ORCID Profile
0000-0001-8895-3444
Current Organisation
Virginia Tech
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Publisher: Proceedings of the National Academy of Sciences
Date: 24-06-2013
Abstract: Twitching motility-mediated biofilm expansion is a complex, multicellular behavior that enables the active colonization of surfaces by many species of bacteria. In this study we have explored the emergence of intricate network patterns of interconnected trails that form in actively expanding biofilms of Pseudomonas aeruginosa . We have used high-resolution, phase-contrast time-lapse microscopy and developed sophisticated computer vision algorithms to track and analyze in idual cell movements during expansion of P. aeruginosa biofilms. We have also used atomic force microscopy to examine the topography of the substrate underneath the expanding biofilm. Our analyses reveal that at the leading edge of the biofilm, highly coherent groups of bacteria migrate across the surface of the semisolid media and in doing so create furrows along which following cells preferentially migrate. This leads to the emergence of a network of trails that guide mass transit toward the leading edges of the biofilm. We have also determined that extracellular DNA (eDNA) facilitates efficient traffic flow throughout the furrow network by maintaining coherent cell alignments, thereby avoiding traffic jams and ensuring an efficient supply of cells to the migrating front. Our analyses reveal that eDNA also coordinates the movements of cells in the leading edge vanguard rafts and is required for the assembly of cells into the “bulldozer” aggregates that forge the interconnecting furrows. Our observations have revealed that large-scale self-organization of cells in actively expanding biofilms of P. aeruginosa occurs through construction of an intricate network of furrows that is facilitated by eDNA.
Publisher: Springer Science and Business Media LLC
Date: 21-08-2020
DOI: 10.1186/S12903-020-01217-0
Abstract: Dental plaque biofilms are the causative agents of caries, gingivitis and periodontitis. Both mechanical and chemical strategies are used in routine oral hygiene strategies to reduce plaque build-up. If allowed to mature biofilms can create anoxic microenvironments leading to communities which harbor pathogenic Gram-negative anaerobes. When subjected to high velocity fluid jets and sprays biofilms can be fluidized which disrupts the biofilm structure and allows the more efficient delivery of antimicrobial agents. To investigate how such jets may disrupt anoxic niches in the biofilm, we used planar optodes to measure the dissolved oxygen (DO) concentration at the base of in-vitro biofilms grown from human saliva and dental plaque. These biofilms were subject to “shooting” treatments with a commercial high velocity microspray (HVM) device. HVM treatment resulted in removal of much of the biofilm and a concurrent rapid shift from anoxic to oxic conditions at the base of the surrounding biofilm. We also assessed the impact of HVM treatment on the microbial community by tracking 7 target species by qPCR. There was a general reduction in copy numbers of the universal 16S RNA by approximately 95%, and changes of in idual species in the target region ranged from approximately 1 to 4 log reductions. We concluded that high velocity microsprays removed a sufficient amount of biofilm to disrupt the anoxic region at the biofilm-surface interface.
Publisher: American Society for Microbiology
Date: 26-10-2023
DOI: 10.1128/JB.00238-23
Publisher: American Society for Microbiology
Date: 27-08-2019
Abstract: Bacteria adapt to infections by evolving variants that are more fit and persistent. These recalcitrant variants are typically observed in chronic infections. However, it is unclear when and why these variants evolve. To address these questions, we used a porcine chronic wound model to study the evolutionary dynamics of Pseudomonas aeruginosa in a mixed-strain infection. We isolated hyperbiofilm variants that persisted early in the infection. Interstrain interactions were also observed, where adapted variants acquired CRISPR-mediated immunity to phages. We show that when initiating infection, P. aeruginosa experiences strong positive selection for hyperbiofilm phenotypes produced by mutants of a single chemosensory system, the Wsp pathway. We predict that hyperbiofilm variants are early adaptations to infection and that interstrain interactions may influence bacterial burden and infection outcomes.
