Reconstruction of the Vancomycin-Susceptible Staphylococcus aureus Phenotype From a Vancomycin-Intermediate S. aureus XN108

Asymmetric total synthesis of polycyclic xanthenes and discovery of a WalK activator active against MRSA

The development of new antibiotics continues to pose challenges, particularly considering the growing threat of multidrug-resistant Staphylococcus aureus. Structurally diverse natural products provide a promising source of antibiotics. Herein, we outline a concise approach for the collective asymmetric total synthesis of polycyclic xanthene myrtucommulone D and five related congeners. The strategy involves rapid assembly of the challenging benzopyrano[2,3-a]xanthene core, highly diastereoselective establishment of three contiguous stereocenters through a retro-hemiketalization/double Michael cascade reaction, and a Mitsunobu-mediated chiral resolution approach with high optical purity and broad substrate scope. Quantum mechanical calculations provide insight into stereoselective construction mechanism of the three contiguous stereocenters. Additionally, this work leads to the discovery of an antibacterial agent against both drug-sensitive and drug-resistant S. aureus. This compound operates through a unique mechanism that promotes bacterial autolysis by activating the two-component sensory histidine kinase WalK. Our research holds potential for future antibacterial drug development.

Sub-MIC vancomycin enhances the antibiotic tolerance of vancomycin-intermediate Staphylococcus aureus through downregulation of protein succinylation

Bacteria develop tolerance after transient exposure to antibiotics, and tolerance is a significant driver of resistance. The purpose of this study is to evaluate the mechanisms underlying tolerance formation in vancomycin-intermediate Staphylococcus aureus (VISA) strains. VISA strains were cultured with sub-minimum inhibitory concentrations (sub-MICs) of vancomycin. Enhanced vancomycin tolerance was observed in VISA strains with distinct genetic lineages. Western blot revealed that the VISA protein succinylation (Ksucc) levels decreased with the increase in vancomycin exposure. Importantly, Ksucc modification, vancomycin tolerance, and cell wall synthesis were simultaneously affected after deletion of SacobB, which encodes a desuccinylase in S. aureus. Several Ksucc sites were identified in MurA, and vancomycin MIC levels of murA mutant and Ksucc-simulated (MurA(K69E) and MurA(K191E)) mutants were reduced. The vancomycin MIC levels of K65-MurA(K191E) in particular decreased to 1 mg/L, converting VISA strain K65 to a vancomycin-susceptible S. aureus strain. We further demonstrated that the enzymatic activity of MurA was dependent on Ksucc modification. Our data suggested the influence of vancomycin exposure on bacterial tolerance, and protein Ksucc modification is a novel mechanism in regulating vancomycin tolerance.

Identification and Characterization of a Vancomycin Intermediate-Resistant Staphylococcus haemolyticus Isolated from Guangzhou, China

Background

Staphylococcus haemolyticus is an opportunistic pathogen that belongs to coagulase-negative Staphylococci (CoNS). Increasing infection and multi-drug resistance cases caused by this strain have been reported and thus it poses a great health threat.

Methods

The third-generation sequencing technology was performed on a S. haemolyticus SH-1 isolated from a clinical sample to analyze the drug resistance genes, which included vancomycin resistance related genes. In addition, antimicrobial susceptibility tests, transmission electron microscopy and Triton X-100 stimulated autolysis were conducted to understand its biological characteristics.

Results

The study shows that this clinical isolate is a vancomycin intermediate-resistant strain. Genome comparison also revealed that WalK(N70K) and WalK(R280Q) mutations may contribute to the vancomycin resistant phenotype. Besides, S. haemolyticus SH-1 exhibit common features of thicker cell wall and decreased autolytic activity.

Conclusion

S. haemolyticus SH-1 with WalKR mutations shows typical characteristics of vancomycin resistant strains. Combining the genome features and biological properties, our findings may provide important information for the understanding of the molecular mechanism of S. haemolyticus to vancomycin intermediate-resistance.

