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1.  Antibiotic-specific differences in the response of Staphylococcus aureus to treatment with antimicrobials combined with manuka honey 
Skin infections caused by antibiotic resistant Staphylococcus aureus are a significant health problem worldwide; often associated with high treatment cost and mortality rate. Complex natural products like New Zealand (NZ) manuka honey have been revisited and studied extensively as an alternative to antibiotics due to their potent broad-spectrum antimicrobial activity, and the inability to isolate honey-resistant S. aureus. Previous studies showing synergistic effects between manuka-type honeys and antibiotics have been demonstrated against the growth of one methicillin-resistant S. aureus (MRSA) strain. We have previously demonstrated strong synergistic activity between NZ manuka-type honey and rifampicin against growth and biofilm formation of multiple S. arueus strains. Here, we have expanded our investigation using multiple S. aureus strains and four different antibiotics commonly used to treat S. aureus-related skin infections: rifampicin, oxacillin, gentamicin, and clindamycin. Using checkerboard microdilution and agar diffusion assays with S. aureus strains including clinical isolates and MRSA we demonstrate that manuka-type honey combined with these four antibiotics frequently produces a synergistic effect. In some cases when synergism was not observed, there was a significant enhancement in antibiotic susceptibility. Some strains that were highly resistant to an antibiotic when present alone become sensitive to clinically achievable concentrations when combined with honey. However, not all of the S. aureus strains tested responded in the same way to these combinational treatments. Our findings support the use of NZ manuka-type honeys in clinical treatment against S. aureus-related infections and extend their potential use as an antibiotic adjuvant in combinational therapy. Our data also suggest that manuka-type honeys may not work as antibiotic adjuvants for all strains of S. aureus, and this may help determine the mechanistic processes behind honey synergy.
PMCID: PMC4307217
Medihoney; Staphylococcus aureus; manuka; antibiotic; synergy
2.  Bacterial Stigmergy: An Organising Principle of Multicellular Collective Behaviours of Bacteria 
Scientifica  2015;2015:387342.
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 individuals of the group through the generation of persistent cues in the environment. Interestingly, despite numerous examples 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 examples 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.
PMCID: PMC4306409  PMID: 25653882
3.  Rapid Conversion of Pseudomonas aeruginosa to a Spherical Cell Morphotype Facilitates Tolerance to Carbapenems and Penicillins but Increases Susceptibility to Antimicrobial Peptides 
The Gram-negative human pathogen Pseudomonas aeruginosa tolerates high concentrations of β-lactam antibiotics. Despite inhibiting the growth of the organism, these cell wall-targeting drugs exhibit remarkably little bactericidal activity. However, the mechanisms underlying β-lactam tolerance are currently unclear. Here, we show that P. aeruginosa undergoes a rapid en masse transition from normal rod-shaped cells to viable cell wall-defective spherical cells when treated with β-lactams from the widely used carbapenem and penicillin classes. When the antibiotic is removed, the entire population of spherical cells quickly converts back to the normal bacillary form. Our results demonstrate that these rapid population-wide cell morphotype transitions function as a strategy to survive antibiotic exposure. Taking advantage of these findings, we have developed a novel approach to efficiently kill P. aeruginosa by using carbapenem treatment to induce en masse transition to the spherical cell morphotype and then exploiting the relative fragility and sensitivity of these cells to killing by antimicrobial peptides (AMPs) that are relatively inactive against P. aeruginosa bacillary cells. This approach could broaden the repertoire of antimicrobial compounds used to treat P. aeruginosa and serve as a basis for developing new therapeutic agents to combat bacterial infections.
PMCID: PMC4023726  PMID: 24419348
4.  The biofilm matrix destabilizers, EDTA and DNaseI, enhance the susceptibility of nontypeable Hemophilus influenzae biofilms to treatment with ampicillin and ciprofloxacin 
MicrobiologyOpen  2014;3(4):557-567.
Nontypeable Hemophilus influenzae (NTHi) is a Gram-negative bacterial pathogen that causes chronic biofilm infections of the ears and airways. The biofilm matrix provides structural integrity to the biofilm and protects biofilm cells from antibiotic exposure by reducing penetration of antimicrobial compounds into the biofilm. Extracellular DNA (eDNA) has been found to be a major matrix component of biofilms formed by many species of Gram-positive and Gram-negative bacteria, including NTHi. Interestingly, the cation chelator ethylenediaminetetra-acetic acid (EDTA) has been shown to reduce the matrix strength of biofilms of several bacterial species as well as to have bactericidal activity against various pathogens. EDTA exerts its antimicrobial activity by chelating divalent cations necessary for growth and membrane stability and by destabilizing the matrix thus enhancing the detachment of bacterial cells from the biofilm. In this study, we have explored the role of divalent cations in NTHi biofilm development and stability. We have utilized in vitro static and continuous flow models of biofilm development by NTHi to demonstrate that magnesium cations enhance biofilm formation by NTHi. We found that the divalent cation chelator EDTA is effective at both preventing NTHi biofilm formation and at treating established NTHi biofilms. Furthermore, we found that the matrix destablilizers EDTA and DNaseI increase the susceptibility of NTHi biofilms to ampicillin and ciprofloxacin. Our observations indicate that DNaseI and EDTA enhance the efficacy of antibiotic treatment of NTHi biofilms. These observations may lead to new strategies that will improve the treatment options available to patients with chronic NTHi infections.
