Syndecan-1 Promotes Streptococcus pneumoniae Corneal Infection by Facilitating the Assembly of Adhesive Fibronectin Fibrils

ABSTRACT Subversion of heparan sulfate proteoglycans (HSPGs) is thought to be a common virulence mechanism shared by many microbial pathogens. The prevailing assumption is that pathogens co-opt HSPGs as cell surface attachment receptors or as inhibitors of innate host defense. However, there are few data that clearly support this idea in vivo. We found that deletion of syndecan-1 (Sdc1), a major cell surface HSPG of epithelial cells, causes a gain of function in a mouse model of scarified corneal infection, where Sdc1−/− corneas were significantly less susceptible to Streptococcus pneumoniae infection. Administration of excess Sdc1 ectodomains significantly inhibited S. pneumoniae corneal infection, suggesting that Sdc1 promotes infection as a cell surface attachment receptor. However, S. pneumoniae did not interact with Sdc1 and Sdc1 was shed upon S. pneumoniae infection, indicating that Sdc1 does not directly support S. pneumoniae adhesion. Instead, Sdc1 promoted S. pneumoniae adhesion by driving the assembly of fibronectin (FN) fibrils in the corneal basement membrane to which S. pneumoniae attaches when infecting injured corneas. S. pneumoniae specifically bound to corneal FN via PavA, and PavA deletion significantly attenuated S. pneumoniae virulence in the cornea. Excess Sdc1 ectodomains inhibited S. pneumoniae corneal infection by binding to the Hep II domain and interfering with S. pneumoniae PavA binding to FN. These findings reveal a previously unknown virulence mechanism of S. pneumoniae where key extracellular matrix (ECM) interactions and structures that are essential for host cell homeostasis are exploited for bacterial pathogenesis. IMPORTANCE Bacterial pathogens have evolved several ingenious mechanisms to subvert host cell biology for their pathogenesis. Bacterial attachment to the host ECM establishes a niche to grow and is considered one of the critical steps of infection. This pathogenic mechanism entails coordinated assembly of the ECM by the host to form the ECM structure and organization that are specifically recognized by bacteria for their adhesion. We serendipitously discovered that epithelial Sdc1 facilitates the assembly of FN fibrils in the corneal basement membrane and that this normal biological function of Sdc1 has detrimental consequences for the host in S. pneumoniae corneal infection. Our studies suggest that bacterial subversion of the host ECM is more complex than previously appreciated.

Download Full-text

Posttranscriptional Control of Microbe-Induced Rearrangement of Host Cell Actin

mBio ◽

10.1128/mbio.01025-13 ◽

2014 ◽

Vol 5 (1) ◽

Cited By ~ 35

Author(s):

Charley C. Gruber ◽

Vanessa Sperandio

Keyword(s):

Escherichia Coli ◽

Host Cell ◽

Type Iii Secretion ◽

Cell Biology ◽

Molecular Mechanisms ◽

Bacterial Attachment ◽

Posttranscriptional Control ◽

Content Type ◽

Type Iii ◽

Pedestal Formation

ABSTRACTRemodeling of the host cytoskeleton is a common strategy employed by bacterial pathogens. Although there is vigorous investigation of the cell biology underlying these bacterially mediated cytoskeleton modifications, knowledge of the plasticity and dynamics of the bacterial signaling networks that regulate the expression of genes necessary for these phenotypes is lacking. EnterohemorrhagicEscherichia coliattaches to enterocytes, forming pedestal-like structures. Pedestal formation requires the expression of the locus-of-enterocyte-effacement (LEE) andespFugenes. The LEE encodes a molecular syringe, a type III secretion system (T3SS) used by pathogens to translocate effectors such as EspFu into the host cell. By using a combination of genetic, biochemical, and cell biology approaches, we show that pedestal formation relies on posttranscriptional regulation by two small RNAs (sRNAs), GlmY and GlmZ. The GlmY and GlmZ sRNAs are unique; they have extensive secondary structures and work in concert. Although these sRNAs may offer unique insights into RNA and posttranscriptional biology, thus far, only one target and one mechanism of action (exposure of the ribosome binding site from theglmSgene to promote its translation) has been described. Here we uncovered new targets and two different molecular mechanisms of action of these sRNAs. In the case of EspFu expression, they promote translation by cleavage of the transcript, while in regard to the LEE, they promote destabilization of the mRNA. Our findings reveal that two unique sRNAs act in concert through different molecular mechanisms to coordinate bacterial attachment to mammalian cells.IMPORTANCEPathogens evolve by horizontal acquisition of pathogenicity islands. We describe here how two sRNAs, GlmY and GlmZ, involved in cellular metabolism and cellular architecture, through the posttranscriptional control of GlmS (the previously only known target of GlmY and GlmZ), which controls amino sugar synthesis, have been coopted to modulate the expression of virulence. These sRNAs quickly allow for plasticity in gene expression in order for enterohemorrhagicEscherichia colito fine-tune the expression of its complex type III secretion machinery and its effectors to promote bacterial attachment and subsequent actin rearrangement on host cells. Pedestal formation is a very dynamic process. Many of the genes necessary for pedestal formation are located within the same operon to evolutionarily guarantee that they are inherited together. However, it is worth noting that within these operons, several genes need to yield more proteins than others and that these differences cannot be efficiently regulated at the transcriptional level.

