challenge. Understanding the drivers of antibiotic recalcitrance is essential for developing more effective treatments that eradicate persistent infections. The complex and dynamic environment of diseased airways makes it difficult to model antibiotic efficacy in vitro. We aimed to understand how mucin and eDNA concentrations, the two dominant polymers in respiratory mucus, alter the antibiotic tolerance of P. aeruginosa. Our results demonstrate that polymer concentration and molecular weight affect P. aeruginosa survival post antibiotic challenge. Polymer-driven antibiotic tolerance was not explicitly associated with reduced antibiotic diffusion. Lastly, we established a robust and standardized in vitro model for recapitulating the ex vivo antibiotic tolerance of P. aeruginosa observed in expectorated sputum across age, underlying MAD etiology, and disease severity, which revealed the inherent variability in intrinsic antibiotic tolerance of host-evolved P. aeruginosa populations. ImportanceAntibiotic treatment failure in Pseudomonas aeruginosa chronic lung infections is associated with increased morbidity and mortality, illustrating the clinical challenge of bacterial infection control. Understanding the underlying infection environment, as well as the host and bacterial factors driving antibiotic tolerance and the ability to accurately recapitulate these factors in vitro, is crucial for improving antibiotic treatment outcomes. Here, we demonstrate that increasing concentration and molecular weight of mucin and host eDNA drive increased antibiotic tolerance to tobramycin. Through systematic testing and modeling, we identified a biologically relevant in vitro condition that recapitulates antibiotic tolerance observed in ex vivo treated sputum. Ultimately, this study revealed a dominant effect of in vivo evolved bacterial populations in defining inter-subject ex vivo antibiotic tolerance and establishes a robust and translatable in vitro model for therapeutic development.

microbiology↗