Publisher: Cold Spring Harbor Laboratory
Date: 02-02-2021
DOI: 10.1101/2021.02.01.429245
Abstract: Interactions between bacteria, their close competitors, and viral parasites are common in infections but understanding of these eco-evolutionary dynamics is limited. Most ex les of adaptations caused by phage lysogeny are through the acquisition of new genes. However, integrated prophages can also insert into functional genes and impart a fitness benefit by disrupting their expression, a process called active lysogeny. Here, we show that active lysogeny can fuel rapid, parallel adaptations in establishing a chronic infection. These recombination events repeatedly disrupted genes encoding global regulators, leading to increased cyclic-di-GMP levels and elevated biofilm production. The implications of prophage-mediated adaptation are broad, as even transient members of microbial communities can alter the course of evolution and generate persistent phenotypes associated with poor clinical outcomes. Bacteriophage act as genetic regulators that are key to establishing chronic infections and are rapidly shared among co-infecting strains.
Publisher: Informa UK Limited
Date: 09-11-2013
DOI: 10.4161/CIB.27331
Publisher: Proceedings of the National Academy of Sciences
Date: 25-11-2019
Abstract: Most chronic and recurrent bacterial infections are the result of biofilms. Extracellular DNA (eDNA) is a ubiquitous and pivotal structural component of biofilms that protects the resident bacteria from the host immune system and antimicrobial agents. It is of the highest priority to characterize the structure of the eDNA to understand the development of bacterial biofilm communities. Here, we employed the prototypic Holliday junction-specific (HJ) DNA-binding protein RuvA and demonstrated that eDNA within biofilms formed by 3 human pathogens, uropathogenic Escherichia coli , nontypeable Haemophilus influenzae , and Staphylococcus epidermidis was structurally related to HJ recombination intermediates. We further demonstrated that this HJ-like structure was critical to the structural and mechanical integrity of the bacterial biofilm matrix.
Publisher: Springer Science and Business Media LLC
Date: 02-02-2023
DOI: 10.1038/S41522-023-00375-7
Abstract: Pel exopolysaccharide biosynthetic loci are phylogenetically widespread biofilm matrix determinants in bacteria. In Pseudomonas aeruginosa , Pel is crucial for cell-to-cell interactions and reducing susceptibility to antibiotic and mucolytic treatments. While genes encoding glycoside hydrolases have long been linked to biofilm exopolysaccharide biosynthesis, their physiological role in biofilm development is unclear. Here we demonstrate that the glycoside hydrolase activity of P. aeruginosa PelA decreases adherent biofilm biomass and is responsible for generating the low molecular weight secreted form of the Pel exopolysaccharide. We show that the generation of secreted Pel contributes to the biomechanical properties of the biofilm and decreases the virulence of P. aeruginosa in Caenorhabditis elegans and Drosophila melanogaster . Our results reveal that glycoside hydrolases found in exopolysaccharide biosynthetic systems can help shape the soft matter attributes of a biofilm and propose that secreted matrix components be referred to as matrix associated to better reflect their influence.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 07-2021
Publisher: Cold Spring Harbor Laboratory
Date: 17-01-2023
DOI: 10.1101/2023.01.15.524085
Abstract: Bacterial infections are often polymicrobial. Pseudomonas aeruginosa and Staphylococcus aureus cause chronic co-infections, which are more problematic than mono-species infections. We found that the production of S. aureus membrane-bound pigment staphyloxanthin (STX), was induced by the P. aeruginosa exoproduct, 2-heptyl-4-hydroxyquinoline N-oxide (HQNO). The induction phenotype was conserved in P. aeruginosa and S. aureus clinical isolates examined. When subjected to hydrogen peroxide or human neutrophils, P. aeruginosa survival was significantly higher when mixed with wild-type (WT) S. aureus , compared to a mutant deficient in STX production or P. aeruginosa alone. In a murine wound model, co-infection with WT S. aureus , but not the STX-deficient mutant, enhanced P. aeruginosa burden and disease compared to mono-infection. In conclusion, we discovered a novel role for P. aeruginosa HQNO mediating polymicrobial interactions with S. aureus by inducing STX production, which consequently promotes resistance of both pathogens to innate immune effectors. These results further our understanding of how different bacterial species cooperatively cause co-infections.
