Angela Nobbs | University of Bristol (original) (raw)

Papers by Angela Nobbs

Microbes and infection / Institut Pasteur, Jan 21, 2015

Different sites within the oropharynx harbour unique microbial communities. Co-evolution of micro... more Different sites within the oropharynx harbour unique microbial communities. Co-evolution of microbes and host has resulted in complex interkingdom circuitries. Metabolic signalling is crucial to these processes, and novel microbial communication factors are progressively being discovered. Resolving interkingdom networks will lead to better understanding of oral health or disease aetiology.

Infection, Genetics and Evolution, 2014

Bacteria within the genus Streptococcus have evolved to become exquisitely adapted to the coloniz... more Bacteria within the genus Streptococcus have evolved to become exquisitely adapted to the colonization of humans and other animals. These bacteria predominantly live in harmony with their hosts, but all have capacity to cause disease should prevailing conditions allow. Streptococci express a myriad of colonization and virulence attributes that promote their survival at a variety of ecological sites. Many of these factors are surface-expressed adhesins that exhibit conservation at structural or functional levels across the genus. This reflects the importance of adherence interactions with a multitude of host substrata, such as epithelia or extracellular matrix components, to streptococcal survival. Other important factors are more restricted in their distribution, often conferring pathogenic capabilities associated with immune evasion or host tissue destruction. Evidence suggests that dissemination of these streptococcal attributes has frequently been driven by the movement of genetic material via lateral gene transfer, reflecting ecological pressures. Such recombination events have simultaneously facilitated extensive diversification, resulting in distinct tropisms at the species- or strain- level. These generic determinants offer significant potential as targets for combating streptococcal disease. However, this will depend upon better understanding of their mechanistic basis, and refined mapping of their distribution by epidemiological and metagenomic studies.

Microbiology and Molecular Biology Reviews, 2009

Journal of Dental Research, 2011

Studies on the adherence properties of oral bacteria have been a major focus in microbiology rese... more Studies on the adherence properties of oral bacteria have been a major focus in microbiology research for several decades. The ability of bacteria to adhere to the variety of surfaces present in the oral cavity, and to become integrated within the resident microbial communities, confers growth and survival properties. Molecular analyses have revealed several families of Gram-positive bacterial surface proteins, including serine-rich repeat, antigen I/II, and pilus families, that mediate adherence to a variety of salivary and oral bacterial receptors. In Gram-negative bacteria, pili, auto-transporters, and extracellular matrix-binding proteins provide components for host tissue recognition and building of complex microbial communities. Future studies will reveal in greater detail the binding pockets for these adhesin families and their receptors. This information will be crucial for the development of new inhibitors or vaccines that target the functional regions of bacterial proteins that are involved in colonization and pathogenesis.

Infection and Immunity, 2010

Candida albicans colonizes human mucosa and prosthetic surfaces associated with artificial joints... more Candida albicans colonizes human mucosa and prosthetic surfaces associated with artificial joints, catheters, and dentures. In the oral cavity, C. albicans coexists with numerous bacterial species, and evidence suggests that bacteria may modulate fungal growth and biofilm formation. Streptococcus gordonii is found on most oral cavity surfaces and interacts with C. albicans to promote hyphal and biofilm formation. In this study, we investigated the role of the hyphal-wall protein Als3p in interactions of C. albicans with S. gordonii. Utilizing an ALS3 deletion mutant strain, it was shown that cells were not affected in initial adherence to the salivary pellicle or in hyphal formation in the planktonic phase. However, the Als3(-) mutant was unable to form biofilms on the salivary pellicle or deposited S. gordonii DL1 wild-type cells, and after initial adherence, als3Δ/als3Δ (ΔALS3) cells became detached concomitant with hyphal formation. In coaggregation assays, S. gordonii cells attached to, and accumulated around, hyphae formed by C. albicans wild-type cells. However, streptococci failed to attach to hyphae produced by the ΔALS3 mutant. Saccharomyces cerevisiae S150-2B cells expressing Als3p, but not control cells, supported binding of S. gordonii DL1. However, S. gordonii Δ(sspA sspB) cells deficient in production of the surface protein adhesins SspA and SspB showed &amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;50% reduced levels of binding to S. cerevisiae expressing Als3p. Lactococcus lactis cells expressing SspB bound avidly to S. cerevisiae expressing Als3p, but not to S150-2B wild-type cells. These results show that recognition of C. albicans by S. gordonii involves Als3 protein-SspB protein interaction, defining a novel mechanism in fungal-bacterial communication.

