Mette E. Skindersoe

Screening for Quorum-Sensing Inhibitors (QSI) by Use of a Novel Genetic System, the QSI Selector

With the widespread appearance of antibiotic-resistant bacteria, there is an increasing demand for novel strategies to control infectious diseases. Furthermore, it has become apparent that the bacterial life style also contributes significantly to this problem. Bacteria living in the biofilm mode of growth tolerate conventional antimicrobial treatments. The discovery that many bacteria use quorum-sensing (QS) systems to coordinate virulence and biofilm development has pointed out a new, promising target for antimicrobial drugs. We constructed a collection of screening systems, QS inhibitor (QSI) selectors, which enabled us to identify a number of novel QSIs among natural and synthetic compound libraries. The two most active were garlic extract and 4-nitro-pyridine-N-oxide (4-NPO). GeneChip-based transcriptome analysis revealed that garlic extract and 4-NPO had specificity for QS-controlled virulence genes in Pseudomonas aeruginosa. These two QSIs also significantly reduced P. aeruginosa biofilm tolerance to tobramycin treatment as well as virulence in a Caenorhabditis elegans pathogenesis model.

Effects of Antibiotics on Quorum Sensing in Pseudomonas aeruginosa

ABSTRACT During infection, Pseudomonas aeruginosa employs bacterial communication (quorum sensing [QS]) to coordinate the expression of tissue-damaging factors. QS-controlled gene expression plays a pivotal role in the virulence of P. aeruginosa, and QS-deficient mutants cause less severe infections in animal infection models. Treatment of cystic fibrosis (CF) patients chronically infected with P. aeruginosa with the macrolide antibiotic azithromycin (AZM) has been demonstrated to improve the clinical outcome. Several studies indicate that AZM may accomplish its beneficial action in CF patients by impeding QS, thereby reducing the pathogenicity of P. aeruginosa. This led us to investigate whether QS inhibition is a common feature of antibiotics. We present the results of a screening of 12 antibiotics for their QS-inhibitory activities using a previously described QS inhibitor selector 1 strain. Three of the antibiotics tested, AZM, ceftazidime (CFT), and ciprofloxacin (CPR), were very active in the assay and were further examined for their effects on QS-regulated virulence factor production in P. aeruginosa. The effects of the three antibiotics administered at subinhibitory concentrations were investigated by use of DNA microarrays. Consistent results from the virulence factor assays, reverse transcription-PCR, and the DNA microarrays support the finding that AZM, CFT, and CPR decrease the expression of a range of QS-regulated virulence factors. The data suggest that the underlying mechanism may be mediated by changes in membrane permeability, thereby influencing the flux of N-3-oxo-dodecanoyl-l-homoserine lactone.

Quorum sensing antagonism from marine organisms

With the global emergence of multiresistant bacteria there is an increasing demand for development of new treatments to combat pathogens. Bacterial cell–cell communication [quorum sensing (QS)] regulates expression of virulence factors in a number of bacterial pathogens and is a new promising target for the control of infectious bacteria. We present the results of screening of 284 extracts of marine organisms from the Great Barrier Reef, Australia, for their inhibition of QS. Of the 284 extracts, 64 (23%) were active in a general, LuxR-derived QS screen, and of these 36 (56%) were also active in a specific Pseudomonas aeruginosa QS screen. Extracts of the marine sponge Luffariella variabilis proved active in both systems. The secondary metabolites manoalide, manoalide monoacetate, and secomanoalide isolated from the sponge showed strong QS inhibition of a lasB::gfp(ASV) fusion, demonstrating the potential for further identification of specific QS antagonists from marine organisms.

