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Item Antibacterial, anti-biofilm and anti-virulence activity of biosynthesized silver nanoparticles against drug-resistant Staphylococcus aureus(Springer, 2025-10) Jha, Prabhat NathAntibiotic resistance in bacteria has become a major concern for the effective treatment of infections; therefore, alternatives to antibiotics are being extensively researched to combat drug-resistant microbes. In this study, silver nanoparticles (AgNPs) were biosynthesized using aqueous extracts of papaya leaves (Carica papaya), cannabis leaves (Cannabis sativa), and cardamom (Elettaria cardamomum) and characterized by field-emission scanning electron microscopy (FE-SEM) and UV-visible spectrophotometry. Biosynthesized AgNPs were evaluated for their antibacterial, anti-biofilm, and anti-virulence potential by phenotypic and genotypic methods. AgNPs biosynthesized by all three extracts had spherical morphology and sizes in the nanoscale, average diameter ranging from 46.05 to 94.12 nm. Antibacterial susceptibility testing of S. aureus field isolates under study revealed 48% (24/50) and 38% (19/50) to be resistant to methicillin and amoxycillin-clavulanic acid, respectively. Antibacterial activity of biosynthesized AgNPs against S. aureus strains was determined by the well diffusion method. AgNPs were found to be effective on 90.90% (50/55) S. aureus strains with a zone of inhibition varying from 10 to 21 mm. The AgNPs were also found to be effective on other important bacterial pathogens (viz. Bacillus cereus ATCC 10876, Pseudomonas aeruginosa ATCC 27853, Salmonella Enteritidis ATCC 13070, Escherichia coli ATCC 43888, and Listeria monocytogenes MTCC 657) screened in the study with a ZOI of 15–18 mm. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of AgNPs against S. aureus ranged between 0.015625-0.125 mg/mL and 0.015625-0.25 mg/mL, respectively. In the time kill assay, AgNPs were able to kill S. aureus rapidly within 0.5–1.0 h. In the haemolytic assay, 4–9% haemolysis was observed at concentrations ranging from 0.015625 to 0.25 mg/mL of AgNPs. Biofilm-forming ability of all strains of S. aureus (n = 55) determined by crystal violet assay revealed that 87.27% (48/55) were biofilm formers, while 12.73% (7/55) were non-biofilm formers. Out of 48 biofilm-forming strains, 81.25% (39/48) were strong biofilm producers, 10.41% (5/48) were moderate biofilm producers, and 8.33% (4/48) were weak biofilm producers. Anti-biofilm effect of AgNPs was found at sub-MIC (0.03125 mg/mL), phenotypically. Exopolysaccharide production was found to be reduced by 53.38% indicating the anti-virulence potential of AgNPs at sub-MIC. Relative expression analysis revealed that AgNPs downregulated the expression of biofilm-related genes, namely icaC, icaD, and spa, by 14.2, 10.6, and 8.7-fold, respectively, compared to the control at 3 h of incubation. Other biofilm-related and virulence genes, including icaA, icaB, icaR, agr, ebps, fnb-B, sar-A, and katA, were also found to be downregulated by 7.4, 7.5, 6.2, 5, 4.2, 7.3, 4, and 3.6-fold, respectively, at 3 h. All the target genes were also found to be downregulated at 24 h post-treatment with AgNPs, except icaD, icaR, and agr, which were slightly upregulated. In the present study, AgNPs were successfully biosynthesized and found to possess broad-spectrum antibacterial activity, reduce biofilm formation, and EPS production.Item Natural products acting against S. aureus through membrane and cell wall disruption(RSC, 2023-06) Kumar, GautamStaphylococcus aureus (S. aureus) is responsible for several community and hospital-acquired infections with life-threatening complications such as bacteraemia, endocarditis, meningitis, liver abscess, and spinal cord epidural abscess. In recent decades, the abuse and misuse of antibiotics in humans, animals, plants, and fungi and the treatment of nonmicrobial diseases have led to the rapid emergence of multidrug-resistant pathogens. The bacterial wall is a complex structure consisting of the cell membrane, peptidoglycan cell wall, and various associated polymers. The enzymes involved in bacterial cell wall synthesis are established antibiotic targets and continue to be a central focus for antibiotic development. Natural products play a vital role in drug discovery and development. Importantly, natural products provide a starting point for active/lead compounds that sometimes need modification based on structural and biological properties to meet the drug criteria. Notably, microorganisms and plant metabolites have contributed as antibiotics for noninfectious diseases. In this study, we have summarized the recent advances in understanding the activity of the drugs or agents of natural origin that directly inhibit the bacterial membrane, membrane components, and membrane biosynthetic enzymes by targeting membrane-embedded proteins. We also discussed the unique aspects of the active mechanisms of established antibiotics or new agents.Item Efflux pump inhibitory potential of indole derivatives as an arsenal against norA over-expressing Staphylococcus aureus(ASM, 2023-09) Kumar, GautamNorA, an extensively studied efflux pump in Staphylococcus aureus, has been connected to fluoroquinolone, antiseptic, and disinfection resistance. Several studies have also emphasized how efflux pumps, including NorA, function as the first line of defense of S. aureus against antibiotics. In this study, we have screened some chemically synthesized indole derivatives for their activity as efflux pump inhibitors (EPIs). The derivative SMJ-5 was found to be a potent NorA efflux pump inhibitor among the screened indole derivatives, owing to increased ethidium bromide and norfloxacin accumulation in norA over-expressing S. aureus. The combination of SMJ-5 and ciprofloxacin demonstrated the eradication of S. aureus biofilm and prolonged the post-antibiotic effect more than ciprofloxacin alone. SMJ-5 was able to inhibit staphyloxanthin virulence. In in vitro time-kill trials and in vivo efficacy investigations, the combination enhanced the bactericidal activity of ciprofloxacin against S. aureus. Additionally, reverse transcription PCR results revealed that SMJ-5 also inhibits the NorA efflux pump indirectly at the transcriptional level.