Eukaryotic Cell, 2010

Colonization and infection of the human host by opportunistic pathogen Candida albicans derive fr... more Colonization and infection of the human host by opportunistic pathogen Candida albicans derive from an ability of this fungus to colonize mucosal tissues and prosthetic devices within the polymicrobial communities present. To determine the functions of C. albicans cell wall proteins in interactions with host or bacterial molecules, Saccharomyces cerevisiae was utilized as a surrogate host to express C. albicans cell wall proteins Als3p, Eap1p, Hwp1p, and Rbt1p. Salivary pellicle and fibrinogen were identified as novel substrata for Als3p and Hwp1p, while only Als3p mediated adherence of S. cerevisiae to basement membrane collagen type IV. Parental S. cerevisiae cells failed to form biofilms on salivary pellicle, polystyrene, or silicone, but cells expressing Als3p or Hwp1p exhibited significant attachment to each surface. Virulence factor Rbt1p also conferred lower-level binding to salivary pellicle and polystyrene. S. cerevisiae cells expressing Eap1p formed robust biofilms upon polystyrene surfaces but not salivary pellicle. Proteins Als3p and Eap1p, and to a lesser degree Hwp1p, conferred upon S. cerevisiae the ability to bind cells of the oral primary colonizing bacterium Streptococcus gordonii. These interactions, which occurred independently of amyloid aggregate formation, provide the first examples of specific C. albicans surface proteins serving as receptors for bacterial adhesins.

The Journal of Immunology, Aug 15, 2007

are associated with R5-type HIV-1 targeting the R5-specific coreceptor CCR5, which is not usually... more are associated with R5-type HIV-1 targeting the R5-specific coreceptor CCR5, which is not usually expressed on oral keratinocytes. Because coinfection with other microbes has been suggested to modulate cellular infection by HIV-1, we hypothesized that oral keratinocytes may up-regulate CCR5 in response to the oral endogenous pathogen Porphyromonas gingivalis by cysteineprotease (gingipains) activation of the protease-activated receptors (PARs) or LPS signaling through the TLRs. The OKF6/TERT-2-immortalized normal human oral keratinocyte line expressed CXCR4, whereas CCR5 was not detectable. When exposed to P. gingivalis ATCC 33277, TERT-2 cells induced greater time-dependent expression of CCR5-specific mRNA and surface coreceptors than CXCR4. By comparing arg-(Rgp) and lys-gingipain (Kgp) mutants, a mutant deficient in both proteases, and the action of trypsin, P. gingivalis Rgp was strongly suggested to cleave PAR-1 and PAR-2 to up-regulate CCR5. CCR5 was also slightly up-regulated by an isogenic gingipain-deficient mutant, suggesting the presence of a nongingipain-mediated mechanism. Purified P. gingivalis LPS also up-regulated CCR5. Blocking TLR2 and TLR4 receptors with Abs attenuated induction of CCR5, suggesting LPS signaling through TLRs. P. gingivalis, therefore, selectively up-regulated CCR5 by two independent signaling pathways, Rgp acting on PAR-1 and PAR-2, and LPS on TLR2 and TLR4. By inducing CCR5 expression, P. gingivalis coinfection could promote selective R5-type HIV-1 infection of oral keratinocytes.

Biointerphases, 2016

The formation of biofilms on implant surfaces and the subsequent development of medical device-as... more The formation of biofilms on implant surfaces and the subsequent development of medical device-associated infections are difficult to resolve and can cause considerable morbidity to the patient. Over the past decade, there has been growing recognition that physical cues, such as surface topography, can regulate biological responses and possess bactericidal activity. In this study, diamond nanocone-patterned surfaces, representing biomimetic analogs of the naturally bactericidal cicada fly wing, were fabricated using microwave plasma chemical vapor deposition, followed by bias-assisted reactive ion etching. Two structurally distinct nanocone surfaces were produced, characterized, and the bactericidal ability examined. The sharp diamond nanocone features were found to have bactericidal capabilities with the surface possessing the more varying cone dimension, nonuniform array, and decreased density, showing enhanced bactericidal ability over the more uniform, highly dense nanocone surf...