PMCID: PMC4287182  PMID: 25044339
Antibiotic; biofilm; cations; eDNA; matrix
5.  Manuka-type honeys can eradicate biofilms produced by Staphylococcus aureus strains with different biofilm-forming abilities 
PeerJ  2014;2:e326.
Chronic wounds are a major global health problem. Their management is difficult and costly, and the development of antibiotic resistance by both planktonic and biofilm-associated bacteria necessitates the use of alternative wound treatments. Honey is now being revisited as an alternative treatment due to its broad-spectrum antibacterial activity and the inability of bacteria to develop resistance to it. Many previous antibacterial studies have used honeys that are not well characterized, even in terms of quantifying the levels of the major antibacterial components present, making it difficult to build an evidence base for the efficacy of honey as an antibiofilm agent in chronic wound treatment. Here we show that a range of well-characterized New Zealand manuka-type honeys, in which two principle antibacterial components, methylglyoxal and hydrogen peroxide, were quantified, can eradicate biofilms of a range of Staphylococcus aureus strains that differ widely in their biofilm-forming abilities. Using crystal violet and viability assays, along with confocal laser scanning imaging, we demonstrate that in all S. aureus strains, including methicillin-resistant strains, the manuka-type honeys showed significantly higher anti-biofilm activity than clover honey and an isotonic sugar solution. We observed higher anti-biofilm activity as the proportion of manuka-derived honey, and thus methylglyoxal, in a honey blend increased. However, methylglyoxal on its own, or with sugar, was not able to effectively eradicate S. aureus biofilms. We also demonstrate that honey was able to penetrate through the biofilm matrix and kill the embedded cells in some cases. As has been reported for antibiotics, sub-inhibitory concentrations of honey improved biofilm formation by some S. aureus strains, however, biofilm cell suspensions recovered after honey treatment did not develop resistance towards manuka-type honeys. New Zealand manuka-type honeys, at the concentrations they can be applied in wound dressings are highly active in both preventing S. aureus biofilm formation and in their eradication, and do not result in bacteria becoming resistant. Methylglyoxal requires other components in manuka-type honeys for this anti-biofilm activity. Our findings support the use of well-defined manuka-type honeys as a topical anti-biofilm treatment for the effective management of wound healing.
PMCID: PMC3970805  PMID: 24711974
Staphylococcus aureus; Biofilm; Honey; Antibacterial; Wounds; Methylglyoxal
6.  Stigmergy 
Bacterial biofilms are complex multicellular communities that are often associated with the emergence of large-scale patterns across the biofilm. How bacteria self-organize to form these structured communities is an area of active research. We have recently determined that the emergence of an intricate network of trails that forms during the twitching motility mediated expansion of Pseudomonas aeruginosa biofilms is attributed to an interconnected furrow system that is forged in the solidified nutrient media by aggregates of cells as they migrate across the media surface. This network acts as a means for self-organization of collective behavior during biofilm expansion as the cells following these vanguard aggregates were preferentially confined within the furrow network resulting in the formation of an intricate network of trails of cells. Here we further explore the process by which the intricate network of trails emerges. We have determined that the formation of the intricate network of furrows is associated with significant remodeling of the sub-stratum underlying the biofilm. The concept of stigmergy has been used to describe a variety of self-organization processes observed in higher organisms and abiotic systems that involve indirect communication via persistent cues in the environment left by individuals that influence the behavior of other individuals of the group at a later point in time. We propose that the concept of stigmergy can also be applied to describe self-organization of bacterial biofilms and can be included in the repertoire of systems used by bacteria to coordinate complex multicellular behaviors.
PMCID: PMC3984292  PMID: 24753789
Self-organisation; twitching motility; biofilms; collective behaviour; Pseudomonas aeruginosa
7.  Atomic force and super-resolution microscopy support a role for LapA as a cell-surface biofilm adhesin of Pseudomonas fluorescens 
Research in microbiology  2012;163(9-10):685-691.