Download Full-text

Surface Association of Pht Proteins of Streptococcus pneumoniae

Infection and Immunity ◽

10.1128/iai.00562-13 ◽

2013 ◽

Vol 81 (10) ◽

pp. 3644-3651 ◽

Cited By ~ 22

Author(s):

Charles D. Plumptre ◽

Abiodun D. Ogunniyi ◽

James C. Paton

Keyword(s):

Streptococcus Pneumoniae ◽

Cell Surface ◽

Significant Degree ◽

Surface Proteins ◽

Wild Type ◽

Surface Attachment ◽

Content Type ◽

Amino Acid Region ◽

Culture Supernatants

ABSTRACTStreptococcus pneumoniaeis a major human pathogen responsible for massive global morbidity and mortality. The pneumococcus attaches a variety of proteins to its cell surface, many of which contribute to virulence; one such family are the polyhistidine triad (Pht) proteins PhtA, PhtB, PhtD, and PhtE. In this study, we have examined the mechanism of Pht surface attachment using PhtD as a model. Analysis of deletion and point mutants identified a three-amino-acid region of PhtD (Q27-H28-R29) that is critical for the process. The analogous region in PhtE was also necessary for its attachment to the cell surface. Furthermore, we show that a large proportion of the total amount of each Pht protein is released into bacterial culture supernatants. Other surface proteins were also released, albeit to lesser extents, and this was not due to pneumococcal autolysis. The extent of release of surface proteins was strain dependent and was not affected by the capsule. Lastly, we compared the fitness of wild-type and ΔphtABDEpneumococciin vivoin a mouse coinfection model. Release of Pht proteins by the wild type did not complement the mutant strain, consistent with surface-attached rather than soluble forms of the Pht proteins playing the major role in virulence. The significant degree of release of Pht proteins from intact bacteria may have implications for the use of these proteins in novel vaccines.

Download Full-text

EtpE Binding to DNase X Induces Ehrlichial Entry via CD147 and hnRNP-K Recruitment, Followed by Mobilization of N-WASP and Actin

mBio ◽

10.1128/mbio.01541-15 ◽

2015 ◽

Vol 6 (6) ◽

Cited By ~ 12

Author(s):

Dipu Mohan Kumar ◽

Mingqun Lin ◽

Qingming Xiong ◽

Mathew James Webber ◽

Comert Kural ◽

...

Keyword(s):

