Biology subjects

Dionne, M. S.

Publications and source records attributed to Dionne, M. S..

12 recordsLinked to original sources

bioRxiv2024

Acquisition of daptomycin resistance in patients results in decreased virulence in Drosophila

Staphylococcus aureus can acquire antimicrobial resistance which in turn may affect its pathogenic potential. Using a panel of paired clinical isolates collected before and after daptomycin resistance acquisition, most frequently through single mprF mutation, we show a relationship between increasing daptomycin minimum inhibitory concentration and reduced virulence in a Drosophila systemic infection model. Analysing toxin production, in vitro bacterial growth characteristics, and cell surface properties, we failed to link daptomycin resistance-related attenuated virulence to either reduced virulence factor production, reduced fitness or to any of the cell surface characteristics investigated. Competition assays in Drosophila also did not support any altered ability in immune evasion. Instead, using a panel of mutant flies defective for various immune components, we show that this daptomycin resistance-related attenuated virulence is mostly explained by greater susceptibility to activity of Drosophila prophenoloxidase, a tyrosinase involved in melanization, but not to antimicrobial peptides or to Bomanin antimicrobial effectors. Further investigation could not link daptomycin resistance-related attenuation of virulence to a differential susceptibility to reactive oxygen species or to quinones prominently associated with phenoloxidase bacterial-killing activity. Taken together, it appears that daptomycin resistance attenuates Staphylococcus aureus virulence through an enhanced sensitivity to phenoloxidase based on a complex mechanism. Our study provides new insights in the understanding of the crosstalk between antimicrobial resistance, escape from immune killing, and virulence. Author summaryAcquiring antimicrobial resistance can increase or decrease bacterial virulence. However, the mechanisms causing these resistance-virulence linked effects are unclear. Here, we bring new insights on the crosstalk between antimicrobial resistance and virulence. We characterized a panel of Staphylococcus aureus strains isolated from patients before and after resistance acquisition to the antibiotic daptomycin. Relative to the parental strain, resistant isolates most often varied by one single mutation, in a gene involved in the composition of the bacterial membrane, and these strains were much less virulent when fruit-flies were infected. Our results indicate that the difference of virulence is unrelated to changes in bacterial toxin production, bacterial growth, immune evasion or cell surface properties. Instead, resistant strains were more vulnerable to a host proenzyme involved in the antibacterial melanization response, an important response deployed throughout the arthropods. We predict that daptomycin resistance forces staphylococci to alter the composition of their cell surface. This alteration causes the bacteria to become more vulnerable to killing by melanization. Our results contribute to our understanding of the link between antimicrobial resistance and pathogenicity.

microbiology↗

bioRxiv2023

High sugar diets can increase susceptibility to bacterial infection in Drosophila melanogaster

Overnutrition with dietary sugar can worsen infection outcomes in diverse organisms including insects and humans, generally through unknown mechanisms. In the present study, we show that adult Drosophila melanogaster fed high-sugar diets became more susceptible to infection by the Gram-negative bacteria Providencia rettgeri and Serratia marcescens, although diet had no significant effect on infection by Gram-positive bacteria Enterococcus faecalis or Lactococcus lactis. We found that P. rettgeri and S. marcescens proliferate more rapidly in D. melanogaster fed a high-sugar diet, resulting in increased probability of host death. D. melanogaster become hyperglycemic on the high-sugar diet, and we find evidence that the extra carbon availability may promote S. marcescens growth within the host. However, we found no evidence that increased carbon availability directly supports greater P. rettgeri growth. D. melanogaster on both diets fully induce transcription of antimicrobial peptide (AMP) genes in response to infection, but D. melanogaster provided with high-sugar diets show reduced production of AMP protein. Thus, overnutrition with dietary sugar may impair host immunity at the level of AMP translation. Our results demonstrate that dietary sugar can shape infection dynamics by impacting both host and pathogen, depending on the nutritional requirements of the pathogen and by altering the physiological capacity of the host to sustain an immune response. Author SummaryDiet has critical impact on the quality of immune defense, and high-sugar diets increase susceptibility to bacterial infection in many animals. Yet it is unknown which aspects of host and pathogen physiology are impacted by diet to influence infection dynamics. Here we show that high-sugar diets increase susceptibility to some, but not all, bacterial infections in Drosophila. We find that feeding on high sugar diet impairs the host immune response by reducing the level of antimicrobial peptides produced. The expression of genes encoding these peptides is not affected, so we infer that protein translation is impaired. We further show that flies on high-sugar diets are hyperglycemic, and that some pathogens may use the excess sugar in the host to promote growth during the infection. Thus, our study demonstrates that dietary impacts on infection outcome arise through physiological effects on both the host and pathogen.