Pseudomonas fluorescence Pf0-1 requires the large repeat protein LapA for stable surface attachment. This study presents direct evidence that LapA is a cell-surface-localized adhesin. Atomic force microscopy (AFM) revealed a significant twofold reduction in adhesion force for mutants lacking the LapA protein on the cell surface compared to the wild-type strain. Deletion of lapG, a gene encoding a periplasmic cysteine protease that functions to release LapA from the cell surface, resulted in a twofold increase in the force of adhesion. Three-dimensional structured illumination microscopy (3D-SIM) revealed the presence of the LapA protein on the cell surface, consistent with its role as an adhesin. The protein is only visualized in the cytoplasm for a mutant of the ABC transporter responsible for translocating LapA to the cell surface. Together, these data highlight the power of combining the use of AFM and 3D-SIM with genetic studies to demonstrate that LapA, a member of a large group of RTX-like repeat proteins, is a cell-surface adhesin.
PMCID: PMC3518552  PMID: 23064158
AFM; Adhesin; Biofilm; Weibull analysis; 3D-SIM
8.  MHJ_0125 is an M42 glutamyl aminopeptidase that moonlights as a multifunctional adhesin on the surface of Mycoplasma hyopneumoniae 
Open Biology  2013;3(4):130017.
Bacterial aminopeptidases play important roles in pathogenesis by providing a source of amino acids from exogenous proteins, destroying host immunological effector peptides and executing posttranslational modification of bacterial and host proteins. We show that MHJ_0125 from the swine respiratory pathogen Mycoplasma hyopneumoniae represents a new member of the M42 class of bacterial aminopeptidases. Despite lacking a recognizable signal sequence, MHJ_0125 is detectable on the cell surface by fluorescence microscopy and LC-MS/MS of (i) biotinylated surface proteins captured by avidin chromatography and (ii) peptides released by mild trypsin shaving. Furthermore, surface-associated glutamyl aminopeptidase activity was detected by incubation of live M. hyopneumoniae cells with the diagnostic substrate H-Glu-AMC. MHJ_0125 moonlights as a multifunctional adhesin, binding to both heparin and plasminogen. Native proteomics and comparative modelling studies suggest MHJ_0125 forms a dodecameric, homopolymeric structure and provide insight into the positions of key residues that are predicted to interact with heparin and plasminogen. MHJ_0125 is the first aminopeptidase shown to both bind plasminogen and facilitate its activation by tissue plasminogen activator. Plasmin cleaves host extracellular matrix proteins and activates matrix metalloproteases, generating peptide substrates for MHJ_0125 and a source of amino acids for growth of M. hyopneumoniae. This unique interaction represents a new paradigm in microbial pathogenesis.
PMCID: PMC3718333  PMID: 23594879
Mycoplasma; aminopeptidase; moonlighting; plasminogen; heparin; homopolymeric complex
9.  A36-dependent Actin Filament Nucleation Promotes Release of Vaccinia Virus 
PLoS Pathogens  2013;9(3):e1003239.
Cell-to-cell transmission of vaccinia virus can be mediated by enveloped virions that remain attached to the outer surface of the cell or those released into the medium. During egress, the outer membrane of the double-enveloped virus fuses with the plasma membrane leaving extracellular virus attached to the cell surface via viral envelope proteins. Here we report that F-actin nucleation by the viral protein A36 promotes the disengagement of virus attachment and release of enveloped virus. Cells infected with the A36YdF virus, which has mutations at two critical tyrosine residues abrogating localised actin nucleation, displayed a 10-fold reduction in virus release. We examined A36YdF infected cells by transmission electron microscopy and observed that during release, virus appeared trapped in small invaginations at the plasma membrane. To further characterise the mechanism by which actin nucleation drives the dissociation of enveloped virus from the cell surface, we examined recombinant viruses by super-resolution microscopy. Fluorescently-tagged A36 was visualised at sub-viral resolution to image cell-virus attachment in mutant and parental backgrounds. We confirmed that A36YdF extracellular virus remained closely associated to the plasma membrane in small membrane pits. Virus-induced actin nucleation reduced the extent of association, thereby promoting the untethering of virus from the cell surface. Virus release can be enhanced via a point mutation in the luminal region of B5 (P189S), another virus envelope protein. We found that the B5P189S mutation led to reduced contact between extracellular virus and the host membrane during release, even in the absence of virus-induced actin nucleation. Our results posit that during release virus is tightly tethered to the host cell through interactions mediated by viral envelope proteins. Untethering of virus into the surrounding extracellular space requires these interactions be relieved, either through the force of actin nucleation or by mutations in luminal proteins that weaken these interactions.
Author Summary
Traversing the plasma membrane of the host cell is a significant challenge for many viruses during the infection cycle, and the efficiency of detachment from the host cell and subsequent release can have implications in pathogenesis. Vaccinia virus exits cells through the loss of an outer membrane but remains attached via viral envelope proteins that mediate adhesion between the cell and virus. Here we report that actin filament nucleation by the viral protein A36 promotes the disengagement of virus attachment. Viruses unable to locally induce actin nucleation displayed significantly reduced release and particles were found trapped in small pits at the plasma membrane. Mutations in luminal viral proteins that disrupt attachment identified an alternative route to virus release, bypassing the requirement for actin nucleation. Our results suggest that untethering virus attachment to the cell surface is a rate-limiting step during exocytic release of vaccinia virus. We have elucidated that the force of actin nucleation is the primary mechanism that operates to relieve these interactions.