How Microbial Communities Affect Health and Disease, 2013

Journal of Dentistry, 2015

The aims of this study were to synthesise a range of chlorhexidine-containing nanoparticles (CHX-... more The aims of this study were to synthesise a range of chlorhexidine-containing nanoparticles (CHX-NPs), and investigate the feasibility of using these as an antifungal coating for dental silicones. CHX-NPs were precipitated in aqueous reaction by mixing solutions of CHX digluconate with solutions of sodium triphosphate (TP), trimetaphosphate (TMP) or hexametaphosphate (HMP). CHX-NPs were deposited on commercial dental silicones by immersion coating, and these were characterised for hydrophilicity (contact angle) and water uptake (mass change). Soluble CHX elution into artificial saliva was measured using ultraviolet spectrophotometry. Antifungal efficacy against Candida albicans was investigated using a cell proliferation assay. Coating silicones with CHX-NPs did not significantly affect hydrophilicity, as assessed using water contact angle, or water uptake as assessed by mass change following 16 weeks&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; immersion in artificial saliva. CHX-NP-coated silicone specimens released soluble CHX into artificial saliva. The salt of CHX and the immersion time affected the rate, concentration and duration of CHX release, with CHX-HMP exhibiting a slow, sustained release and CHX-TP and CHX-TMP exhibiting a faster, more concentrated release. C. albicans metabolic activity was inhibited by presence of CHX-HMP-NPs in suspension. CHX-NPs provided a localised, controlled dose of soluble CHX at the surface of dental silicones without adversely affecting hydrophilicity or water uptake. CHX-HMP NPs provided effective antifungal control of C. albicans in a cell proliferation assay. Coating materials with these nanoparticles could be an effective way of delivering low, but clinically relevant, concentrations of chlorhexidine in the oral environment. Denture stomatitis is a common oral infection and is associated with fungal infestation of denture soft lining and obturator materials, which are often silicones such as those used here. Our study suggests that CHX-NPs may be a useful strategy in design of antifungal coatings for these materials.

The Journal of Immunology, 2007

Infection and Immunity, 2008

Streptococcus [GBS]) infection, a leading cause of neonatal sepsis and meningitis. The genes nece... more Streptococcus [GBS]) infection, a leading cause of neonatal sepsis and meningitis. The genes necessary for pilus synthesis and assembly are clustered in pilus islands (PI). Each gene encodes three structural subunits (a backbone and two ancillary proteins) bearing a C-terminal LPXTG motif and two subfamily C sortases (SrtC) involved in covalent polymerization of the subunits. GBS strains also possess the conserved "housekeeping" sortase A (SrtA), but its role in pilus assembly is unclear. To address this issue, pilus expression and cell wall anchoring were analyzed in srtA deletion mutants. Loss of SrtA did not affect pilus polymerization. However, pilus expression on the cell surface was reduced, and pili accumulated in the culture supernatant. Furthermore, cell-associated pili could be readily released by detergent treatment, indicating that SrtA is involved in covalent anchoring of pili to the cell wall. When each of the genes comprising PI-2a was systematically deleted, only the absence of ancillary subunit GBS150 or the SrtC required for incorporation of GBS150 into pili mimicked the srtA mutant phenotype. Thus, from these data a model for GBS pilus assembly can be proposed in which PI sortases are responsible for polymerization of the pilus structure, while SrtA is required to covalently attach it to the cell wall, utilizing ancillary pilus subunit GBS150 as the anchor protein.

Infection and Immunity, 2005

Streptococcus gordonii colonizes multiple sites within the human oral cavity. This colonization d... more Streptococcus gordonii colonizes multiple sites within the human oral cavity. This colonization depends upon the initial interactions of streptococcal adhesins with host receptors. The adhesins that bind salivary agglutinin glycoprotein (gp340) and human cell surface receptors include the antigen I/II (AgI/II) family polypeptides SspA and SspB and a sialic acid-binding surface protein designated Hsa or GspB. In this study we determined the relative functions of the AgI/II polypeptides and Hsa in interactions of S. gordonii DL1 (Challis) with host receptors. For an isogenic mutant with the sspA and sspB genes deleted the levels of adhesion to surfaceimmobilized gp340 were reduced 40%, while deletion of the hsa gene alone resulted in >80% inhibition of bacterial cell adhesion to gp340. Adhesion of S. gordonii DL1 cells to gp340 was sialidase sensitive, verifying that Hsa has a major role in mediating sialic acid-specific adhesion to gp340. Conversely, aggregation of S. gordonii cells by fluid-phase gp340 was not affected by deletion of hsa but was eliminated by deletion of the sspA and sspB genes. Deletion of the AgI/II polypeptide genes had no measurable effect on hsa mRNA levels or Hsa surface protein expression, and deletion of hsa did not affect AgI/II polypeptide expression. Further analysis of mutant phenotypes showed that the Hsa and AgI/II proteins mediated adhesion of S. gordonii DL1 to human HEp-2 epithelial cells. Hsa was also a principal streptococcal cell surface component promoting adhesion of human platelets to immobilized streptococci, but Hsa and AgI/II polypeptides acted in concert in mediating streptococcal cell-platelet aggregation. The results suggest that Hsa directs primary adhesion events for S. gordonii DL1 (Challis) with immobilized gp340, epithelial cells, and platelets. AgI/II polypeptides direct gp340-mediated aggregation, facilitate multimodal interactions necessary for platelet aggregation, and modulate S. gordonii-host engagements into biologically productive phenomena.