immunology↗

bioRxiv2023

A humoral stress response protects Drosophila tissues from antimicrobial peptides

The immune response against an invading pathogen is generally associated with collateral tissue damage caused by the immune system itself. Consequently, several resilience mechanisms have evolved to attenuate the negative impacts of immune effectors. Antimicrobial peptides (AMPs) are small, cationic peptides that contribute to innate defenses by targeting negatively charged membranes of microbes1, 2. While being protective against pathogens, AMPs can be cytotoxic to host cells1, 3. Little is known of mechanisms that protect host tissues from AMP-induced immunopathology. Here, we reveal that a family of stress-induced proteins, the Turandots4, 5, protect Drosophila host tissues from AMPs, increasing resilience to stress. Deletion of several Turandot genes increases fly susceptibility to environmental stresses due to trachea apoptosis and poor oxygen supply. Tracheal cell membranes expose high levels of phosphatidylserine, a negatively charged phospholipid, sensitizing them to the action of AMPs. Turandots are secreted from the fat body upon stress and bind to tracheal cells to protect them against AMPs. In vitro, Turandot A binds to phosphatidylserine on membranes and inhibits the pore-forming activity of Drosophila and human AMPs on eukaryotic cells without affecting their microbicidal activity. Collectively, these data demonstrate that Turandot stress proteins mitigate AMP cytotoxicity to host tissues and therefore improve their efficacy. This provides a first example of a humoral mechanism used by animals limiting host-encoded AMP collateral damages.

immunology↗

bioRxiv2023

Drosophila macrophages control systemic cytokine levels in response to oxidative stress via a non-canonical DNA damage repair signaling cascade

Environmental factors, infection, or injury can cause oxidative stress in diverse tissues and loss of tissue homeostasis. Effective stress response cascades, conserved from invertebrates to mammals, ensure reestablishment of homeostasis and tissue repair. Hemocytes, the Drosophila blood-like cells, rapidly respond to oxidative stress by immune activation. However, the precise signals how they sense oxidative stress and integrate these signals to modulate and balance the response to oxidative stress in the adult fly are ill-defined. Furthermore, hemocyte diversification was not explored yet on oxidative stress. Here, we employed high throughput single nuclei RNA-sequencing to explore hemocytes and other cell types, such as fat body, during oxidative stress in the adult fly. We identified distinct cellular responder states in plasmatocytes, the Drosophila macrophages, associated with immune response and metabolic activation upon oxidative stress. We further define oxidative stress-induced DNA damage signaling as a key sensor and a rate-limiting step in immune-activated plasmatocytes controlling JNK-mediated release of the pro-inflammatory cytokine unpaired-3. We subsequently tested the role of this specific immune activated cell stage during oxidative stress and found that inhibition of DNA damage signaling in plasmatocytes, as well as JNK or upd3 overactivation, result in a higher susceptibility to oxidative stress. Our findings uncover that a balanced composition and response of hemocyte subclusters is essential for the survival of adult Drosophila on oxidative stress by regulating systemic cytokine levels and cross-talk to other organs, such as the fat body, to control energy mobilization.

immunology↗

bioRxiv2022

A serine-folate metabolic unit controls resistance and tolerance of infection

Immune activation drives metabolic change in most animals. Immune-induced metabolic change is most conspicuous as a driver of pathology in serious or prolonged infection, but it is normally expected to be important to support immune function and recovery. Many of the signalling mechanisms linking immune detection with metabolic regulation, and their specific consequences, are unknown. Here, we show that Drosophila melanogaster respond to many bacterial infections by altering expression of genes of the folate cycle and associated enzymes of amino acid metabolism. The net result of these changes is increased flow of carbon from glycolysis into serine and glycine synthesis and a shift of folate cycle activity from the cytosol into the mitochondrion. Immune-induced transcriptional induction of astray and Nmdmc, the two most-induced of these enzymes, depends on Dif and foxo. Loss of astray or Nmdmc results in infection-specific immune defects. Our work thus shows a key mechanism that connects immune-induced changes in metabolic signalling with the serine-folate metabolic unit to result in changed immune function.