Publisher: Frontiers Media SA
Date: 05-11-2021
DOI: 10.3389/FCIMB.2021.784388
Abstract: Oral diseases are one of the most common pathologies affecting human health. These diseases are typically associated with dental plaque-biofilms, through either build-up of the biofilm or dysbiosis of the microbial community. Arginine can disrupt dental plaque-biofilms, and maintain plaque homeostasis, making it an ideal therapeutic to combat the development of oral disease. Despite our understanding of the actions of arginine towards dental plaque-biofilms, it is still unclear how or if arginine effects the mechanical integrity of the dental plaque-biofilm. Here we adapted a rotating-disc rheometry assay, a method used to quantify marine biofilm fouling, to study how arginine treatment of Streptococcus gordonii biofilms influences biofilm detachment from surfaces. We demonstrate that the assay is highly sensitive at quantifying the presence of biofilm and the detachment or rearrangement of the biofilm structure as a function of shear stress. We demonstrate that arginine treatment leads to earlier detachment of the biofilm, indicating that arginine treatment weakens the biofilm, making it more susceptible to removal by shear stresses. Finally, we demonstrate that the biofilm disrupting affect is specific to arginine, and not a general property of amino acids, as S. gordonii biofilms treated with either glycine or lysine had mechanical properties similar to untreated biofilms. Our results add to the understanding that arginine targets biofilms by multifaceted mechanisms, both metabolic and physical, further promoting the potential of arginine as an active compound in dentifrices to maintain oral health.
Publisher: Frontiers Media SA
Date: 23-01-2016
Publisher: MyJove Corporation
Date: 08-06-2022
DOI: 10.3791/63773
Abstract: Neutrophils are the first line of defense deployed by the immune system during microbial infection. In vivo, neutrophils are recruited to the site of infection where they use processes such as phagocytosis, production of reactive oxygen and nitrogen species (ROS, RNS, respectively), NETosis (neutrophil extracellular trap), and degranulation to kill microbes and resolve the infection. Interactions between neutrophils and planktonic microbes have been extensively studied. There have been emerging interests in studying infections caused by biofilms in recent years. Biofilms exhibit properties, including tolerance to killing by neutrophils, distinct from their planktonic-grown counterparts. With the successful establishment of both in vitro and in vivo biofilm models, interactions between these microbial communities with different immune cells can now be investigated. Here, techniques that use a combination of traditional biofilm models and well-established neutrophil activity assays are tailored specifically to study neutrophil and biofilm interactions. Wide-field fluorescence microscopy is used to monitor the localization of neutrophils in biofilms. These biofilms are grown in static conditions, followed by the addition of neutrophils derived from human peripheral blood. The s les are stained with appropriate dyes prior to visualization under the microscope. Additionally, the production of ROS, which is one of the many neutrophil responses against pathogens, is quantified in the presence of a biofilm. The addition of immune cells to this established system will expand the understanding of host-pathogen interactions while ensuring the use of standardized and optimized conditions to measure these processes accurately.
Publisher: American Physical Society (APS)
Date: 04-10-2017
Publisher: Hindawi Limited
Date: 2015
DOI: 10.1155/2015/387342
Abstract: The self-organisation of collective behaviours often manifests as dramatic patterns of emergent large-scale order. This is true for relatively “simple” entities such as microbial communities and robot “swarms,” through to more complex self-organised systems such as those displayed by social insects, migrating herds, and many human activities. The principle of stigmergy describes those self-organised phenomena that emerge as a consequence of indirect communication between in iduals of the group through the generation of persistent cues in the environment. Interestingly, despite numerous ex les of multicellular behaviours of bacteria, the principle of stigmergy has yet to become an accepted theoretical framework that describes how bacterial collectives self-organise. Here we review some ex les of multicellular bacterial behaviours in the context of stigmergy with the aim of bringing this powerful and elegant self-organisation principle to the attention of the microbial research community.
