Biology subjects

Gründling, A.

Publications and source records attributed to Gründling, A..

3 recordsLinked to original sources

bioRxiv2022

Imbalance of peptidoglycan biosynthesis alters the cell surface charge of Listeria monocytogenes

The bacterial cell wall is composed of a thick layer of peptidoglycan and cell wall polymers, which are either embedded in the membrane or linked to the peptidoglycan backbone and referred to as lipoteichoic acid (LTA) and wall teichoic acid (WTA), respectively. Modifications of the peptidoglycan or WTA backbone can alter the susceptibility of the bacterial cell towards cationic antimicrobials and lysozyme. The human pathogen Listeria monocytogenes is intrinsically resistant towards lysozyme, mainly due to deacetylation and O-acetylation of the peptidoglycan backbone via PgdA and OatA. Recent studies identified additional factors, which contribute to the lysozyme resistance of this pathogen. One of these is the predicted ABC transporter, EslABC. An eslB mutant is hyper-sensitive towards lysozyme, likely due to the production of thinner and less O-acetylated peptidoglycan. Using a suppressor screen, we show here that suppression of eslB phenotypes could be achieved by enhancing peptidoglycan biosynthesis, reducing peptidoglycan hydrolysis or alterations in WTA biosynthesis and modification. The lack of EslB also leads to a higher negative surface charge, which likely stimulates the activity of peptidoglycan hydrolases and lysozyme. Based on our results, we hypothesize that the portion of cell surface exposed WTA is increased in the eslB mutant due to the thinner peptidoglycan layer and that latter one could be caused by an impairment in UDP-N-acetylglucosamine (UDP-GlcNAc) production or distribution.

microbiology↗

bioRxiv2022

Purine nucleosides interfere with c-di-AMP levels and act as adjuvants to re-sensitize MRSA to β-lactam antibiotics

Elucidating the complex mechanisms controlling mecA/PBP2a-mediated {beta}-lactam resistance in methicillin resistant Staphylococcus aureus (MRSA) has the potential to identify new drug targets with therapeutic potential. Here, we report that mutations that interfere with de novo purine synthesis (pur operon), purine transport (NupG, PbuG and PbuX) and the nucleotide salvage pathway (DeoD2, Hpt) increased {beta}-lactam resistance in MRSA strain JE2. Extrapolating from these findings, exogenous guanosine and xanthosine, which are fluxed through the GTP branch of purine biosynthesis were shown to significantly reduce MRSA {beta}-lactam resistance. In contrast adenosine, which is fluxed to ATP, significantly increased oxacillin resistance, whereas inosine, which can be fluxed to ATP and GTP via hypoxanthine, only marginally reduced the oxacillin MIC. Increased oxacillin resistance of the nupG mutant was not significantly reversed by guanosine, indicating that NupG is required for guanosine transport, which in turn is required to reduce {beta}-lactam resistance. Suppressor mutants resistant to oxacillin/guanosine combinations contained several purine salvage pathway mutations, including nupG and hpt. Microscopic analysis revealed that guanosine significantly increased cell size, a phenotype also associated with reduced levels of c-di-AMP. Consistent with this, guanosine significantly reduced levels of c-di-AMP, and inactivation of GdpP, the c-di-AMP phosphodiesterase negated the impact of guanosine on {beta}-lactam susceptibility. PBP2a expression was unaffected in nupG or deoD2 mutants suggesting that guanosine-induced {beta}-lactam susceptibility may result from dysfunctional c-di-AMP-dependent osmoregulation. These data reveal the therapeutic potential of purine nucleosides as {beta}-lactam adjuvants that interfere with the normal activation of c-di-AMP required for high-level {beta}-lactam resistance in MRSA. ImportanceThe clinical burden of infections caused by antimicrobial resistant (AMR) pathogens is a leading threat to public health. Maintaining the effectiveness of existing antimicrobial drugs or finding ways to reintroduce drugs to which resistance is widespread is an important part of efforts to address the AMR crisis. Predominantly the safest and most effective class of antibiotics are the {beta}-lactams, which are no longer effective against methicillin resistant Staphylococcus aureus (MRSA). Here we report that the purine nucleosides guanosine and xanthosine have potent activity as adjuvants that can resensitise MRSA to oxacillin and other {beta}-lactam antibiotics. Mechanistically, exposure of MRSA to these nucleosides significantly reduced the levels of the cyclic dinucleotide c-di-AMP, which is required for {beta}-lactam resistance. Drugs derived from nucleotides are widely used in the treatment of cancer and viral infections highlighting the clinical potential of using purine nucleosides to restore or enhance the therapeutic effectiveness of {beta}-lactams against MRSA and potentially other AMR pathogens.

microbiology↗

bioRxiv2020

EslB is required for cell wall Integrity and cell division in Listeria monocytogenes

Lysozyme is an important component of the innate immune system. It functions by hydrolysing the peptidoglycan (PG) layer of bacteria. The human pathogen Listeria monocytogenes is intrinsically lysozyme resistant. The peptidoglycan N-deacetylase PgdA and O-acetyltransferase OatA are two known factors contributing to its lysozyme resistance. Furthermore, it was shown that the absence of components of an ABC transporter, here referred to as EslABC, leads to reduced lysozyme resistance. How its activity is linked to lysozyme resistance is still unknown. To investigate this further, a strain with a deletion in eslB, coding for a membrane component of the ABC transporter, was constructed in L. monocytogenes strain 10403S. The eslB mutant showed a 40-fold reduction in the minimal inhibitory concentration to lysozyme. Analysis of the PG structure revealed that the eslB mutant produced PG with reduced levels of O-acetylation. Using growth and autolysis assays, we show that the absence of EslB manifests in a growth defect in media containing high concentrations of sugars and increased endogenous cell lysis. A thinner PG layer produced by the eslB mutant under these growth conditions might explain these phenotypes. Furthermore, the eslB mutant had a noticeable cell division defect and formed elongated cells. Microscopy analysis revealed that an early cell division protein still localized in the eslB mutant indicating that a downstream process is perturbed. Based on our results, we hypothesize that EslB affects the biosynthesis and modification of the cell wall in L. monocytogenes and is thus important for the maintenance of cell wall integrity. IMPORTANCEThe ABC transporter EslABC is associated with the intrinsic lysozyme resistance of Listeria monocytogenes. However, the exact role of the transporter in this process and in the physiology of L. monocytogenes is unknown. Using different assays to characterize an eslB deletion strain, we found that the absence of EslB not only affects lysozyme resistance, but also endogenous cell lysis, cell wall biosynthesis, cell division and the ability of the bacterium to grow in media containing high concentrations of sugars. Our results indicate that EslB is by a yet unknown mechanism an important determinant for cell wall integrity in L. monocytogenes.

microbiology↗