Cell Surface ◽

Host Cell ◽

Actin Polymerization ◽

Ehrlichia Chaffeensis ◽

Content Type ◽

Hnrnp K ◽

Obligate Intracellular ◽

Human Proteins ◽

Coated Bead ◽

Human Monocytic Ehrlichiosis

ABSTRACTObligate intracellular bacteria, such asEhrlichia chaffeensis, perish unless they can enter eukaryotic cells.E. chaffeensisis the etiological agent of human monocytic ehrlichiosis, an emerging infectious disease. To infect cells,Ehrlichiauses theCterminus of the outer membrane invasinentry-triggeringprotein (EtpE) ofEhrlichia(EtpE-C), which directly binds the mammalian cell surface glycosylphosphatidyl inositol-anchored protein, DNase X. How this binding drivesEhrlichiaentry is unknown. Here, using affinity pulldown of host cell lysates with recombinant EtpE-C (rEtpE-C), we identified two new human proteins that interact with EtpE-C: CD147 and heterogeneous nuclear ribonucleoprotein K (hnRNP-K). The interaction of CD147 with rEtpE-C was validated by far-Western blotting and coimmunoprecipitation of native EtpE with endogenous CD147. CD147 was ubiquitous on the cell surface and also present around foci of rEtpE-C-coated-bead entry. Functional neutralization of surface-exposed CD147 with a specific antibody inhibitedEhrlichiainternalization and infection but not binding. Downregulation of CD147 by short hairpin RNA (shRNA) impairedE. chaffeensisinfection. Functional ablation of cytoplasmic hnRNP-K by a nanoscale intracellular antibody markedly attenuated bacterial entry and infection but not binding. EtpE-C also interacted with neuronal Wiskott-Aldrich syndrome protein (N-WASP), which is activated by hnRNP-K. Wiskostatin, which inhibits N-WASP activation, and cytochalasin D, which inhibits actin polymerization, inhibitedEhrlichiaentry. Upon incubation with host cell lysate, EtpE-C but not an EtpE N-terminal fragment stimulatedin vitroactin polymerization in an N-WASP- and DNase X-dependent manner. Time-lapse video images revealed N-WASP recruitment at EtpE-C-coated bead entry foci. Thus, EtpE-C binding to DNase X drivesEhrlichiaentry by engaging CD147 and hnRNP-K and activating N-WASP-dependent actin polymerization.IMPORTANCEEhrlichia chaffeensis, an obligate intracellular bacterium, causes a blood-borne disease called human monocytic ehrlichiosis, one of the most prevalent life-threatening emerging tick-transmitted infectious diseases in the United States. The survival ofEhrlichiabacteria, and hence, their ability to cause disease, depends on their specific mode of entry into eukaryotic host cells. Understanding the mechanism by whichE. chaffeensisenters cells will create new opportunities for developing effective therapies to prevent bacterial entry and disease in humans. Our findings reveal a novel cellular signaling pathway triggered by an ehrlichial surface protein called EtpE to induce its infectious entry. The results are also important from the viewpoint of human cell physiology because three EtpE-interacting human proteins, DNase X, CD147, and hnRNP-K, are hitherto unknown partners that drive the uptake of small particles, including bacteria, into human cells.

Download Full-text

Chicken Juice Enhances Surface Attachment and Biofilm Formation of Campylobacter jejuni

Applied and Environmental Microbiology ◽

10.1128/aem.02614-14 ◽

2014 ◽

Vol 80 (22) ◽

pp. 7053-7060 ◽

Cited By ~ 68

Author(s):

Helen L. Brown ◽

Mark Reuter ◽

Louise J. Salt ◽

Kathryn L. Cross ◽

Roy P. Betts ◽

...

Keyword(s):

Campylobacter Jejuni ◽

Food Chain ◽

Biofilm Formation ◽

Cell Attachment ◽

Bacterial Attachment ◽

Poultry Meat ◽

Abiotic Surface ◽

Surface Attachment ◽

Aerobic Conditions ◽

Content Type

ABSTRACTThe bacterial pathogenCampylobacter jejuniis primarily transmitted via the consumption of contaminated foodstuffs, especially poultry meat. In food processing environments,C. jejuniis required to survive a multitude of stresses and requires the use of specific survival mechanisms, such as biofilms. An initial step in biofilm formation is bacterial attachment to a surface. Here, we investigated the effects of a chicken meat exudate (chicken juice) onC. jejunisurface attachment and biofilm formation. Supplementation of brucella broth with ≥5% chicken juice resulted in increased biofilm formation on glass, polystyrene, and stainless steel surfaces with fourC. jejuniisolates and oneC. coliisolate in both microaerobic and aerobic conditions. When incubated with chicken juice,C. jejuniwas both able to grow and form biofilms in static cultures in aerobic conditions. Electron microscopy showed thatC. jejunicells were associated with chicken juice particulates attached to the abiotic surface rather than the surface itself. This suggests that chicken juice contributes toC. jejunibiofilm formation by covering and conditioning the abiotic surface and is a source of nutrients. Chicken juice was able to complement the reduction in biofilm formation of an aflagellated mutant ofC. jejuni, indicating that chicken juice may support food chain transmission of isolates with lowered motility. We provide here a useful model for studying the interaction ofC. jejunibiofilms in food chain-relevant conditions and also show a possible mechanism forC. jejunicell attachment and biofilm initiation on abiotic surfaces within the food chain.

Download Full-text

The Distinct Immune-Stimulatory Capacities of Porphyromonas gingivalis Strains 381 and ATCC 33277 Are Determined by the fimB Allele and Gingipain Activity

Infection and Immunity ◽

10.1128/iai.00319-19 ◽

2019 ◽

Vol 87 (12) ◽

Author(s):

Stephen R. Coats ◽

Nutthapong Kantrong ◽

Thao T. To ◽

Sumita Jain ◽

Caroline A. Genco ◽

...