PMCID: PMC3605287  PMID: 23555252
10.  Synergism between Medihoney and Rifampicin against Methicillin-Resistant Staphylococcus aureus (MRSA) 
PLoS ONE  2013;8(2):e57679.
Skin and chronic wound infections caused by highly antibiotic resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA) are an increasing and urgent health problem worldwide, particularly with sharp increases in obesity and diabetes. New Zealand manuka honey has potent broad-spectrum antimicrobial activity, has been shown to inhibit the growth of MRSA strains, and bacteria resistant to this honey have not been obtainable in the laboratory. Combinational treatment of chronic wounds with manuka honey and common antibiotics may offer a wide range of advantages including synergistic enhancement of the antibacterial activity, reduction of the effective dose of the antibiotic, and reduction of the risk of antibiotic resistance. The aim of this study was to investigate the effect of Medihoney in combination with the widely used antibiotic rifampicin on S. aureus. Using checkerboard microdilution assays, time-kill curve experiments and agar diffusion assays, we show a synergism between Medihoney and rifampicin against MRSA and clinical isolates of S. aureus. Furthermore, the Medihoney/rifampicin combination stopped the appearance of rifampicin-resistant S. aureus in vitro. Methylglyoxal (MGO), believed to be the major antibacterial compound in manuka honey, did not act synergistically with rifampicin and is therefore not the sole factor responsible for the synergistic effect of manuka honey with rifampicin. Our findings support the idea that a combination of honey and antibiotics may be an effective new antimicrobial therapy for chronic wound infections.
PMCID: PMC3585195  PMID: 23469049
11.  The Effect of New Zealand Kanuka, Manuka and Clover Honeys on Bacterial Growth Dynamics and Cellular Morphology Varies According to the Species 
PLoS ONE  2013;8(2):e55898.
Treatment of chronic wounds is becoming increasingly difficult due to antibiotic resistance. Complex natural products with antimicrobial activity, such as honey, are now under the spotlight as alternative treatments to antibiotics. Several studies have shown honey to have broad-spectrum antibacterial activity at concentrations present in honey dressings, and resistance to honey has not been attainable in the laboratory. However not all honeys are the same and few studies have used honey that is well defined both in geographic and chemical terms. Here we have used a range of concentrations of clover honey and a suite of manuka and kanuka honeys from known geographical locations, and for which the floral source and concentration of methylglyoxal and hydrogen peroxide potential were defined, to determine their effect on growth and cellular morphology of four bacteria: Bacillus subtilis, Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. While the general trend in effectiveness of growth inhibition was manuka>manuka-kanuka blend>kanuka>clover, the honeys had varying and diverse effects on the growth and cellular morphology of each bacterium, and each organism had a unique response profile to these honeys. P. aeruginosa showed a markedly different pattern of growth inhibition to the other three organisms when treated with sub-inhibitory concentrations of honey, being equally sensitive to all honeys, including clover, and the least sensitive to honey overall. While hydrogen peroxide potential contributed to the antibacterial activity of the manuka and kanuka honeys, it was never essential for complete growth inhibition. Cell morphology analysis also showed a varied and diverse set of responses to the honeys that included cell length changes, cell lysis, and alterations to DNA appearance. These changes are likely to reflect the different regulatory circuits of the organisms that are activated by the stress of honey treatment.
PMCID: PMC3572166  PMID: 23418472
12.  The Type II Secretion System and Its Ubiquitous Lipoprotein Substrate, SslE, Are Required for Biofilm Formation and Virulence of Enteropathogenic Escherichia coli 
Infection and Immunity  2012;80(6):2042-2052.
Enteropathogenic Escherichia coli (EPEC) is a major cause of diarrhea in infants in developing countries. We have identified a functional type II secretion system (T2SS) in EPEC that is homologous to the pathway responsible for the secretion of heat-labile enterotoxin by enterotoxigenic E. coli. The wild-type EPEC T2SS was able to secrete a heat-labile enterotoxin reporter, but an isogenic T2SS mutant could not. We showed that the major substrate of the T2SS in EPEC is SslE, an outer membrane lipoprotein (formerly known as YghJ), and that a functional T2SS is essential for biofilm formation by EPEC. T2SS and SslE mutants were arrested at the microcolony stage of biofilm formation, suggesting that the T2SS is involved in the development of mature biofilms and that SslE is a dominant effector of biofilm development. Moreover, the T2SS was required for virulence, as infection of rabbits with a rabbit-specific EPEC strain carrying a mutation in either the T2SS or SslE resulted in significantly reduced intestinal colonization and milder disease.
