Biology subjects

van Hensbergen, V. P.

Publications and source records attributed to van Hensbergen, V. P..

4 recordsLinked to original sources

bioRxiv2022

Interference with lipoprotein maturation sensitizes methicillin-resistant Staphylococcus aureus to human group IIA secreted phospholipase A2 and daptomycin.

Methicillin-resistant Staphylococcus aureus (MRSA) has been classified as a high priority pathogen by the World Health Organization underlining the high demand for new therapeutics to treat infections. Human group IIA secreted phospholipase A2 (hGIIA) is among the most potent bactericidal proteins against Gram-positive bacteria, including S. aureus. To determine hGIIA-resistance mechanisms of MRSA we screened the Nebraska Transposon Mutant Library using a sublethal concentration of recombinant hGIIA. We identified and confirmed the role of lspA, encoding the lipoprotein signal peptidase LspA, as a new hGIIA resistance gene in both in vitro assays and an infection model in hGIIA-transgenic mice. Increased susceptibility of the lspA mutant was associated with faster and increased cell wall penetration of hGIIA. Moreover, lspA deletion also increased susceptibility to daptomycin, a last-resort antibiotic to treat MRSA infections. Exposure of MRSA wild-type to the LspA-specific inhibitors globomycin and myxovirescin A1 induced a lspA mutant phenotype with regard to hGIIA and daptomycin killing. Analysis of >26,000 S. aureus genomes showed that LspA is highly sequence-conserved, suggesting that LspA inhibition could be applied universally. The role of LspA in hGIIA resistance was not restricted to MRSA since Streptococcus mutans and Enterococcus faecalis were also more hGIIA-susceptible after lspA deletion or LspA inhibition, respectively. Overall, our data suggest that pharmacological blocking of LspA may disarm Gram-positive pathogens, including MRSA, to enhance clearance by innate host defense molecules and clinically-applied antibiotics.

microbiology↗

bioRxiv2020

Outer membrane permeabilization by the membrane attack complex sensitizes Gram-negative bacteria to antimicrobial proteins in serum and phagocytes

Infections with Gram-negative bacteria form an increasing risk for human health, which is mainly due to the increase in antibiotic resistance. The cell envelope of Gram-negative bacteria consists of an inner membrane, a peptidoglycan layer and an outer membrane, which forms an impermeable barrier to many antibiotics and antimicrobial proteins. The complement system is an important factor of the human immune system that can efficiently kill Gram-negative bacteria via the formation of large pores in the bacterial outer membrane, called Membrane Attack Complexes (MACs). To better understand how these MAC pores damage the complex cell envelope of Gram-negative bacteria, we recently developed a fluorescent reporter system to study membrane damage in E. coli. Here, we used a similar experimental setup in combination with flow cytometry, confocal microscopy and conventional plating assays to elucidate how different components of the immune system act synergistically to effectively clear invading bacteria. We demonstrate how MAC-dependent outer membrane damage enhances the susceptibility of E. coli to further degradation of the cell envelope by lysozyme, leading to drastic changes in the morphology of these bacteria. Furthermore, we elucidate that the MAC enhances the susceptibility of E. coli to phospholipases, and to degradation and killing inside human neutrophils. Altogether, this study provides a detailed overview on how different players of the human immune system work closely together to degrade the complex cell envelope of Gram-negative bacteria. This knowledge may facilitate the development of new antimicrobials that could stimulate, or work synergistically with the immune system.

immunology↗

bioRxiv2018

Genetic insight into zinc and antimicrobial toxicity uncovers a glycerol phosphate modification on streptococcal rhamnose polysaccharides