immunology↗

bioRxiv2022

E. faecalis acquires resistance to antimicrobials and insect immunity via common mechanisms

Enterococcus faecalis is a normal member of the gut microbiota and an opportunistic pathogen of many animals, including mammals, birds, and insects. It is a common cause of nosocomial infections, and is particularly troublesome due to extensive intrinsic and acquired antimicrobial resistance. Using experimental evolution, we generated Drosophila-adapted E. faecalis strains, which exhibited immune resistance, resulting in increased in vivo growth and virulence. Resistance was characterised by mutations in bacterial pathways responsive to cell envelope stress. Drosophila-adapted strains exhibited changes in sensitivity to relevant antimicrobials, including daptomycin and vancomycin. Evolved daptomycin-resistant strains harboured mutations in the same signalling systems, with some strains showing increased virulence similar to Drosophila-adapted strains. Our results show that common mechanisms provide a route to resistance to both antimicrobials and host immunity in E. faecalis and demonstrate that the selection and emergence of antibiotic resistance in vivo does not require antibiotic exposure. One sentence summaryHost interaction can promote antimicrobial resistance and antimicrobial treatment can promote virulence in E. faecalis.

microbiology↗

bioRxiv2021

The pathobiology of Mycobacterium abscessus revealed through phenogenomic analysis

The medical and scientific response to emerging pathogens is often severely hampered by ignorance of the genetic determinants of virulence, drug resistance, and clinical outcomes that could be used to identify therapeutic drug targets and forecast patient trajectories 1-5. Taking the newly emergent multidrug-resistant bacteria Mycobacterium abscessus as an example 6, we show that combining high dimensional phenotyping with whole genome sequencing in a phenogenomic analysis can rapidly reveal actionable systems-level insights into bacterial pathobiology. Using in vitro and in vivo phenotyping, we discovered three distinct clusters of isolates, each associated with a different clinical outcome. We combined genome-wide association studies (GWAS) with proteome-wide computational structural modelling 7 to define likely causal variants, and employed direct coupling analysis (DCA) 8 to identify co-evolving, and therefore potentially epistatic, gene networks. We then used in vivo CRISPR-based silencing to validate our findings, defining a novel secretion system controlling virulence in M. abscessus, and illustrating how phenogenomics can reveal critical pathways within emerging pathogenic bacteria.

microbiology↗

bioRxiv2021

Pre-copulatory reproductive behaviours are preserved in Drosophila melanogaster infected with bacteria.

Reproduction and immunity are crucial traits that determine an animals fitness. Terminal investment hypothesis predicts that reproductive investment should increase in the face of a mortality risk caused by infection. However, due to competitive allocation of energetic resources, individuals fighting infections are expected to decrease reproductive efforts. While there is evidence for both hypotheses, the factors that determine the choice between these strategies are poorly understood. Here, we assess the impact of bacterial infection on pre-copulatory behaviours in the fruit fly Drosophila melanogaster. We found that male flies infected with six different bacteria, including pathogenic and non-pathogenic strains, show no significant differences in courtship intensity and mating success. Similarly, bacterial infections did not affect sexual receptivity in female flies. Our data suggest that pre-copulatory reproductive behaviours remain preserved in infected animals, despite the huge metabolic cost of infection.

animal behavior and cognition↗

bioRxiv2021

Infection increases activity via Toll dependent and independent mechanisms in Drosophila melanogaster

Host behavioural changes are among the most apparent effects of infection. Sickness behaviour can involve a variety of symptoms, including anorexia, depression, and changed activity levels. Here we use a real-time tracking and behavioural profiling platform to show that, in Drosophila melanogaster, many systemic bacterial infections cause significant increases in physical activity, and that the extent of this activity increase is a predictor of survival time in several lethal infections. Using various bacteria and D. melanogaster immune and activity mutants, we show that increased activity is driven by at least two different mechanisms. Increased activity after infection with Micrococcus luteus, a Gram-positive bacterium rapidly cleared by the immune response, strictly requires the Toll ligand spatzle and Toll-pathway activity in the fat body and the brain. In contrast, increased activity after infection with Francisella novicida, a Gram-negative bacterium that cannot be cleared by the immune response, is entirely independent of either spatzle or the parallel IMD pathway. The existence of multiple signalling mechanisms by which bacterial infections drive increases in physical activity implies that this effect may be an important aspect of the host response.