Cell Microbiol, 2007

Streptococcus gordonii is a commensal bacterium that colonizes the hard and soft tissues present ... more Streptococcus gordonii is a commensal bacterium that colonizes the hard and soft tissues present in the human mouth and nasopharynx. The cell wallanchored polypeptides SspA and SspB expressed by S. gordonii mediate a wide range of interactions with host proteins and other bacteria. In this article we have determined the role of SspA and SspB proteins, which are members of the streptococcal antigen I/II (AgI/II) adhesin family, in S. gordonii adherence and internalization by epithelial cells. Wild-type S. gordonii DL1 expressing AgI/II polypeptides attached to and was internalized by HEp-2 cells, whereas an isogenic AgI/IImutant was reduced in adherence and was not internalized. Association of S. gordonii DL1 with HEp-2 cells triggered protein tyrosine phosphorylation but no significant actin rearrangement. By contrast, Streptococcus pyogenes A40 showed 50-fold higher levels of internalization and this was associated with actin polymerization and interleukin-8 upregulation. Adherence and internalization of S. gordonii by HEp-2 cells involved b1 integrin recognition but was not fibronectin-dependent. Recombinant SspA and SspB polypeptides bound to purified human a5b1 integrin through sequences present within the NAV (N-terminal) region of AgI/II

Journal of Biological Chemistry, 2016

Streptococcus agalactiae (Group B Streptococcus, GBS) is the predominant cause of early-onset inf... more Streptococcus agalactiae (Group B Streptococcus, GBS) is the predominant cause of early-onset infectious disease in neonates and is responsible for life threatening infections in elderly and immune-compromised individuals. Clinical manifestations of GBS infection include sepsis, pneumonia and meningitis. Here we describe BspA, a deviant antigen I/II family polypeptide that confers adhesive properties linked to pathogenesis in GBS. Heterologous expression of BspA on the surface of the non-adherent bacterium Lactococcus lactis confers adherence to scavenger receptor gp340, human vaginal epithelium, and to the fungus Candida albicans Complementary crystallographic and biophysical characterization of BspA reveal a novel β-sandwich adhesion domain and unique asparagine-dependent super-helical stalk. Collectively these findings establish a new bacterial adhesin structure that has in effect been hijacked by a pathogenic Streptococcus species to provide competitive advantage in human mucosal infections.

Infec Immunity, 2009

The fungus Candida albicans colonizes human oral cavity surfaces in conjunction with a complex mi... more The fungus Candida albicans colonizes human oral cavity surfaces in conjunction with a complex microflora. C. albicans SC5314 formed biofilms on saliva-coated surfaces that in early stages of development consisted of approximately 30% hyphal forms. In mixed biofilms with the oral bacterium Streptococcus gordonii DL1, hyphal development by C. albicans was enhanced so that biofilms consisted of approximately 60% hyphal forms. Cell-cell contact between S. gordonii and C. albicans involved Streptococcus cell wall-anchored proteins SspA and SspB (antigen I/II family polypeptides). Repression of C. albicans hyphal filament and biofilm production by the quorum-sensing molecule farnesol was relieved by S. gordonii. The ability of a luxS mutant of S. gordonii deficient in production of autoinducer 2 to induce C. albicans hyphal formation was reduced, and this mutant suppressed farnesol inhibition of hyphal formation less effectively. Coincubation of the two microbial species led to activation of C. albicans mitogen-activated protein kinase Cek1p, inhibition of Mkc1p activation by H(2)O(2), and enhanced activation of Hog1p by farnesol, which were direct effects of streptococci on morphogenetic signaling. These results suggest that interactions between C. albicans and S. gordonii involve physical (adherence) and chemical (diffusible) signals that influence the development of biofilm communities. Thus, bacteria may play a significant role in modulating Candida carriage and infection processes in the oral cavity.

Pathogens and disease, 2016

Candida-associated stomatitis affects up to 60% of denture wearers, and Candida albicans remains ... more Candida-associated stomatitis affects up to 60% of denture wearers, and Candida albicans remains the most commonly isolated fungal species. The oral bacteria Actinomyces oris and Streptococcus oralis are abundant in early dental plaque. The aims of this study were to determine the effects of S. oralis and A. oris on the development of C. albicans biofilms on denture material. Resin discs were coated with saliva and at early (1.5 h) or later (24 h) stages of biofilm development, cell numbers of each species were determined. Spatial distribution of microorganisms was visualized by confocal scanning laser microscopy of biofilms labelled by differential fluorescence or by fluorescence in situ hybridization. Interkingdom interactions underpinning biofilm development were also evaluated planktonically utilizing fluorescence microscopy. Synergistic interactions between all three species occurred within biofilms and planktonically. Bacterial cells coaggregated with each other and adhered si...