Pseudomonas aeruginosa is an opportunistic pathogen that synthesizes and secretes a wide range of virulence factors. P. aeruginosa poses a potential threat to human health worldwide due to its omnipresent nature, robust host accumulation, high virulence, and significant resistance to multiple antibiotics. The pathogenicity of P. aeruginosa, which is associated with acute and chronic infections, is linked with multiple virulence factors and associated secretion systems, such as the ability to form and utilize a biofilm, pili, flagella, alginate, pyocyanin, proteases, and toxins. Two-component systems (TCSs) of P. aeruginosa perform an essential role in controlling virulence factors in response to internal and external stimuli. Therefore, understanding the mechanism of TCSs to perceive and respond to signals from the environment and control the production of virulence factors during infection is essential to understanding the diseases caused by P. aeruginosa infection and further develop new antibiotics to treat this pathogen. This review discusses the important virulence factors of P. aeruginosa and the understanding of their regulation through TCSs by focusing on biofilm, motility, pyocyanin, and cytotoxins.

Staphylococcus aureus is a common pathogen seen in prosthetic vascular graft, leading to high morbidity and mortality. The virulence genes for severity of infections are under the control of global regulators. Staphylococcal accessory regulator A (SarA) a known master controller of biofilm formation is an attractive target for the drug development. A structure based screening of lead compounds was employed for the identification of novel small molecule inhibitors targeted to interact to the DNA binding domain of the transcriptional activator, SarA and hinder its response over the control of genes that up-regulate the phenotype, biofilm. The top-hit SarA selective inhibitor, 4-[(2,4-diflurobenzyl)amino] cyclohexanol (SarABI) was further validated in-vitro for its efficacy. The SarABI was found to have MBIC50value of 200 μg/ml and also down-regulated the expression of the RNA effector, (RNAIII), Hemolysin (hld), and fibronectin-binding protein (fnbA). The anti-adherence property of SarABI on S. aureus invasion to the host epithelial cell lines (Hep-2) was examined where no significant attachment of S. aureus was observed. The SarABI inhibits the colonization of MDR S. aureus in animal model experiment significantly cohere to the molecular docking studies and in vitro experiments. So, we propose that the SarABI could be a novel substitute to overcome a higher degree of MDR S. aureus colonization on vascular graft.

In Staphylococcus aureus, an important Gram-positive human pathogen, the SaeRS two-component system is essential for the virulence and a good target for the development of anti-virulence drugs. In this study, we screened 12,200 small molecules for Sae inhibitors and identified two anti-cancer drugs, streptozotocin (STZ) and floxuridine (FU), as lead candidates for anti-virulence drug development against staphylococcal infections. As compared with STZ, FU was more efficient in repressing Sae-regulated promoters and protecting human neutrophils from S. aureus-mediated killing. FU inhibited S. aureus growth effectively whereas STZ did not. Intriguingly, RNA-seq analysis suggests that both compounds inhibit other virulence-regulatory systems such as Agr, ArlRS, and SarA more efficiently than they inhibit the Sae system. Both compounds induced prophages from S. aureus, indicating that they cause DNA damages. Surprisingly, a single administration of the drugs was sufficient to protect mice from staphylococcal intraperitoneal infection. Both compounds showed in vivo efficacy in a murine model of blood infection too. Finally, at the experimental dosage, neither compound showed any noticeable side effects on blood glucose level or blood cell counts. Based on these results, we concluded that STZ and FU are promising candidates for anti-virulence drug development against S. aureus infection.

Staphylococcus aureus pathogenesis is an intricate process involving a diverse array of extracellular proteins, biofilm and cell wall components that are coordinately expressed in different stages of infection. The expression of two divergent loci, agr and sar, is increasingly recognized as a key regulator of virulence in S. aureus, and there is mounting evidence for the role of these loci in staphylococcal infections. The functional agr regulon is critical for the production of virulence factors, including α, β and δ hemolysins. The sar locus encodes SarA protein, which regulates the expression of cell wall-associated and certain extracellular proteins in agr-dependent and agr-independent pathways. Multidrug-resistant S. aureus is a leading cause of morbidity and mortality in the world and its management, especially in community-acquired methicillin-resistant S. aureus infections, has evolved comparatively little. In particular, no novel targets have been incorporated into its treatment to date. Hence, these loci appear to be the most significant and are currently at the attention of intense investigation regarding their therapeutic prospects.