Selective Bacteriocins: A Promising Treatment for Staphylococcus aureus Skin Infections Reveals Insights into Resistant Mutants, Vancomycin Resistance, and Cell Wall Alterations

The emergence of antibiotic-resistant S. aureus has become a major public health concern, necessitating the discovery of new antimicrobial compounds. Given that the skin microbiome plays a critical role in the host defence against pathogens, the development of therapies that target the interactions between commensal bacteria and pathogens in the skin microbiome offers a promising approach. Here, we report the discovery of two bacteriocins, cerein 7B and cerein B4080, that selectively inhibit S. aureus without affecting S. epidermidis, a commensal bacterium on the skin. Our study revealed that exposure of S. aureus to these bacteriocins resulted in mutations in the walK/R two-component system, leading to a thickening of the cell wall visible by transmission electron microscopy and subsequent decreased sensitivity to vancomycin. Our findings prompt a nuanced discussion of the potential of those bacteriocins for selective targeting of S. aureus on the skin, given the emergence of resistance and co-resistance with vancomycin. The idea put forward implies that by preserving commensal bacteria, selective compounds could limit the emergence of resistance in pathogenic cells by promoting competition with remaining commensal bacteria, ultimately reducing chronical infections and limiting the spread of antibiotic resistance.

Berberine at sub-inhibitory concentration inhibits biofilm dispersal in Staphylococcus aureus

Staphylococcus aureus is a major human pathogen, which has multiple drug resistance and can cause serious infections. Recent studies have shown that berberine has antibacterial activity and it can affect biofilm formation of S. aureus. However, the berberine effect on the biofilm of S. aureus is controversial. In this study, we investigate the effect of berberine on the biofilm development in S. aureus NCTC8325 and explore the possible mechanism. Susceptibility test shows that berberine inhibits growth of methicillin-sensitive S. aureus (MSSA), methicillin-resistant S. aureus (MRSA) and vancomycin-intermediate S. aureus (VISA) at different concentrations. S. aureus NCTC8325 is chosen as a model strain to explore further the berberine effect. The MIC of berberine for S. aureus NCTC8325 is 256 µg ml^-1. Berberine below 32 µg ml^-1 inhibits the dispersal of biofilm and stimulates clumping of cells of NCTC8325 in a concentration-dependent manner, while not showing obvious inhibition on the bacterial growth. The transcription of the key negative regulator of biofilm dispersal AgrA is decreased and an agrA mutant forms biofilm reaching to a similar level of biomass to WT in the presence of berberine at 32 µg ml^-1. Transcription of some genes involving synthesis of biofilm structure components, including polysaccharide intracellular adhesin (PIA), proteins and eDNA were also up-regulated, especially icaA for PIA synthesis. And consistently, PIA content was increased in cells exposed to berberine at 32 µg ml^-1. This study reveals the dependence of berberine inhibition of biofilm dispersal on the Agr system, which is the first report exploring the molecule mechanism of the berberine effect on the biofilm of S. aureus.

A vancomycin resistance-associated WalK(S221P) mutation attenuates the virulence of vancomycin-intermediate Staphylococcus aureus

INTRODUCTION

Vancomycin-intermediate Staphylococcus aureus (VISA) is typically associated with a decline in virulence. We previously reported a WalK(S221P) mutation that plays an important role in mediating vancomycin resistance in VISA XN108. Whether this mutation is implicated in bacterial virulence remains unknown.

OBJECTIVES

This study aimed to investigate the effect of WalK(S221P) mutation on the virulence of VISA and the underlying mechanism of this effect.

METHODS

The influence of WalK(S221P) mutation on VISA virulence and its underlying mechanism were explored using animal models, RNA-seq analysis, RT-qPCR, hemolytic assay, slide coagulase test, Western blot, β-galactosidase assay, and electrophoresis mobility shift assay (EMSA).

RESULTS

Compared with XN108, WalK(S221P)-reverted strain XN108-R exacerbated cutaneous infections with increased lesion size and extensive inflammatory infiltration in mouse models. The bacterial loads of S. aureus XN108-R in murine kidney increased compared with those of XN108. RNA-seq analysis showed upregulation of a set of virulence genes in XN108-R, which exhibited greater hemolytic and stronger coagulase activities compared with XN108. Introduction of WalK(S221P) to methicillin-resistant S. aureus USA300 and methicillin-susceptible strain Newman increased the vancomycin resistance of the mutants, which exhibited reduced hemolytic activities and decreased expression levels of many virulence factors compared with their progenitors. WalK(S221P) mutation weakened agr promoter-controlled β-galactosidase activity. EMSA results showed that WalK-phosphorylated WalR could directly bind to the agr promoter region, whereas WalK(S221P)-activated WalR reduced binding to the target promoter. Inactivation of agr in S. aureus did not affect their vancomycin susceptibility but mitigated the virulence alterations caused by WalK(S221P) mutation.