immunology↗

bioRxiv2020

Disparate regulation of imd drives sex differences in infection tolerance in Drosophila melanogaster

Male and female animals exhibit differences in infection outcomes. One possible source of sexually dimorphic immunity is sex-specific costs of immune activity or pathology, but little is known about the independent effects of immune-induced versus microbe-induced pathology, and whether these may differ for the sexes. Here, through measuring metabolic and physiological outputs in wild-type and immune-compromised Drosophila melanogaster, we test whether the sexes are differentially impacted by these various sources of pathology and identify a critical regulator of this difference. We find that the sexes exhibit differential immune activity but similar bacteria-derived metabolic pathology. We show that female-specific immune-inducible expression of PGRP-LB, a negative regulator of the Imd pathway, enables females to reduce immune activity in response to reductions in bacterial numbers. In the absence of PGRP-LB, females are more resistant of infection, confirming the functional importance of this regulation and suggesting that female-biased immune restriction comes at a cost.

immunology↗

bioRxiv2020

EslB is required for cell wall Integrity and cell division in Listeria monocytogenes

Lysozyme is an important component of the innate immune system. It functions by hydrolysing the peptidoglycan (PG) layer of bacteria. The human pathogen Listeria monocytogenes is intrinsically lysozyme resistant. The peptidoglycan N-deacetylase PgdA and O-acetyltransferase OatA are two known factors contributing to its lysozyme resistance. Furthermore, it was shown that the absence of components of an ABC transporter, here referred to as EslABC, leads to reduced lysozyme resistance. How its activity is linked to lysozyme resistance is still unknown. To investigate this further, a strain with a deletion in eslB, coding for a membrane component of the ABC transporter, was constructed in L. monocytogenes strain 10403S. The eslB mutant showed a 40-fold reduction in the minimal inhibitory concentration to lysozyme. Analysis of the PG structure revealed that the eslB mutant produced PG with reduced levels of O-acetylation. Using growth and autolysis assays, we show that the absence of EslB manifests in a growth defect in media containing high concentrations of sugars and increased endogenous cell lysis. A thinner PG layer produced by the eslB mutant under these growth conditions might explain these phenotypes. Furthermore, the eslB mutant had a noticeable cell division defect and formed elongated cells. Microscopy analysis revealed that an early cell division protein still localized in the eslB mutant indicating that a downstream process is perturbed. Based on our results, we hypothesize that EslB affects the biosynthesis and modification of the cell wall in L. monocytogenes and is thus important for the maintenance of cell wall integrity. IMPORTANCEThe ABC transporter EslABC is associated with the intrinsic lysozyme resistance of Listeria monocytogenes. However, the exact role of the transporter in this process and in the physiology of L. monocytogenes is unknown. Using different assays to characterize an eslB deletion strain, we found that the absence of EslB not only affects lysozyme resistance, but also endogenous cell lysis, cell wall biosynthesis, cell division and the ability of the bacterium to grow in media containing high concentrations of sugars. Our results indicate that EslB is by a yet unknown mechanism an important determinant for cell wall integrity in L. monocytogenes.

microbiology↗

bioRxiv2019

Muscle function and homeostasis require macrophage-derived cytokine inhibition of AKT activity in Drosophila

Unpaired ligands are secreted signals that act via a GP130-like receptor, domeless, to activate JAK-STAT signaling in Drosophila. Like many mammalian cytokines, unpaireds can be activated by infection and other stresses and can promote insulin resistance in target tissues. However, the importance of this effect in non-inflammatory physiology is unknown. Here, we identify a requirement for unpaired-JAK signaling as a metabolic regulator in healthy adult Drosophila muscle. Adult muscles show basal JAK-STAT signaling activity in the absence of any immune challenge. Macrophages are the source of much of this tonic signal. Loss of the dome receptor on adult muscles significantly reduces lifespan and causes local and systemic metabolic pathology. These pathologies result from hyperactivation of AKT and consequent deregulation of metabolism. Thus, we identify a cytokine signal from macrophages to muscle that controls AKT activity and metabolic homeostasis.

developmental biology↗