PMCID: PMC3370571  PMID: 22451516
13.  Extragenic suppressor mutations that restore twitching motility to fimL mutants of Pseudomonas aeruginosa are associated with elevated intracellular cyclic AMP levels 
MicrobiologyOpen  2012;1(4):490-501.
Cyclic AMP (cAMP) is a signaling molecule that is involved in the regulation of multiple virulence systems of the opportunistic pathogen Pseudomonas aeruginosa. The intracellular concentration of cAMP in P. aeruginosa cells is tightly controlled at the levels of cAMP synthesis and degradation through regulation of the activity and/or expression of the adenylate cyclases CyaA and CyaB or the cAMP phosphodiesterase CpdA. Interestingly, mutants of fimL, which usually demonstrate defective twitching motility, frequently revert to a wild-type twitching-motility phenotype presumably via the acquisition of an extragenic suppressor mutation(s). In this study, we have characterized five independent fimL twitching-motility revertants and have determined that all have increased intracellular cAMP levels compared with the parent fimL mutant. Whole-genome sequencing revealed that only one of these fimL revertants has acquired a loss-of-function mutation in cpdA that accounts for the elevated levels of intracellular cAMP. As mutation of cpdA did not account for the restoration of twitching motility observed in the other four fimL revertants, these observations suggest that there is at least another, as yet unidentified, site of extragenic suppressor mutation that can cause phenotypic reversion in fimL mutants and modulation of intracellular cAMP levels of P. aeruginosa.
PMCID: PMC3535393  PMID: 23233287
cAMP; tfp; type IV pili
14.  Subcompartmentalisation of Proteins in the Rhoptries Correlates with Ordered Events of Erythrocyte Invasion by the Blood Stage Malaria Parasite 
PLoS ONE  2012;7(9):e46160.
Host cell infection by apicomplexan parasites plays an essential role in lifecycle progression for these obligate intracellular pathogens. For most species, including the etiological agents of malaria and toxoplasmosis, infection requires active host-cell invasion dependent on formation of a tight junction – the organising interface between parasite and host cell during entry. Formation of this structure is not, however, shared across all Apicomplexa or indeed all parasite lifecycle stages. Here, using an in silico integrative genomic search and endogenous gene-tagging strategy, we sought to characterise proteins that function specifically during junction-dependent invasion, a class of proteins we term invasins to distinguish them from adhesins that function in species specific host-cell recognition. High-definition imaging of tagged Plasmodium falciparum invasins localised proteins to multiple cellular compartments of the blood stage merozoite. This includes several that localise to distinct subcompartments within the rhoptries. While originating from the same organelle, however, each has very different dynamics during invasion. Apical Sushi Protein and Rhoptry Neck protein 2 release early, following the junction, whilst a novel rhoptry protein PFF0645c releases only after invasion is complete. This supports the idea that organisation of proteins within a secretory organelle determines the order and destination of protein secretion and provides a localisation-based classification strategy for predicting invasin function during apicomplexan parasite invasion.
PMCID: PMC3458004  PMID: 23049965
15.  3D-SIM Super Resolution Microscopy Reveals a Bead-Like Arrangement for FtsZ and the Division Machinery: Implications for Triggering Cytokinesis 
PLoS Biology  2012;10(9):e1001389.
Super resolution three-dimensional imaging reveals a new picture of how bacterial cell division proteins localize to the division site, including the formation of dynamic bead-like patterns, and explains how the division ring constricts.
FtsZ is a tubulin-like GTPase that is the major cytoskeletal protein in bacterial cell division. It polymerizes into a ring, called the Z ring, at the division site and acts as a scaffold to recruit other division proteins to this site as well as providing a contractile force for cytokinesis. To understand how FtsZ performs these functions, the in vivo architecture of the Z ring needs to be established, as well as how this structure constricts to enable cytokinesis. Conventional wide-field fluorescence microscopy depicts the Z ring as a continuous structure of uniform density. Here we use a form of super resolution microscopy, known as 3D-structured illumination microscopy (3D-SIM), to examine the architecture of the Z ring in cells of two Gram-positive organisms that have different cell shapes: the rod-shaped Bacillus subtilis and the coccoid Staphylococcus aureus. We show that in both organisms the Z ring is composed of a heterogeneous distribution of FtsZ. In addition, gaps of fluorescence were evident, which suggest that it is a discontinuous structure. Time-lapse studies using an advanced form of fast live 3D-SIM (Blaze) support a model of FtsZ localization within the Z ring that is dynamic and remains distributed in a heterogeneous manner. However, FtsZ dynamics alone do not trigger the constriction of the Z ring to allow cytokinesis. Lastly, we visualize other components of the divisome and show that they also adopt a bead-like localization pattern at the future division site. Our data lead us to propose that FtsZ guides the divisome to adopt a similar localization pattern to ensure Z ring constriction only proceeds following the assembly of a mature divisome.