Keyword(s):

Cell Surface ◽

Immune Responses ◽

Host Cell ◽

Porphyromonas Gingivalis ◽

Stop Codon ◽

Premature Stop Codon ◽

Innate Immune ◽

Surface Proteins ◽

Innate Immune Responses ◽

Content Type

ABSTRACT The Porphyromonas gingivalis strain ATCC 33277 (33277) and 381 genomes are nearly identical. However, strain 33277 displays a significantly diminished capacity to stimulate host cell Toll-like receptor 2 (TLR2)-dependent signaling and interleukin-1β (IL-1β) production relative to 381, suggesting that there are strain-specific differences in one or more bacterial immune-modulatory factors. Genomic sequencing identified a single nucleotide polymorphism in the 33277 fimB allele (A→T), creating a premature stop codon in the 33277 fimB open reading frame relative to the 381 fimB allele. Gene exchange experiments established that the 33277 fimB allele reduces the immune-stimulatory capacity of this strain. Transcriptome comparisons revealed that multiple genes related to carboxy-terminal domain (CTD) family proteins, including the gingipains, were upregulated in 33277 relative to 381. A gingipain substrate degradation assay demonstrated that cell surface gingipain activity is higher in 33277, and an isogenic mutant strain deficient for the gingipains exhibited an increased ability to induce TLR2 signaling and IL-1β production. Furthermore, 33277 and 381 mutant strains lacking CTD cell surface proteins were more immune-stimulatory than the parental wild-type strains, consistent with an immune-suppressive role for the gingipains. Our data show that the combination of an intact fimB allele and limited cell surface gingipain activity in P. gingivalis 381 renders this strain more immune-stimulatory. Conversely, a defective fimB allele and high-level cell surface gingipain activity reduce the capacity of P. gingivalis 33277 to stimulate host cell innate immune responses. In summary, genomic and transcriptomic comparisons identified key virulence characteristics that confer divergent host cell innate immune responses to these highly related P. gingivalis strains.

Download Full-text

Lipid Anchoring of Archaeosortase Substrates and Midcell Growth in Haloarchaea

mBio ◽

10.1128/mbio.00349-20 ◽

2020 ◽

Vol 11 (2) ◽

Cited By ~ 6

Author(s):

Mohd Farid Abdul-Halim ◽

Stefan Schulze ◽

Anthony DiLucido ◽

Friedhelm Pfeiffer ◽

Alexandre Wilson Bisson Filho ◽

...

Keyword(s):

Cell Growth ◽

Cell Surface ◽

Cell Biology ◽

Fluorescent Protein ◽

De Novo ◽

Hot Spot ◽

Control Cell ◽

Haloferax Volcanii ◽

Surface Proteins ◽

Content Type

ABSTRACT The archaeal cytoplasmic membrane provides an anchor for many surface proteins. Recently, a novel membrane anchoring mechanism involving a peptidase, archaeosortase A (ArtA), and C-terminal lipid attachment of surface proteins was identified in the model archaeon Haloferax volcanii. ArtA is required for optimal cell growth and morphogenesis, and the S-layer glycoprotein (SLG), the sole component of the H. volcanii cell wall, is one of the targets for this anchoring mechanism. However, how exactly ArtA function and regulation control cell growth and morphogenesis is still elusive. Here, we report that archaeal homologs to the bacterial phosphatidylserine synthase (PssA) and phosphatidylserine decarboxylase (PssD) are involved in ArtA-dependent protein maturation. Haloferax volcanii strains lacking either HvPssA or HvPssD exhibited motility, growth, and morphological phenotypes similar to those of an ΔartA mutant. Moreover, we showed a loss of covalent lipid attachment to SLG in the ΔhvpssA mutant and that proteolytic cleavage of the ArtA substrate HVO_0405 was blocked in the ΔhvpssA and ΔhvpssD mutant strains. Strikingly, ArtA, HvPssA, and HvPssD green fluorescent protein (GFP) fusions colocalized to the midcell position of H. volcanii cells, strongly supporting that they are involved in the same pathway. Finally, we have shown that the SLG is also recruited to the midcell before being secreted and lipid anchored at the cell outer surface. Collectively, our data suggest that haloarchaea use the midcell as the main surface processing hot spot for cell elongation, division, and shape determination. IMPORTANCE The subcellular organization of biochemical processes in space and time is still one of the most mysterious topics in archaeal cell biology. Despite the fact that haloarchaea largely rely on covalent lipid anchoring to coat the cell envelope, little is known about how cells coordinate de novo synthesis and about the insertion of this proteinaceous layer throughout the cell cycle. Here, we report the identification of two novel contributors to ArtA-dependent lipid-mediated protein anchoring to the cell surface, HvPssA and HvPssD. ArtA, HvPssA, and HvPssD, as well as SLG, showed midcell localization during growth and cytokinesis, indicating that haloarchaeal cells confine phospholipid processing in order to promote midcell elongation. Our findings have important implications for the biogenesis of the cell surface.

