Pseudomonas aeruginosa is a significant human pathogen, it possesses almost all of the known antimicrobial resistance mechanisms. Quorum sensing (QS) is an intercellular communication system that orchestrates bacterial virulence and its targeting is an effective approach to diminish its pathogenesis. Repurposing of drugs is an advantageous strategy, in this study we aimed to repurpose the anti-diabetic drugs sitagliptin, metformin and vildagliptin as anti-QS in P. aeruginosa. The effects of sub-inhibitory concentrations of the tested drugs on the expression of QS-encoding genes and QS-regulated virulence factors were assessed. The protective activity of tested drugs on P. aeruginosa pathogenesis was evaluated in vivo on mice. In silico analysis was performed to evaluate the interference capabilities of the tested drugs on QS-receptors. Although the three drugs reduced the expression of QS-encoding genes, only sitagliptin inhibited the P. aeruginosa virulence in vitro and protected mice from it. In contrast, metformin showed significant in vitro anti-QS activities but failed to protect mice from P. aeruginosa. Vildagliptin did not show any in vitro or in vivo efficacy. Sitagliptin is a promising anti-QS agent because of its chemical nature that hindered QS-receptors. Moreover, it gives an insight to consider their similar chemical structures as anti-QS agents or even design new chemically similar anti-QS pharmacophores.

Serratia marcescens is an opportunistic nosocomial pathogen and causes wound and burn infections. It shows high resistance to antibiotics and its pathogenicity is mediated by an arsenal of virulence factors. Another therapeutic option to such infections is targeting quorum sensing (QS), which controls the expression of different S. marcescens virulence factors. Prevention of QS can deprive S. marcescens from its bacterial virulence without applying stress on the bacterial growth and facilitates the eradication of the bacteria by immunity. The objective of the current study is to explore the antimicrobial and antivirulence activities of xylitol against S. marcescens. Xylitol could inhibit the growth of S. marcescens. Sub-inhibitory concentrations of xylitol could inhibit biofilm formation, reduce prodigiosin production, and completely block protease activity. Moreover, xylitol decreased swimming motility, swarming motility and increased the sensitivity to hydrogen peroxide. The expression of rsmA, pigP, flhC, flhD fimA, fimC, shlA bsmB, and rssB genes that regulate virulence factor production was significantly downregulated by xylitol. In silico study showed that xylitol could bind with the SmaR receptor by hydrophobic interaction and hydrogen bonding, and interfere with the binding of the natural ligand with SmaR receptor. An in vivo mice survival test confirmed the ability of xylitol to protect mice against the virulence of S. marcescens. In conclusion, xylitol is a growth and virulence inhibitor in S. marcescens and can be employed for the treatment of S. marcescens wound and burn infections.

Diabetic foot ulcers are recognized to be a severe complication of diabetes, increasing the risk of amputation and death. The bacterial infection of Diabetic foot ulcers with virulent and resistant bacteria as Proteus mirabilis greatly worsens the wound and may not be treated with conventional therapeutics. Developing new approaches to target bacterial virulence can be helpful to conquer such infections. In the current work, we evaluated the anti-virulence activities of the widely used antibacterial metronidazole. The minimum inhibitory concentrations (MIC) and minimum biofilm eradication concentrations (MEBC) were determined for selected antibiotics which P. mirabilis was resistant to them in the presence and absence of metronidazole in sub-MIC. The effect of metronidazole in sub-MIC on P. mirabilis virulence factors as production of exoenzymes, motilities, adhesion and biofilm formation, were evaluated. Furthermore, molecular docking of metronidazole into P. mirabilis adhesion and essential quorum sensing (QS) proteins, was performed. The results revealed a significant ability of metronidazole to in-vitro inhibit P. mirabilis virulence factors and antagonize its essential proteins. Moreover, metronidazole markedly decreased the MICs and MBECs of tested antibiotics. Conclusively, metronidazole in sub-MIC is a plausible anti-virulence and anti-QS agent that can be combined to other antibiotics as anti-virulence adjuvant to defeat aggressive infections.