Author Summary
Because bacterial cells are so small, it is challenging to image the spatial organization of proteins inside them. All the proteins that orchestrate cell division in these organisms localize to the division site prior to division, but it has not so far been possible to obtain a clear highresolution three-dimensional picture of the dynamics of their localization. In this study we use a new type of super resolution microscopy called three-dimensional structured illumination microscopy (3D-SIM) to analyze the localization of proteins involved in cell division in two types of bacteria that have different cell shapes: the rod-shaped Bacillus subtilis and the spherical Staphylococcus aureus. We show that FtsZ, a cytoskeletal protein that serves as a scaffold for the cytokinetic ring, localizes to the division site in a dynamic bead-like pattern, rather than a uniform ring as was previously proposed, in both types of bacteria. Our observations also provide an explanation of how this ring constricts to split a bacterial cell in two and suggests that this spatial organization of division proteins is conserved among bacteria and is crucial for the regulation of this central cellular process.
PMCID: PMC3439403  PMID: 22984350
16.  Expression of a Gi-coupled receptor in the heart causes impaired Ca2+ handling, myofilament injury, and dilated cardiomyopathy 
Increased signaling by Gi-coupled receptors has been implicated in dilated cardiomyopathy. To investigate the mechanisms, we used transgenic mice that develop dilated cardiomyopathy after conditional expression of a cardiac-targeted Gi-coupled receptor (Ro1). Activation of Gi signaling by the Ro1 agonist spiradoline caused decreased cellular cAMP levels and bradycardia in Langendorff-perfused hearts. However, acute termination of Ro1 signaling with the antagonist nor-binaltorphimine did not reverse the Ro1-induced contractile dysfunction, indicating that Ro1 cardiomyopathy was not due to acute effects of receptor signaling. Early after initiation of Ro1 expression, there was a 40% reduction in the abundance of the sarcoplasmic reticulum Ca2+-ATPase (P < 0.05); thereafter, there was progressive impairment of both Ca2+ handling and force development assessed with ventricular trabeculae. Six weeks after initiation of Ro1 expression, systolic Ca2+ concentration was reduced to 0.61 ± 0.08 vs. 0.91 ± 0.07 μM for control (n = 6–8; P < 0.05), diastolic Ca2+ concentration was elevated to 0.41 ± 0.07 vs. 0.23 ± 0.06 μM for control (n = 6–8; P < 0.01), and the decline phase of the Ca2+ transient (time from peak to 50% decline) was slowed to 0.25 ± 0.02 s vs. 0.13 ± 0.02 s for control (n = 6–8; P < 0.01). Early after initiation of Ro1 expression, there was a ninefold elevation of matrix metalloprotein-ase-2 (P < 0.01), which is known to cause myofilament injury. Consistent with this, 6 wk after initiation of Ro1 expression, Ca2+-saturated myofilament force in skinned trabeculae was reduced to 21 ± 2 vs. 38 ± 0.1 mN/mm2 for controls (n = 3; P < 0.01). Furthermore, electron micrographs revealed extensive myofilament damage. These findings may have implications for some forms of human heart failure in which increased activity of Gi-coupled receptors leads to impaired Ca2+ handling and myofilament injury, contributing to impaired ventricular pump function and heart failure.
PMCID: PMC3372085  PMID: 17965283
matrix metalloproteinase-2; sarco(endo)plasmic reticulum Ca2+-ATPase; contraction; κ-opioid receptor; conditional expression
17.  Spatial Localisation of Actin Filaments across Developmental Stages of the Malaria Parasite 
PLoS ONE  2012;7(2):e32188.
Actin dynamics have been implicated in a variety of developmental processes during the malaria parasite lifecycle. Parasite motility, in particular, is thought to critically depend on an actomyosin motor located in the outer pellicle of the parasite cell. Efforts to understand the diverse roles actin plays have, however, been hampered by an inability to detect microfilaments under native conditions. To visualise the spatial dynamics of actin we generated a parasite-specific actin antibody that shows preferential recognition of filamentous actin and applied this tool to different lifecycle stages (merozoites, sporozoites and ookinetes) of the human and mouse malaria parasite species Plasmodium falciparum and P. berghei along with tachyzoites from the related apicomplexan parasite Toxoplasma gondii. Actin filament distribution was found associated with three core compartments: the nuclear periphery, pellicular membranes of motile or invasive parasite forms and in a ring-like distribution at the tight junction during merozoite invasion of erythrocytes in both human and mouse malaria parasites. Localisation at the nuclear periphery is consistent with an emerging role of actin in facilitating parasite gene regulation. During invasion, we show that the actin ring at the parasite-host cell tight junction is dependent on dynamic filament turnover. Super-resolution imaging places this ring posterior to, and not concentric with, the junction marker rhoptry neck protein 4. This implies motor force relies on the engagement of dynamic microfilaments at zones of traction, though not necessarily directly through receptor-ligand interactions at sites of adhesion during invasion. Combined, these observations extend current understanding of the diverse roles actin plays in malaria parasite development and apicomplexan cell motility, in particular refining understanding on the linkage of the internal parasite gliding motor with the extra-cellular milieu.