Download Full-text

Disease and Carrier Isolates of Neisseria meningitidis Cause G1Cell Cycle Arrest in Human Epithelial Cells

Infection and Immunity ◽

10.1128/iai.00296-16 ◽

2016 ◽

Vol 84 (10) ◽

pp. 2758-2770 ◽

Cited By ~ 8

Author(s):

Michael von Papen ◽

Wilhelm F. Oosthuysen ◽

Jérôme Becam ◽

Heike Claus ◽

Alexandra Schubert-Unkmeir

Keyword(s):

Cell Cycle ◽

Epithelial Cells ◽

Neisseria Meningitidis ◽

Host Cell ◽

Cell Cycle Progression ◽

Kinase Inhibitor ◽

Microbial Pathogens ◽

Meningococcal Infection ◽

Content Type ◽

Cyclin Dependent Kinase Inhibitor

Microbial pathogens have developed several mechanisms to modulate and interfere with host cell cycle progression. In this study, we analyzed the effect of the human pathogenNeisseria meningitidison the cell cycle of epithelial cells. Two pathogenic isolates, as well as two carrier isolates, were tested for their ability to adhere to and invade into the epithelial cell lines Detroit 562 and NP69 and to modulate the cell cycle. We found that all isolates adhered equally well to both Detroit 562 and NP69 cells, whereas the carrier isolates were significantly less invasive. Using propidium iodide staining and 5-ethynyl-2′-deoxyuridine pulse-labeling, we provide evidence that meningococcal infection arrested cells in the G1phase of the cell cycle at 24 h postinfection. In parallel, a significant decrease of cells in the S phase was observed. Interestingly, G1-phase arrest was only induced after infection with live bacteria but not with heat-killed bacteria. By Western blotting we demonstrate that bacterial infection resulted in a decreased protein level of the cell cycle regulator cyclin D1, whereas cyclin E expression levels were increased. Furthermore,N. meningitidisinfection induced an accumulation of the cyclin-dependent kinase inhibitor (CKI) p21WAF1/CIP1that was accompanied by a redistribution of this CKI to the cell nucleus, as shown by immunofluorescence analysis. Moreover, the p27CIP1CKI was redistributed and showed punctate foci in infected cells. In summary, we present data thatN. meningitidiscan interfere with the processes of host cell cycle regulation.

Download Full-text

Rapid Nutritional Remodeling of the Host Cell upon Attachment of Legionella pneumophila

Infection and Immunity ◽

10.1128/iai.01079-13 ◽

2013 ◽

Vol 82 (1) ◽

pp. 72-82 ◽

Cited By ~ 15

Author(s):

William M. Bruckert ◽

Christopher T. Price ◽

Yousef Abu Kwaik

Keyword(s):

Amino Acids ◽

Plasma Membrane ◽

Host Cell ◽

Legionella Pneumophila ◽

Human Monocyte ◽

Bacterial Attachment ◽

Content Type ◽

Cytosolic Side ◽

Novel Strategy ◽

Intracellular Proliferation

ABSTRACTUpon entry ofLegionella pneumophilainto amoebas and macrophages, host-mediated farnesylation of the AnkB effector enables its anchoring to theLegionella-containing vacuole (LCV) membrane. On the LCV, AnkB triggers docking of K48-linked polyubiquitinated proteins that are degraded by the host proteasomes to elevate cellular levels of amino acids needed for intracellular proliferation. Interference with AnkB function triggersL. pneumophilato exhibit a starvation response and differentiate into the nonreplicative phase in response to the basal levels of cellular amino acids that are not sufficient to power intracellular proliferation ofL. pneumophila. Therefore, we have determined whether the biological function of AnkB is temporally and spatially triggered upon bacterial attachment to the host cell to circumvent a counterproductive bacterial differentiation into the nonreplicative phase upon bacterial entry. Here, we show that upon attachment ofL. pneumophilato human monocyte-derived macrophages (hMDMs), the host farnesylation and ubiquitination machineries are recruited by the Dot/Icm system to the plasma membrane exclusively beneath sites of bacterial attachment. Transcription and injection ofankBis triggered by attached extracellular bacteria followed by rapid farnesylation and anchoring of AnkB to the cytosolic side of the plasma membrane beneath bacterial attachment, where K48-linked polyubiquitinated proteins are assembled and degraded by the proteasomes, leading to a rapid rise in the cellular levels of amino acids. Our data represent a novel strategy by an intracellular pathogen that triggers rapid nutritional remodeling of the host cell upon attachment to the plasma membrane, and as a result, a gratuitous surplus of cellular amino acids is generated to support proliferation of the incoming pathogen.