Publisher: Cold Spring Harbor Laboratory
Date: 29-10-2018
DOI: 10.1101/456186
Publisher: Elsevier BV
Date: 12-2020
Publisher: Springer Science and Business Media LLC
Date: 26-06-2018
DOI: 10.1038/S41598-018-28009-5
Abstract: Pseudomonas aeruginosa evolves during chronic pulmonary infections of cystic fibrosis (CF) patients, forming pathoadapted variants that are persistent. Mucoid and rugose small-colony variants (RSCVs) are typically isolated from sputum of CF patients. These variants overproduce exopolysaccharides in the biofilm extracellular polymeric substance (EPS). Currently, changes to the biophysical properties of RSCV and mucoid biofilms due to variations in EPS are not well understood. This knowledge may reveal how lung infections resist host clearance mechanisms. Here, we used mechanical indentation and shear rheometry to analyse the viscoelasticity of RSCV and mucoid colony-biofilms compared to their isogenic parent at 2-, 4-, and 6-d. While the viscoelasticity of parental colony-biofilms underwent fluctuating temporal changes, in contrast, RSCV and mucoid colony-biofilms showed a gradual progression to more elastic-solid behaviour. Theoretical indices of mucociliary and cough clearance predict that mature 6-d parental and RSCV biofilms may show reduced cough clearance from the lung, while early mucoid biofilms may show reduced clearance by both mechanisms. We propose that viscoelasticity be considered a virulence property of biofilms.
Publisher: Springer Science and Business Media LLC
Date: 03-03-2021
DOI: 10.1038/S41598-021-84525-X
Abstract: Mycobacterium abscessus is emerging as a cause of recalcitrant chronic pulmonary infections, particularly in people with cystic fibrosis (CF). Biofilm formation has been implicated in the pathology of this organism, however the role of biofilm formation in infection is unclear. Two colony-variants of M. abscessus are routinely isolated from CF s les, smooth ( Ma Sm ) and rough ( Ma Rg ). These two variants display distinct colony morphologies due to the presence ( Ma Sm ) or absence ( Ma Rg ) of cell wall glycopeptidolipids (GPLs). We hypothesized that Ma Sm and Ma Rg variant biofilms might have different mechanical properties. To test this hypothesis, we performed uniaxial mechanical indentation, and shear rheometry on Ma Sm and Ma Rg colony-biofilms. We identified that Ma Rg biofilms were significantly stiffer than Ma Sm under a normal force, while Ma Sm biofilms were more pliant compared to Ma Rg , under both normal and shear forces. Furthermore, using theoretical indices of mucociliary and cough clearance, we identified that M. abscessus biofilms may be more resistant to mechanical forms of clearance from the lung, compared to another common pulmonary pathogen, Pseudomonas aeruginosa. Thus, the mechanical properties of M. abscessus biofilms may contribute to the persistent nature of pulmonary infections caused by this organism.
Publisher: American Society for Microbiology
Date: 17-05-2022
DOI: 10.1128/JB.00086-22
Abstract: Bacterial biofilms are a significant concern in many aspects of life, including chronic infections of airways, wounds, and indwelling medical devices biofouling of industrial surfaces relevant for food production and marine surfaces and nosocomial infections. The effects of understanding surface adhesion could impact many areas of life.
Publisher: Cold Spring Harbor Laboratory
Date: 15-03-2021
DOI: 10.1101/2021.03.15.435500
Abstract: Oral diseases are one of the most common pathologies affecting human health. These diseases are typically associated with dental plaque-biofilms, through either build-up of the biofilm or dysbiosis of the microbial community. Arginine can disrupt dental plaque-biofilms, and maintain plaque homeostasis, making it an ideal therapeutic to combat the development of oral disease. Despite our understanding of the actions of arginine towards dental plaque-biofilms, it is still unclear how or if arginine effects the mechanical integrity of the dental plaque-biofilm. Here we adapted a rotating-disc rheometry assay, which is routinely used in marine microbial ecology, to study how arginine treatment of Streptococcus gordonii biofilms influences biofilm detachment from surfaces. We demonstrate that the assay is highly sensitive at quantifying the presence of biofilm and the detachment or rearrangement of the biofilm structure as a function of shear stress. We demonstrate that arginine treatment leads to earlier detachment of the biofilm, indicating that arginine treatment weakens the biofilm, making it more suspectable to removal by shear stresses. Our results add to the understanding that arginine targets biofilms by multifaceted mechanisms, both metabolic and physical, further promoting the potential of arginine as an active compound in dentifrices to maintain oral health.