PMCID: PMC3289632  PMID: 22389687
18.  Tracking Glideosome-Associated Protein 50 Reveals the Development and Organization of the Inner Membrane Complex of Plasmodium falciparum ▿ † 
Eukaryotic Cell  2011;10(4):556-564.
The most deadly of the human malaria parasites, Plasmodium falciparum, has different stages specialized for invasion of hepatocytes, erythrocytes, and the mosquito gut wall. In each case, host cell invasion is powered by an actin-myosin motor complex that is linked to an inner membrane complex (IMC) via a membrane anchor called the glideosome-associated protein 50 (PfGAP50). We generated P. falciparum transfectants expressing green fluorescent protein (GFP) chimeras of PfGAP50 (PfGAP50-GFP). Using immunoprecipitation and fluorescence photobleaching, we show that C-terminally tagged PfGAP50-GFP can form a complex with endogenous copies of the linker protein PfGAP45 and the myosin A tail domain-interacting protein (MTIP). Full-length PfGAP50-GFP is located in the endoplasmic reticulum in early-stage parasites and then redistributes to apical caps during the formation of daughter merozoites. In the final stage of schizogony, the PfGAP50-GFP profile extends further around the merozoite surface. Three-dimensional (3D) structured illumination microscopy reveals the early-stage IMC as a doubly punctured flat ellipsoid that separates to form claw-shaped apposed structures. A GFP fusion of PfGAP50 lacking the C-terminal membrane anchor is misdirected to the parasitophorous vacuole. Replacement of the acid phosphatase homology domain of PfGAP50 with GFP appears to allow correct trafficking of the chimera but confers a growth disadvantage.
PMCID: PMC3127638  PMID: 21239623
19.  Pseudomonas aeruginosa AES-1 Exhibits Increased Virulence Gene Expression during Chronic Infection of Cystic Fibrosis Lung 
PLoS ONE  2011;6(9):e24526.
Pseudomonas aeruginosa, the leading cause of morbidity and mortality in people with cystic fibrosis (CF), adapts for survival in the CF lung through both mutation and gene expression changes. Frequent clonal strains such as the Australian Epidemic Strain-1 (AES-1), have increased ability to establish infection in the CF lung and to superimpose and replace infrequent clonal strains. Little is known about the factors underpinning these properties. Analysis has been hampered by lack of expression array templates containing CF-strain specific genes. We sequenced the genome of an acute infection AES-1 isolate from a CF infant (AES-1R) and constructed a non-redundant micro-array (PANarray) comprising AES-1R and seven other sequenced P. aeruginosa genomes. The unclosed AES-1R genome comprised 6.254Mbp and contained 6957 putative genes, including 338 not found in the other seven genomes. The PANarray contained 12,543 gene probe spots; comprising 12,147 P. aeruginosa gene probes, 326 quality-control probes and 70 probes for non-P. aeruginosa genes, including phage and plant genes. We grew AES-1R and its isogenic pair AES-1M, taken from the same patient 10.5 years later and not eradicated in the intervening period, in our validated artificial sputum medium (ASMDM) and used the PANarray to compare gene expression of both in duplicate. 675 genes were differentially expressed between the isogenic pairs, including upregulation of alginate, biofilm, persistence genes and virulence-related genes such as dihydroorotase, uridylate kinase and cardiolipin synthase, in AES-1M. Non-PAO1 genes upregulated in AES-1M included pathogenesis-related (PAGI-5) genes present in strains PACS2 and PA7, and numerous phage genes. Elucidation of these genes' roles could lead to targeted treatment strategies for chronically infected CF patients.
PMCID: PMC3174184  PMID: 21935417
20.  A Genetic Switch to Hypervirulence Reduces Colonization Phenotypes of the Globally Disseminated Group A Streptococcus M1T1 Clone 
The recent resurgence of invasive group A streptococcal disease has been paralleled by the emergence of the M1T1 clone. Recently, invasive disease initiation to has been linked to mutations in the covR/S two-compnent regulator. Here we investigate if a fitness cost is associated with covS mutation that counterbalances hypervirulence.
Wild-type M1T1 GAS and an isogenic covS mutant derived from animal passage were compared for adherence to human laryngeal epithelial cells, keratinocytes or fibronectin, biofilm formation, and binding to intact mouse skin. Targeted mutagenesis of capsule expression from both strains was performed for analysis of its unique contribution to the observed phenotypes.
The covS mutant bacteria showed reduced capacity to bind to epithelial cell layers as a consequence of increased capsule expression. The covS mutant strain also had reduced capacity to bind fibronectin and to form biofilms on plastic and epithelial cell layers. A defect in skin adherence of the covS mutant strain was demonstrated in a murine model.