Download Full-text

Benchmarking Various Green Fluorescent Protein Variants in Bacillus subtilis, Streptococcus pneumoniae, and Lactococcus lactis for Live Cell Imaging

Applied and Environmental Microbiology ◽

10.1128/aem.02033-13 ◽

2013 ◽

Vol 79 (20) ◽

pp. 6481-6490 ◽

Cited By ~ 62

Author(s):

Wout Overkamp ◽

Katrin Beilharz ◽

Ruud Detert Oude Weme ◽

Ana Solopova ◽

Harma Karsens ◽

...

Keyword(s):

Bacillus Subtilis ◽

Green Fluorescent Protein ◽

Streptococcus Pneumoniae ◽

Lactococcus Lactis ◽

Cell Biology ◽

Fluorescent Protein ◽

Protein Localization ◽

Experimental Conditions ◽

Content Type ◽

Green Fluorescent

ABSTRACTGreen fluorescent protein (GFP) offers efficient ways of visualizing promoter activity and protein localizationin vivo, and many different variants are currently available to study bacterial cell biology. Which of these variants is best suited for a certain bacterial strain, goal, or experimental condition is not clear. Here, we have designed and constructed two “superfolder” GFPs with codon adaptation specifically forBacillus subtilisandStreptococcus pneumoniaeand have benchmarked them against five other previously available variants of GFP inB. subtilis,S. pneumoniae, andLactococcus lactis, using promoter-gfpfusions. Surprisingly, the best-performing GFP under our experimental conditions inB. subtiliswas the one codon optimized forS. pneumoniaeandvice versa. The data and tools described in this study will be useful for cell biology studies in low-GC-rich Gram-positive bacteria.

Download Full-text

The membrane microenvironment regulates the sequential attachment of bacteria to host cells

10.1101/2020.11.25.397950 ◽

2020 ◽

Author(s):

Xavier Pierrat ◽

Jeremy P.H. Wong ◽

Zainebe Al-Mayyah ◽

Alexandre Persat

Keyword(s):

Cell Surface ◽

Host Cell ◽

Bacterial Adhesion ◽

Bacterial Attachment ◽

Host Cells ◽

Receptor System ◽

Surface Receptors ◽

Inert Surfaces ◽

Mechanical Microenvironment

AbstractPathogen attachment to host tissue is critical in the progress of many infections. Bacteria use adhesion in vivo to promote colonization and regulate the deployment of contact-dependent virulence traits. To specifically target host cells, they decorate themselves with adhesins, proteins that bind to mammalian cell surface receptors. One common assumption is that adhesin-receptor interactions entirely govern bacterial attachment. However, how adhesins engage with their receptors in an in vivo-like context remains unclear, in particular under the influence of a heterogeneous mechanical microenvironment. We here investigate the biophysical processes governing bacterial adhesion to host cells using a tunable adhesin-receptor system. By dynamically visualizing attachment, we found that bacterial adhesion to host cell surface, unlike adhesion to inert surfaces, involves two consecutive steps. Bacteria initially attach to their host without engaging adhesins. This step lasts about one minute during which bacteria can easily detach. We found that at this stage, the glycocalyx, a layer of glycosylated proteins and lipids, shields the host cell by keeping adhesin away from their receptor ligand. In a second step, adhesins engage with their target receptors to strengthen attachment for minutes to hours. The active properties of the membrane, endowed by the actin cytoskeleton, strengthen specific adhesion. Altogether, our results demonstrate that adhesin-ligand binding is not the sole regulator of bacterial adhesion. In fact, the host cell’s mechanical microenvironment relatively strongly mediated host-bacteria physical interactions, thereby playing an essential role in the onset of infection.

Download Full-text