Biology subjects

Satishkumar, N.

Publications and source records attributed to Satishkumar, N..

3 recordsLinked to original sources

bioRxiv2023

Altered PBP4 and GdpP functions synergistically mediate MRSA-like high-level, broad-spectrum β-lactam resistance in Staphylococcus aureus

Infections caused by Staphylococcus aureus are a leading cause of mortality worldwide. S. aureus infections caused by Methicillin-Resistant Staphylococcus aureus (MRSA) are particularly difficult to treat due to their resistance to Next Generation {beta}-lactams (NGB) such as Methicillin, Nafcillin, Oxacillin etc. Resistance to NGBs, which is alternatively known as broad-spectrum {beta}- lactam resistance is classically mediated by PBP2a, a Penicillin-Binding Protein encoded by mecA (or mecC) in MRSA. Thus, presence of mec genes among S. aureus serves as the predictor of resistance to NGBs and facilitates determination of the proper therapeutic strategy for a staphylococcal infection. Although far less appreciated, mecA deficient S. aureus strains can also exhibit NGB resistance. These strains, which are collectively termed as Methicillin-Resistant Lacking mec (MRLM) are currently being identified in increasing numbers among natural resistant isolates of S. aureus. The mechanism/s through which MRLMs produce resistance to NGBs remains unknown. In this study, we demonstrate that mutations that alter PBP4 and GdpP functions, which are often present among MRLMs can synergistically mediate resistance to NGBs. Furthermore, our results unravel that this novel mechanism potentially enables MRLMs to produce resistance towards NGBs at levels comparable to that of MRSAs. Our study, provides a fresh new perspective about alternative mechanisms of NGBs resistance, challenging our current overall understanding of high-level, broad-spectrum {beta}-lactam resistance in S. aureus. It thus suggests reconsideration of the current approach towards diagnosis and treatment of {beta}-lactam resistant S. aureus infections.

microbiology↗

bioRxiv2022

A non-classical mechanism of β-lactam resistance in Methicillin-Resistant Staphylococcus aureus (MRSA) and its effect on virulence

Methicillin-Resistant Staphylococcus aureus (MRSA) are pathogenic bacteria that are infamously resistant to {beta}-lactam antibiotics, a property attributed to the mecA gene. Recent studies have reported that mutations associated with the promoter region of pbp4 demonstrated high levels of {beta}-lactam resistance, suggesting the role of PBP4 as an important non-mecA mediator of {beta}-lactam resistance. The pbp4 promoter-associated mutations have been detected in strains with or without mecA. Our previous studies that were carried out in strains devoid of mecA described that pbp4 promoter-associated mutations lead to PBP4 overexpression and {beta}-lactam resistance. In this study, by introducing various pbp4 promoter-associated mutations in the genome of an MRSA strain, we demonstrate that PBP4 overexpression can supplement mecA-associated resistance in S. aureus and can lead to increased {beta}-lactam resistance. The promoter and regulatory region of pbp4 is shared with a divergently transcribed gene, abcA, which encodes for a multidrug exporter. We demonstrate that the promoter mutations caused an upregulation of pbp4 and downregulation of abcA, confirming that the resistant phenotype is associated with PBP4 overexpression only. PBP4 has also been associated with staphylococcal pathogenesis, however, its exact role remains unclear. Using a C. elegans model, we demonstrate that strains having increased PBP4 expression are less virulent compared to wild-type strains, suggesting that {beta}-lactam resistance mediated via PBP4 likely comes at the cost of virulence. ImportanceOur study demonstrates the ability of PBP4 to be an important mediator of {beta}-lactam resistance in not only Methicillin-susceptible Staphylococcus aureus (MSSA) background strains as previously demonstrated, but also in MRSA strains. When present together, PBP2a and PBP4 overexpression can produce increased levels of {beta}-lactam resistance, causing complications in treatment. Thus, this study suggests the importance of monitoring PBP4-associated resistance in clinical settings, as well as understanding the mechanistic basis of associated resistance, so that treatments targeting PBP4 may be developed. This study also demonstrates that S. aureus strains with increased PBP4 expression are less pathogenic, providing important hints about the role of PBP4 in S. aureus resistance and pathogenesis.

microbiology↗

bioRxiv2021

Loss of GdpP function in Staphylococcus aureus leads to β-lactam tolerance and enhanced evolution of β-lactam resistance

SynopsisO_ST_ABSBackgroundC_ST_ABSWe previously reported the presence of mutations in gdpP among Staphylococcus aureus strains that were obtained by serial passaging in {beta}-lactam drugs. gdpP codes for a phosphodiesterase that cleaves cyclic-di-AMP (CDA), a newly discovered second messenger. ObjectivesWe sought to identify the role of gdpP in {beta}-lactam resistance of S. aureus. MethodsCDA concentrations in bacterial cytosol were measured through mass-spectrometric analysis. gdpP deletion mutagenesis and their complemented strains were created in clinically relevant S. aureus strains to characterize its function. ResultsgdpP associated mutations among passaged strains were identified to cause loss of phosphodiesterase function, leading to increased CDA accumulation in the bacterial cytosol. Deletion of gdpP led to an enhanced ability of the bacteria to withstand a {beta}-lactam challenge (two to three log increase in bacterial colony forming units) by promoting tolerance without enhancing MICs of {beta}-lactam antibiotics. Our results demonstrate that increased drug tolerance due to loss of GdpP function can provide a selective advantage in acquisition of high-level {beta}-lactam resistance and could lead to {beta}-lactam treatment failure of S. aureus infections. ConclusionsLoss of GdpP function increases tolerance to {beta}-lactams that can lead to its therapy failure and can permit {beta}-lactam resistance to occur more readily.

microbiology↗