Exploration of the novel fluoroquinolones with high inhibitory effect against quinolone-resistant DNA gyrase of Salmonella Typhimurium

Targeting lon protease to inhibit persister cell formation in Salmonella Typhimurium: a drug repositioning approach

Objective

Persister cells are a specific subset of bacteria capable of surviving exposure to lethal doses of antibiotics, leading to antibiotic therapy failures and infection relapses. This research explores the utilization of drug repositioning to target the Lon protease in Salmonella Typhimurium.

Method

In this study, FDA-approved drugs sourced from the Drug Bank database were screened to identify existing pharmaceuticals with the potential to combat the Lon protease. The formation of persister cells in the presence of antibiotics, as well as the combination of antibiotics with potential Lon protease inhibitors, was examined. Furthermore, the expression of type II toxin-antitoxin system genes was analyzed to enhance our comprehension of the inhibitors' effects.

Result

Molecular docking analysis revealed that Diosmin and Nafcillin exhibited strong binding affinity to the Lon protease. Molecular dynamics simulation trajectories analysis demonstrated that the interaction of these ligands with the enzyme did not induce instability; rather, the enzyme's structure remained stable. Combinations of ceftazidime and ciprofloxacin with either Nafcillin or Diosmin led to significant reductions in bacterial cell counts. Furthermore, the effectiveness of these combinations, when compared to antibiotics alone, highlighted the substantial impact of Nafcillin and Diosmin in reducing type II TA system gene expression.

Conclusion

These findings suggest promising prospects for developing novel therapeutic approaches targeting persister cells to mitigate treatment failures in Salmonella infections.

Schematic-portfolio of potent anti-microbial scaffolds targeting DNA gyrase: Unlocking ways to overcome resistance

Drug development process demands validation of specific drug target impeding the Multi Drug Resistance (MDR). DNA gyrase, as a bacterial target has been in trend for developing newer antibacterial candidates due to its absence in higher eukaryotes. The fluoroquinolones are the leading molecules in the drug discovery pipeline for gyrase inhibition due to its diversity. The fluoroquinolones like levofloxacin and moxifloxacin have been listed in class A drugs for treating MDR. Gatifloxacin and ciprofloxacin also proved its efficacy against MDR TB and MDR enteric fever in adults, whereas nemonoxacin can induce anti-MDR activity of other antibiotics already suggested by studies. Though fluoroquinolones already proved its effectiveness against gyrase, other molecules viz., benzothiazinone, phenyl pyrrolamide, substituted oxadiazoles, triazolopyrimidine, arylbenzothiazole, coumarinyl amino alcohols and ciprofloxacin uracil, can inhibit the target more precisely. The structure-activity-relationships of the different scaffolds along with their synthetic strategies have been deciphered in the current review. Also, the naturally occurring compounds along with their extraction procedure have also been highlighted as potent DNA gyrase inhibitors. In addition to fluoroquinolone, the natural compounds novobiocin and simocyclinone could also inhibit the gyrase, impressively which has been designed with the gyrase structure for better understanding. Herein, ongoing clinical development of some novel drugs possessing triazaacenaphthylenes, spiropyrimidinetriones, and oxazolidinone-quinolone hybrids have been highlighted which could further assist the future generation antibiotic development corroborating gyrase as a potential target against MDR pathogens.

Prevalence of Indigenous Antibiotic-Resistant Salmonella Isolates and Their Application to Explore a Lytic Phage vB_SalS_KFSSM with an Intra-Broad Specificity

The consumption of fresh produce has led to increase in antibiotic-resistant (AR) Salmonella outbreaks. In this study, indigenous Salmonella was isolated from a total of two hundred-two samples including fresh produce and agricultural environmental samples in Korea. After biochemical confirmation using the Indole, Methyl Red, Voges-Proskauer, Citrate tests, presumable Salmonella isolates were identified by 16S rRNA sequencing. Identified Salmonella isolates were evaluated for antibiotic susceptibility against twenty-two antibiotics. The specificity and the efficiency of plating (EOP) of vB_SalS_KFSSM were evaluated against fifty-three bacterial strains. Twenty-five suspected Salmonella were isolated and confirmed by the positive result for methyl red and citrate, of which ten were identified as Salmonella spp. through 16S rRNA gene sequencing. Eight Salmonella isolates (4.0%, n = 8/202) were resistant to at least one antibiotic, among which five were multi-drug resistant. As a lytic phage against Salmonella spp. CMGS-1, vB_SalS_KFSSM was isolated from cow manure. The phage was observed as a tailed phage belonging to the class Caudoviricetes. It exhibited an intra-broad specificity against four indigenous AR Salmonella isolates, two indigenous Salmonella isolates, and five other Salmonella serotypes with great efficiencies (EOP ≥ 0.75). Thus, this study suggested the potential of vB_SalS_KFSSM to combat indigenous AR Salmonella.