Pseudomonas aeruginosa quorum‐sensing signal molecules interfere with dendritic cell‐induced T‐cell proliferation

Pseudomonas aeruginosa releases a wide array of toxins and tissue-degrading enzymes. Production of these malicious virulence factors is controlled by interbacterial communication in a process known as quorum sensing. An increasing body of evidence reveals that the bacterial signal molecule N-(3-oxododecanoyl)-L-homoserine lactone (OdDHL) exhibits both quorum-sensing signalling and immune-modulating properties. Recently, yet another quorum-sensing signal molecule, the Pseudomonas quinolone signal (PQS), has been shown to affect cytokine release by mitogen-stimulated human T cells. In the present article we demonstrate that both OdDHL and PQS decrease the production of interleukin-12 (IL-12) by Escherichia coli lipopolysaccharide-stimulated bone marrow-derived dendritic cells (BM-DCs) without altering their IL-10 release. Moreover, BM-DCs exposed to PQS and OdDHL during antigen stimulation exhibit a decreased ability to induce T-cell proliferation in vitro. Collectively, this suggests that OdDHL and PQS change the maturation pattern of stimulated DCs away from a proinflammatory T-helper type I directing response, thereby decreasing the antibacterial activity of the adaptive immune defence. OdDHL and PQS thus seem to possess dual activities in the infection process: as inducers of virulence factors as well as immune-modulators facilitating the infective properties of this pathogen.

Cross-contamination: Comparison of Nasal and Chronic Leg Ulcer Staphylococcus aureus Strains Isolated from the Same Patient

The aim of this study was to investigate the occurrence of bacterial cross-contamination between the nasal cavity and leg ulcers. Sixteen patients were included in the study. Staphylococcus aureus was isolated from the leg ulcer of 13 patients and 6 of these patients also harboured S. aureus in the nasal cavity. Klebsiella oxytoca was found in the ulcer and the nasal cavity of one patient. PFGE analysis revealed that patients harbouring S. aureus both in the nasal cavity and the leg ulcer had the same bacterial type at both sites. None of the S. aureus isolates were methicillin resistant.

A Novel Assay for Easy and Rapid Quantification of Helicobacter pylori Adhesion

Reducing adhesion of Helicobacter pylori to gastric epithelial cells could be a new way to counteract infections with this organism. We here present a novel method for quantification of Helicobacter pylori adhesion to cells.

Dual Action of Lysophosphatidate-Functionalised Titanium: Interactions with Human (MG63) Osteoblasts and Methicillin Resistant Staphylococcus aureus.

Titanium (Ti) is a widely used material for surgical implants; total joint replacements (TJRs), screws and plates for fixing bones and dental implants are forged from Ti. Whilst Ti integrates well into host tissue approximately 10% of TJRs will fail in the lifetime of the patient through a process known as aseptic loosening. These failures necessitate revision arthroplasties which are more complicated and costly than the initial procedure. Finding ways of enhancing early (osseo)integration of TJRs is therefore highly desirable and continues to represent a research priority in current biomaterial design. One way of realising improvements in implant quality is to coat the Ti surface with small biological agents known to support human osteoblast formation and maturation at Ti surfaces. Lysophosphatidic acid (LPA) and certain LPA analogues offer potential solutions as Ti coatings in reducing aseptic loosening. Herein we present evidence for the successful bio-functionalisation of Ti using LPA. This modified Ti surface heightened the maturation of human osteoblasts, as supported by increased expression of alkaline phosphatase. These functionalised surfaces also deterred the attachment and growth of Staphylococcus aureus, a bacterium often associated with implant failures through sepsis. Collectively we provide evidence for the fabrication of a dual-action Ti surface finish, a highly desirable feature towards the development of next-generation implantable devices.

Erratum: Dual action of lysophosphatidate-functionalised titanium: Interactions with human (MG63) osteoblasts and methicillin resistant staphylococcus aureus (PLoS ONE 10:11 (e0143509) (DOI:10.1371/journal.pone.0143509))

Dr. Jianxing Zhang should be included in the author byline. He should be listed as the fourth author, and his affiliation #6: Department of Medicinal Chemistry, The University of Utah, Salt Lake City, Utah, United States of America. The contributions of this author are as follows: Conception the design of the work, acquisition and analysis/interpretation of data, synthesized the molecules employed in the experiments, contributed to reagents/materials/analysis tools, drafting as well as revising of the manuscript, and final approval of the published version. The correction citation is: Skindersoe ME, Krogfelt KA, Blom A, Zhang J, Jiang G, Prestwich GD, et al. (2015) Dual Action of Lysophosphatidate-Functionalised Titanium: Interactions with Human (MG63) Osteoblasts and Methicillin Resistant Staphylococcus aureus. PLoS ONE 10(11): e0143509. doi:10.1371/journal.pone.0143509