Cell wall glycopolymers on the surface of Gram-positive bacteria are fundamental to bacterial physiology and infection biology. These structures have also gained interest as vaccine antigens, in particular for the human pathogens Group A Streptococcus (GAS) and Streptococcus mutans. Streptococcal cell wall glycopolymers are considered to be functional homologues of wall teichoic acids but surprisingly lack the biologically-relevant and characteristic anionic charge. Here we identify gacH, a gene of unknown function in the GAS Group A Carbohydrate (GAC) biosynthetic cluster, in two independent transposon library screens for its ability to confer resistance to zinc and susceptibility to the bactericidal enzyme human group IIA secreted phospholipase A2. To understand the underlying mechanism of these phenotypes, we determined the structure of the extracellular domain of GacH and discover that it represents a new family of glycerol phosphate (GroP) transferases. Importantly, we demonstrate the presence of GroP in both the GAC and the homologous Serotype c Carbohydrate (SCC) from S. mutans, which is conferred by gacH and sccH products, respectively. NMR analysis of GAC released from cell wall by non-destructive methods reveals that approximately 30% of the GAC GlcNAc side-chains are modified by GroP at the C6 hydroxyl group. This previously unrecognized structural modification impacts host-pathogen interaction and has implications for vaccine design. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=143 SRC="FIGDIR/small/337519v4_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@6d7598org.highwire.dtl.DTLVardef@435695org.highwire.dtl.DTLVardef@e9515corg.highwire.dtl.DTLVardef@1dc78b7_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2018

Streptococcal Lancefield polysaccharides are critical cell wall determinants for human group IIA secreted phospholipase A2 to exert its bactericidal effects

Human Group IIA secreted phospholipase A2 (hGIIA) is an acute phase protein with bactericidal activity against Gram-positive bacteria. Infection models in hGIIA transgenic mice have suggested the importance of hGIIA as an innate defense mechanism against the human pathogens Group A Streptococcus (GAS) and Group B Streptococcus (GBS). Compared to other Gram-positive bacteria, GAS is remarkably resistant to hGIIA activity. To identify GAS resistance mechanisms, we exposed a highly saturated GAS M1 transposon library to recombinant human hGIIA and compared relative mutant abundance with library input through transposon-sequencing (Tn-seq). Based on transposon prevalence in the output library, we identified nine genes, including dltA and lytR, conferring increased hGIIA susceptibility. In addition, seven genes conferred increased hGIIA resistance, which included two genes, gacH and gacI that are located within the Group A Carbohydrate (GAC) gene cluster. Using GAS 5448 wild-type and the isogenic gacI mutant and gacI-complemented strains, we demonstrate that loss of the GAC N-acetylglucosamine (GlcNAc) side chain in the{Delta} gacI mutant increases hGIIA resistance approximately 10-fold, a phenotype that is conserved across different GAS serotypes. Increased resistance is associated with delayed penetration of hGIIA through the cell wall. Correspondingly, loss of the Lancefield Group B Carbohydrate (GBC) rendered GBS significantly more resistant to hGIIA-mediated killing. This suggests that the streptococcal Lancefield antigens, which are critical determinants for streptococcal physiology and virulence, are required for the human bactericidal enzyme hGIIA to exert its bactericidal function.\n\nAuthor summaryThe human immune system is capable of killing invading bacteria by secreting antimicrobial proteins. Cationic human Group IIA secreted phospholipase A2 (hGIIA) is especially effective against Gram-positive bacteria by degrading the bacterial membrane. HGIIA requires binding to negatively charged surface structures before it can penetrate through the thick peptidoglycan layer and reach the target phospholipid membrane. HGIIA is constitutively expressed at high concentrations at sites of possible bacterial entry, e.g. in tears, skin and small intestine. In serum, normal concentrations are low but can increase up to 1,000-fold upon inflammation or infection. In vitro, ex vivo and in vivo experiments suggest an important role for hGIIA in defense against two human pathogens, Group A and Group B Streptococcus (GAS, GBS). We demonstrate that the Lancefield cell wall polysaccharides that are expressed by these bacteria, the Group A Carbohydrate (GAC) for GAS and the Group B Carbohydrate (GBC) for GBS, are required for optimal hGIIA bactericidal efficacy by facilitating penetration through the peptidoglycan layer. Given the increased hGIIA resistance of antigen-modified or antigen-deficient streptococci, it will be of interest to determine potential regulatory mechanisms regarding expression of streptococcal Lancefield polysaccharides.

microbiology↗