CONCLUSION

The results of our study indicate that WalK(S221P) mutation can enhance vancomycin resistance in S. aureus of diverse genetic backgrounds. WalK(S221P)- bearing S. aureus strains exhibit reduced virulence. WalK(S221P) mutation may directly impair the activation of the agr system by WalR, thereby decreasing the expression of virulence factors in VISA.

The Role of Staphylococcus aureus YycFG in Gene Regulation, Biofilm Organization and Drug Resistance

Antibiotic resistance is a serious global health concern that may have significant social and financial consequences. Methicillin-resistant Staphylococcus aureus (MRSA) infection is responsible for substantial morbidity and leads to the death of 21.8% of infected patients annually. A lack of novel antibiotics has prompted the exploration of therapies targeting bacterial virulence mechanisms. The two-component signal transduction system (TCS) enables microbial cells to regulate gene expression and the subsequent metabolic processes that occur due to environmental changes. The YycFG TCS in S. aureus is essential for bacterial viability, the regulation of cell membrane metabolism, cell wall synthesis and biofilm formation. However, the role of YycFG-associated biofilm organization in S. aureus antimicrobial drug resistance and gene regulation has not been discussed in detail. We reviewed the main molecules involved in YycFG-associated cell wall biosynthesis, biofilm development and polysaccharide intercellular adhesin (PIA) accumulation. Two YycFG-associated regulatory mechanisms, accessory gene regulator (agr) and staphylococcal accessory regulator (SarA), were also discussed. We highlighted the importance of biofilm formation in the development of antimicrobial drug resistance in S. aureus infections. Data revealed that inhibition of the YycFG pathway reduced PIA production, biofilm formation and bacterial pathogenicity, which provides a potential target for the management of MRSA-induced infections.

Open-label prospective therapeutic clinical trials: oral vancomycin in children and adults with primary sclerosing cholangitis

BACKGROUND

Oral vancomycin (OV) in primary sclerosing cholangitis (PSC) has been evaluated as a potential therapeutic agent. We report the long-term biochemical course and outcomes of patients with PSC treated with OV.

METHODS

Patients were enrolled in 2 open-label clinical trials (ClinicalTrials.gov Identifier: NCT01802073 and NCT01322386) and offered OV at 50 mg/kg/day in 3 divided doses if weight <30kg, and 500 mg 3 times/day if weight ≥30kg. Patients with biliary strictures requiring stenting or awaiting liver transplant were excluded. Liver biochemistry, MRCP and histology were documented at baseline and while on OV. The primary outcome was a decrease in elevated gamma glutamyl transferase (GGT), alkaline phosphatase (ALP), and/or alanine aminotransferase (ALT) from baseline.

RESULTS

30 subjects were enrolled, and 29 additional subjects who learned of the clinical trial requested OV (total n = 59; median age was 13.5 years [range, 1.5-44 years]; 64.4% were male; and 94.9% had inflammatory bowel disease [IBD]). The median treatment duration was 2.7 years (range, 0.2-14 years). Ninety-six percent (57/59), 81.3% (48/59), and 94.9% (56/59) experienced reduction of GGT, ALP, and ALT, respectively. Furthermore, 39% (23/59), 22% (13/59), and 55.9% (33/59) experienced normalization of GGT, ALP, and ALT, respectively, within the first 6 months of OV treatment. One patient underwent liver transplantation 8 years after beginning OV treatment, and one developed biliary strictures requiring endoscopic intervention. OV was well-tolerated by patients, and no patient developed treatment-related adverse events.

CONCLUSION

In PSC, OV was well-tolerated and was associated with improvement in liver chemistry. A randomized placebo-controlled clinical trial is warranted.

Two-component signaling pathways modulate drug resistance of (Review)

As the issues surrounding antibiotic-resistant strains of Staphylococcus aureus (S. aureus) are becoming increasingly serious concerns, it is imperative to investigate new therapeutic targets to successfully treat patients with S. aureus infections. The two-component signal transduction system is one of the primary pathways by which bacteria adapt to the external environment, and it serves an important role in regulating virulence gene expression, cell wall synthesis, biofilm formation and bacterial activity. There are 17 two-component signaling pathways in S. aureus, among which WalKR/VicSR/YycGF, AirSR/YhcSR, vancomycin resistance associated regulator/sensor and LytRS have been demonstrated to serve vital roles in regulating bacterial resistance, and are hypothesized to be potential targets for the treatment of S. aureus infections. The present review assesses the mechanism of the two-component signaling pathways associated with the development of S. aureus resistance.