Reduced colonization capacity provides a potential explanation as to why the covS mutation conferring hypervirulence has not become fixed in the globally-disseminated M1T1 GAS clone, but rather may arise anew under innate immune selection in individual patients.
PMCID: PMC2880657  PMID: 20507231
23.  A diagnostic PCR assay for the detection of an Australian epidemic strain of Pseudomonas aeruginosa 
Chronic lung infection with the bacterium Pseudomonas aeruginosa is one of the hallmarks of cystic fibrosis (CF) and is associated with worsening lung function, increased hospitalisation and reduced life expectancy. A virulent clonal strain of P. aeruginosa (Australian epidemic strain I; AES-I) has been found to be widespread in CF patients in eastern Australia.
Suppression subtractive hybridization (SSH) was employed to identify genetic sequences that are present in the AES-I strain but absent from the sequenced reference strain PAO1. We used PCR to evaluate the distribution of several of the AES-I loci amongst a collection of 188 P. aeruginosa isolates which was comprised of 35 AES-I isolates (as determined by PFGE), 78 non-AES-I CF isolates including other epidemic CF strains as well as 69 P. aeruginosa isolates from other clinical and environmental sources.
We have identified a unique AES-I genetic locus that is present in all 35 AES-I isolates tested and not present in any of the other 153 P. aeruginosa strains examined. We have used this unique AES-I locus to develop a diagnostic PCR and a real-time PCR assay to detect the presence of P. aeruginosa and AES-I in patient sputum samples.
We have developed diagnostic PCR assays that are 100% sensitive and 100% specific for the P. aeruginosa strain AES-I. We have also shown that Whatman FTA® Elute cards may be used with PCR-based assays to rapidly detect the presence of P. aeruginosa strains in CF sputum.
PMCID: PMC2912777  PMID: 20637114
24.  Twitching Motility Is Essential for Virulence in Dichelobacter nodosus▿ †  
Journal of Bacteriology  2008;190(9):3323-3335.
Type IV fimbriae are essential virulence factors of Dichelobacter nodosus, the principal causative agent of ovine foot rot. The fimA fimbrial subunit gene is required for virulence, but fimA mutants exhibit several phenotypic changes and it is not certain if the effects on virulence result from the loss of type IV fimbria-mediated twitching motility, cell adherence, or reduced protease secretion. We showed that mutation of either the pilT or pilU gene eliminated the ability to carry out twitching motility. However, the pilT mutants displayed decreased adhesion to epithelial cells and reduced protease secretion, whereas the pilU mutants had wild-type levels of extracellular protease secretion and adherence. These data provided evidence that PilT is required for the type IV fimbria-dependent protease secretion pathway in D. nodosus. It was postulated that sufficient fimbrial retraction must occur in the pilU mutants to allow protease secretion, but not twitching motility, to take place. Although no cell movement was detected in a pilU mutant of D. nodosus, aberrant motion was detected in an equivalent mutant of Pseudomonas aeruginosa. These observations explain how in D. nodosus protease secretion can occur in a pilU mutant but not in a pilT mutant. In addition, virulence studies with sheep showed that both the pilT and pilU mutants were avirulent, providing evidence that mutation of the type IV fimbrial system affects virulence by eliminating twitching motility, not by altering cell adherence or protease secretion.
PMCID: PMC2347375  PMID: 18310333
25.  α1-Adrenergic receptors prevent a maladaptive cardiac response to pressure overload 
Journal of Clinical Investigation  2006;116(4):1005-1015.
An α1-adrenergic receptor (α1-AR) antagonist increased heart failure in the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT), but it is unknown whether this adverse result was due to α1-AR inhibition or a nonspecific drug effect. We studied cardiac pressure overload in mice with double KO of the 2 main α1-AR subtypes in the heart, α1A (Adra1a) and α1B (Adra1b). At 2 weeks after transverse aortic constriction (TAC), KO mouse survival was only 60% of WT, and surviving KO mice had lower ejection fractions and larger end-diastolic volumes than WT mice. Mechanistically, final heart weight and myocyte cross-sectional area were the same after TAC in KO and WT mice. However, KO hearts after TAC had increased interstitial fibrosis, increased apoptosis, and failed induction of the fetal hypertrophic genes. Before TAC, isolated KO myocytes were more susceptible to apoptosis after oxidative and β-AR stimulation, and β-ARs were desensitized. Thus, α1-AR deletion worsens dilated cardiomyopathy after pressure overload, by multiple mechanisms, indicating that α1-signaling is required for cardiac adaptation. These results suggest that the adverse cardiac effects of α1-antagonists in clinical trials are due to loss of α1-signaling in myocytes, emphasizing concern about clinical use of α1-antagonists, and point to a revised perspective on sympathetic activation in heart failure.
PMCID: PMC1421341  PMID: 16585965

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