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Sarah Osvath

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Technical Officer, Technical Services Research
M Sc

Journal articles

Turnbull, L., Toyofuku, M., Hynen, A.L., Kurosawa, M., Pessi, G., Petty, N.K., Osvath, S.R., Carcamo-Oyarce, G., Gloag, E.S., Shimoni, R., Omasits, U., Ito, S., Yap, X., Monahan, L.G., Cavaliere, R., Ahrens, C.H., Charles, I.G., Nomura, N., Eberl, L. & Whitchurch, C.B. 2016, 'Explosive cell lysis as a mechanism for the biogenesis of bacterial membrane vesicles and biofilms', NATURE COMMUNICATIONS, vol. 7.
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Monahan, L.G., Turnbull, L., Osvath, S.R., Birch, D., Charles, I.G. & Whitchurch, C.B. 2014, 'Rapid conversion of Pseudomonas aeruginosa to a spherical cell morphotype facilitates tolerance to carbapenems and penicillins but increases susceptibility to antimicrobial peptides', Antimicrobial Agents and Chemotherapy, vol. 58, no. 4, pp. 1956-1962.
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The Gram negative human pathogen Pseudomonas aeruginosa is able to tolerate high concentrations of -lactam antibiotics. Despite inhibiting the growth of the organism, these cell wall-targeting drugs exhibit remarkably little bactericidal activity. However, the mechanisms underlying -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 -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 therapeutics to combat bacterial infections.
Gloag, E.S., Turnbull, L., Huang, A., Vallotton, P., Wang, H., Nolan, L.M., Mililli, L., Hunt, C., Lu, J., Osvath, S.R., Monahan, L.G., Cavaliere, R., Charles, I.G., Wand, M., Gee, M., Ranganathan, P. & Whitchurch, C.B. 2013, 'Self-organization of bacterial biofilms is facilitated by extracellular DNA', Proceedings of the National Academy of Sciences of the United States of America, vol. 110, no. 28, pp. 11541-11546.
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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 individual 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
Hollands, A., Pence, M.A., Timmer, A.M., Osvath, S.R., Turnbull, L., Whitchurch, C.B., Walker, M.J. & Nizet, V. 2010, 'Genetic switch to hypervirulence impairs colonization phenotypes of the globally disseminated Group A Streptococcus M1T1 clone', Journal of Infectious Diseases, vol. 202, no. 1, pp. 11-19.
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Background.The recent resurgence of invasive group A streptococcal disease has been paralleled by the emergence of the M1T1 clone. Recently, invasive disease initiation has been linked to mutations in the covR/S 2-component regulator. We investigated whether a fitness cost is associated with the covS mutation that counterbalances hypervirulence. Methods.Wild-type M1T1 group A Streptococcus and an isogenic covS-mutant strain derived from animal passage were compared for adherence to human laryngeal epithelial cells, human keratinocytes, or fibronectin; biofilm formation; and binding to intact mouse skin. Targeted mutagenesis of capsule expression of both strains was performed for analysis of its unique contribution to the observed phenotypes. Results.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.
Arnold, S., Osvath, S.R., Hall, R., King, N. & Sedger, L.M. 2004, 'Regulation of antigen processing and presentation molecules in West Nile virus-infected human skin fibroblasts.', Virology, vol. 225, no. 2, pp. 286-296.
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Infection of humans with the West Nile flavivirus principally occurs via tick and mosquito bites. Here, we document the expression of antigen processing and presentation molecules in West Nile virus (WNV)-infected human skin fibroblast (HFF) cells. Using a new Flavivirus-specific antibody, 4G4, we have analyzed cell surface human leukocyte antigen (HLA) expression on virus-infected cells at a single cell level. Using this approach, we show that West Nile Virus infection alters surface HLA expression on both infected HFF and neighboring uninfected HFF cells. Interestingly, increased surface HLA evident on infected HFF cultures is almost entirely due to virus-induced interferon (IFN)alpha/beta because IFNalpha/beta-neutralizing antibodies completely prevent increased surface HLA expression. In contrast, RT-PCR analysis indicates that WNV infection results in increased mRNAs for HLA-A, -B, and -C genes, and HLA-associated molecules low molecular weight polypeptide-2 (LMP-2) and transporter associated with antigen presentation-1 (TAP-1), but induction of these mRNAs is not diminished in HFF cells cultured with IFNalpha/beta-neutralizing antibodies. Taken together, these data support the idea that that both cytokine-dependent and cytokine-independent mechanisms account for WNV-induced HLA expression in human skin fibroblasts
Sedger, L.M., Hou, S., Osvath, S.R., Glaccum, M.B., Peschon, J.J., van Rooije, N. & Hyland, L. 2002, 'Bone marrow B cell apoptosis during in vivo influenza virus infection requires TNF-alpha and lymphotoxin-alpha.', Journal of Immunology, vol. 169, no. 11, pp. 6193-6201.
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Suppression of bone marrow myeloid and erythroid progenitor cells occurs after infection with a variety of different viruses. In this study, we characterize the alterations in bone marrow (BM) lymphocytes after influenza virus infection in mice. We found a severe loss of BM B cells, particularly CD43(low/-)B220(+) pre-B and immature B cells, in influenza virus-infected mice. Depletion of BM B lineage cells resulted primarily from cell cycle arrest and most likely apoptosis within the BM environment, rather than from increased trafficking of BM emigrants to peripheral lymphoid tissues. Use of gene-knockout mice indicates that depletion of BM B cells is dependent on TNF-alpha, lymphotoxin-alpha, and both TNF receptors, TNFR1-p55 and TNFR2-p75. Thus, TNF-alpha and lymphotoxin-alpha are required for loss of BM B lineage cells during respiratory infection with influenza virus.