Publisher: American Society for Microbiology
Date: 14-02-2023
DOI: 10.1128/SPECTRUM.03351-22
Abstract: Mechanical removal of dental plaque is augmented with therapeutic compounds to promote oral health. A dentifrice containing the ingredients zinc and arginine has shown efficacy at reducing dental plaque both in vitro and in vivo .
Publisher: Cold Spring Harbor Laboratory
Date: 20-10-2020
DOI: 10.1101/2020.10.20.347252
Abstract: Mycobacterium abscessus is emerging as a cause of recalcitrant chronic pulmonary infections, particularly in people with cystic fibrosis (CF). Biofilm formation has been implicated in the pathology of this organism, however the role of biofilm formation in infection is unclear. Two colony-variants of M. abscessus are routinely isolated from CF s les, smooth ( Ma Sm ) and rough ( Ma Rg ). These two variants display distinct colony morphologies due to the presence ( Ma Sm ) or absence ( Ma Rg ) of cell wall glycopeptidolipids (GPLs). We hypothesized that Ma Sm and Ma Rg variant biofilms might have different biophysical and mechanical properties, including stiffness, viscosity and elasticity. To test this hypothesis, we performed uniaxial mechanical indentation, and shear rheometry on Ma Sm and Ma Rg colony-biofilms. We identified that Ma Rg biofilms were significantly stiffer than Ma Sm under a normal force, while Ma Sm biofilms were more pliant compared to Ma Rg , under both normal and shear forces. Furthermore, using theoretical indices of mucociliary and cough clearence, we identified that M. abscessus biofilms may be more resistant to mechanical forms of clearance from the lung, compared to other common pulmonary pathogens, such as P. aeruginosa. Thus, the mechanical properties of M. abscessus biofilms may contribute to the persistent nature of pulmonary infections caused by this organism.
Publisher: Springer Science and Business Media LLC
Date: 14-04-2016
DOI: 10.1038/NCOMMS11220
Abstract: Many bacteria produce extracellular and surface-associated components such as membrane vesicles (MVs), extracellular DNA and moonlighting cytosolic proteins for which the biogenesis and export pathways are not fully understood. Here we show that the explosive cell lysis of a sub-population of cells accounts for the liberation of cytosolic content in Pseudomonas aeruginosa biofilms. Super-resolution microscopy reveals that explosive cell lysis also produces shattered membrane fragments that rapidly form MVs. A prophage endolysin encoded within the R- and F-pyocin gene cluster is essential for explosive cell lysis. Endolysin-deficient mutants are defective in MV production and biofilm development, consistent with a crucial role in the biogenesis of MVs and liberation of extracellular DNA and other biofilm matrix components. Our findings reveal that explosive cell lysis, mediated through the activity of a cryptic prophage endolysin, acts as a mechanism for the production of bacterial MVs.
Publisher: American Society for Microbiology
Date: 17-05-2022
DOI: 10.1128/JB.00076-22
Abstract: Pseudomonas aeruginosa and Staphylococcus aureus are two important opportunistic human pathogens commonly coisolated from clinical s les. However, P. aeruginosa can utilize various mechanisms to antagonize S. aureus in vitro .
Publisher: Springer Science and Business Media LLC
Date: 26-05-2016
DOI: 10.1038/SREP26005
Abstract: Surface translocation by the soil bacterium Myxococcus xanthus is a complex multicellular phenomenon that entails two motility systems. However, the mechanisms by which the activities of in idual cells are coordinated to manifest this collective behaviour are currently unclear. Here we have developed a novel assay that enables detailed microscopic examination of M. xanthus motility at the interstitial interface between solidified nutrient medium and a glass coverslip. Under these conditions, M. xanthus motility is characterised by extensive micro-morphological patterning that is considerably more elaborate than occurs at an air-surface interface. We have found that during motility on solidified nutrient medium, M. xanthus forges an interconnected furrow network that is lined with an extracellular matrix comprised of exopolysaccharides, extracellular lipids, membrane vesicles and an unidentified slime. Our observations have revealed that M. xanthus motility on solidified nutrient medium is a stigmergic phenomenon in which multi-cellular collective behaviours are co-ordinated through trail-following that is guided by physical furrows and extracellular matrix materials.
Publisher: Elsevier BV
Date: 11-2021
No related grants have been discovered for Erin Gloag.