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Bacterial resistance to antibiotics is an increasing public health threat as it has the potential to affect people at any stage of life, as well as veterinary. Various approaches have been proposed to counteract the bacterial resistance development. Tackling bacterial virulence is one of the most promising approaches that confer several merits. The bacterial virulence is mainly regulated by a communication system known as quorum sensing (QS) system. Meanwhile, bacteria can sense the adrenergic hormones and eavesdrops on the host cells to establish their infection, adrenergic hormones were shown to enhance the bacterial virulence. In this study, β-adrenoreceptor blockers were proposed not only to stop bacterial espionage on our cells but also as inhibitors to the bacterial QS systems. In this context, a detailed in silico study has been conducted to evaluate the affinities of twenty-two β-blockers to compete on different structural QS receptors. Among the best docked and thermodynamically stable β-blockers; atenolol, esmolol, and metoprolol were subjected to further in vitro and in vivo investigation to evaluate their anti-QS activities against Chromobacterium violaceum, Pseudomonas aeruginosa and Salmonella typhimurium. The three tested β-blockers decreased the production of QS-controlled C. violaceum, and the formation of biofilm by P. aeruginosa and S. typhimurium. Additionally, the tested β-blockers down-regulated the P. aeruginosa QS-encoding genes and S. typhimurium sensor kinase encoding genes. Furthermore, metoprolol protected mice against P. aeruginosa and S. typhimurium. Conclusively, these investigated β-blockers are promising anti-virulence agents antagonizing adrenergic hormones induced virulence, preventing bacterial espionage, and blocking bacterial QS systems.

The global outbreak of COVID-19 viral infection is associated with the absence of specific drug(s) for fighting this viral infection.

Salmonella enterica is a common cause of many enteric infections worldwide and is successfully engineered to deliver heterologous antigens to be used as vaccines. Clustered Regularly Interspaced Short Palindromic Repeats (CRISPRs) RNA-guided Cas9 endonuclease is a promising genome editing tool. In the current study, a CRISPR-Cas9 system was used to target S.enterica sdiA that encodes signal molecule receptor SdiA and responds to the quorum sensing (QS) signaling compounds N-acylhomoserine lactones (AHLs). For this purpose, sdiA was targeted in both S.enterica wild type (WT) and the ΔssaV mutant strain, where SsaV has been reported to be an essential component of SPI2-T3SS. The impact of sdiA mutation on S. enterica virulence was evaluated at both early invasion and later intracellular replication in both the presence and absence of AHL. Additionally, the influence of sdiA mutation on the pathogenesis S. enterica WT and mutants was investigated in vivo, using mice infection model. Finally, the minimum inhibitory concentrations (MICs) of various antibiotics against S. enterica strains were determined. Present findings show that mutation in sdiA significantly affects S.enterica biofilm formation, cell adhesion and invasion. However, sdiA mutation did not affect bacterial intracellular survival. Moreover, in vivo bacterial pathogenesis was markedly lowered in S.enterica ΔsdiA in comparison with the wild-type strain. Significantly, double-mutant sdiA and ssaV attenuated the S. enterica virulence and in vivo pathogenesis. Moreover, mutations in selected genes increased Salmonella susceptibility to tested antibiotics, as revealed by determining the MICs and MBICs of these antibiotics. Altogether, current results clearly highlight the importance of the CRISPR-Cas9 system as a bacterial genome editing tool and the valuable role of SdiA in S.enterica virulence. The present findings extend the understanding of virulence regulation and host pathogenesis of Salmonellaenterica.

Cysteine-containing dipeptides 3a-l, (3b+3b') (compound numbers in parentheses are used to indicate racemic mixtures; thus (3b+3b') is the racemate of 3b and 3b'), and tripeptide 13 were synthesized in 68-96% yields by acylation of cysteine with N-(Pg-α-aminoacyl)- and N-(Pg-α-dipeptidoyl)benzotriazoles (where Pg stands for protecting group in the nomenclature for peptides throughout the paper) in the presence of Et(3)N. Cysteine-containing peptides 3a-l and 13 were S-acylated to give S-(Pg-α-aminoacyl)dipeptides 5a-l and S-(Pg-α-aminoacyl)tripeptide 14 without racemization in 47-90% yields using N-(Pg-α-aminoacyl)benzotriazoles 2 in CH(3)CN-H(2)O (7:3) in the presence of KHCO(3). (In our peptide nomenclature, the prefixes di-, tri-, etc. refer to the number of amino acid residues in the main peptide chain; amino acid residues attached to sulfur are designated as S-acyl peptides. Thus we avoid use of the prefix "iso".) Selective S-acylations of serine peptide 3k and threonine peptide 3l containing free OH groups were thus achieved in 58% and 72% yield, respectively. S-(Pg-α-aminoacyl)cysteines 4a,b underwent native chemical ligations to form native dipeptides 3f,i via 5-membered cyclic transition states. Microwave irradiation of S-(Pg-α-aminoacyl)tripeptide 15 and S-(Pg-α-aminoacyl)tetrapeptide 17 in the presence of NaH(2)PO(4)/Na(2)HPO(4) buffer solution at pH 7.8 achieved chemical ligations, involving intramolecular migrations of acyl groups, via 11- and 14-membered cyclic transition states from the S-atom of a cysteine residue to a peptide terminal amino group to form native peptides 19 and 20 in isolated yields of 26% and 23%, respectively.