Using next generation antimicrobials to target the mechanisms of infection

Totarol exhibits antibacterial effects through antibiofilm and combined interaction against vancomycin-resistant Enterococcus faecalis

The rise of vancomycin-resistant enterococci (VRE) due to antibiotic overuse poses a significant threat to long-term care patients and those with impaired immune systems. Therefore, it is imperative to seek alternatives to overcome multidrug resistance. This study aimed to evaluate totarol, a natural compound derived from Podocarpus totara, for its antibacterial activity against vancomycin-resistant Enterococcus faecalis (VREF). Totarol exhibited potent antibacterial activity at a very low concentration of 0.25 µg/mL and demonstrated antibiofilm effects through biofilm inhibitory concentration and biofilm eradication concentration assays. Confocal laser scanning microscopy confirmed that totarol inhibited not only biofilm mass but also bacterial cell viability. The combinatorial use of sublethal concentrations of totarol and vancomycin showed antibacterial activity, as observed in the time-kill assay. Quantitative polymerase chain reaction assays revealed a concentration-dependent downregulation of key virulence genes (vanA, ace, asa, efaA, and esp) in VREF when exposed to totarol. In summary, totarol emerges as a promising adjuvant with vancomycin for inhibiting VREF, addressing vancomycin resistance and biofilm formation-critical challenges associated with VRE infection. Since this was an in vitro study, the role of totarol in the clinical implications of VREF treatment remains to be demonstrated.

A Review of Antibacterial Candidates with New Modes of Action

There is a lack of new antibiotics to combat drug-resistant bacterial infections that increasingly threaten global health. The current pipeline of clinical-stage antimicrobials is primarily populated by "new and improved" versions of existing antibiotic classes, supplemented by several novel chemical scaffolds that act on traditional targets. The lack of fresh chemotypes acting on previously unexploited targets (the "holy grail" for new antimicrobials due to their scarcity) is particularly unfortunate as these offer the greatest opportunity for innovative breakthroughs to overcome existing resistance. In recognition of their potential, this review focuses on this subset of high value antibiotics, providing chemical structures where available. This review focuses on candidates that have progressed to clinical trials, as well as selected examples of promising pioneering approaches in advanced stages of development, in order to stimulate additional research aimed at combating drug-resistant infections.

adhesiomeR: a tool for Escherichia coli adhesin classification and analysis

Adhesins are crucial factors in the virulence of bacterial pathogens such as Escherichia coli. However, to date no resources have been dedicated to the detailed analysis of E. coli adhesins. Here, we provide adhesiomeR software that enables characterization of the complete adhesin repertoire, termed the adhesiome. AdhesiomeR incorporates the most comprehensive database of E. coli adhesins and facilitates an extensive analysis of adhesiome. We demonstrate that adhesiomeR achieves 98% accuracy when compared with experimental analyses. Based on analysis of 15,000 E. coli genomes, we define novel adhesiome profiles and clusters, providing a nomenclature for a unified comparison of E. coli adhesiomes.

Physalin H, physalin B, and isophysalin B suppress the quorum-sensing function of Staphylococcus aureus by binding to AgrA

The virulence of Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA), depends on the expression of toxins and virulence factors controlled by the quorum-sensing (QS) system, encoded on the virulence accessory gene regulator (agr) locus. The aim of this study was to identify a phytochemical that inhibits Agr-QS function and to elucidate its mechanism. We screened 577 compounds and identified physalin H, physalin B, and isophysalin B--phytochemicals belonging to physalins found in plants of the Solanaceae family--as novel Agr-QS modulators. Biological analyses and in vitro protein-DNA binding assays suggested that these physalins suppress gene expression related to the Agr-QS system by inhibiting binding of the key response regulator AgrA to the agr promoters, reducing the function of hemolytic toxins downstream of these genes in MRSA. Furthermore, although physalin F suppressed gene expression in the Agr-QS system, its anti-hemolytic activity was lower than that of physalins H, B, and isophysalin B. Conversely, five physalins isolated from the same plant with the ability to suppress Agr-QS did not reduce bacterial Agr-QS activity but inhibited AgrA binding to DNA in vitro. A docking simulation revealed that physalin interacts with the DNA-binding site of AgrA in three docking states. The carbonyl oxygens at C-1 and C-18 of physalins, which can suppress Agr-QS, were directed to residues N201 and R198 of AgrA, respectively, whereas these carbonyl oxygens of physalins, without Agr-QS suppression activity, were oriented in different directions. Next, 100-ns molecular dynamics simulations revealed that the hydrogen bond formed between the carbonyl oxygen at C-15 of physalins and L186 of AgrA functions as an anchor, sustaining the interaction between the carbonyl oxygen at C-1 of physalins and N201 of AgrA. Thus, these results suggest that physalin H, physalin B, and isophysalin B inhibit the interaction of AgrA with the agr promoters by binding to the DNA-binding site of AgrA, suppressing the Agr-QS function of S. aureus. Physalins that suppress the Agr-QS function are proposed as potential lead compounds in the anti-virulence strategy for MRSA infections.