Biofilm-producing Staphylococcus aureus (S. aureus) is less sensitive to conventional antibiotics than free-living planktonic cells. Here, we evaluated the antibiofilm activity of Illicium verum (I. verum) and one of its constituent compounds 3-hydroxybenzoic acid (3-HBA) against multi-drug-resistant S. aureus. We performed gas chromatography-mass spectroscopy (GC-MS) to identify the major constituents in the methanolic extract of I. verum. Ligand-receptor interactions were studied by molecular docking, and in vitro investigations were performed using crystal violet assay, spreading assay, hemolysis, proteolytic activity, and growth curve analysis. The methanolic extract of I. verum inhibited S. aureus at 4.8 mg/mL, and GC-MS analysis revealed anethole, m-methoxybenzaldehyde, and 3-HBA as the major constituents. Molecular docking attributed the antibiofilm activity to an active ligand present in 3-HBA, which strongly interacted with the active site residues of AgrA and SarA of S. aureus. At a subinhibitory concentration of 2.4 mg/mL, the extract showed biofilm inhibition. Similarly, 3-HBA inhibited biofilm activity at 25 μg/mL (90.34%), 12.5 μg/mL (77.21%), and 6.25 μg/mL (62.69%) concentrations. Marked attrition in bacterial spreading was observed at 2.4 mg/mL (crude extract) and 25 μg/mL (3-HBA) concentrations. The methanol extract of I. verum and 3-HBA markedly inhibited β-hemolytic and proteolytic activities of S. aureus. At the lowest concentration, the I. verum extract (2.4 mg/mL) and 3-HBA (25 μg/mL) did not inhibit bacterial growth. Optical microscopy and SEM analysis confirmed that I. verum and 3-HBA significantly reduced biofilm dispersion without disturbing bacterial growth. Together, we found that the antibiofilm activity of I. verum and 3-HBA strongly targeted the Agr and Sar systems of S. aureus.

Pseudomonas aeruginosa (P. aeruginosa) is one of the common immortal pathogens that cause intense chronic infections in low-immunity patients, significantly evading the immune system and suppressing the respiratory system. This work reports on the synthesis of prominent members of the carbon family, carbon quantum dots (CQDs), from a natural carbon precursor, Citrus medica (C. medica) fruit, and their inhibiting property against P. aeruginosa. CQDs synthesized by the conventional hydrothermal method with an average particle size of 4.5 nm exhibit renowned antimicrobial properties. To enhance the properties of the CQDs, nitrogen was doped using ammonium hydroxide as a nitrogen source, and absorption and fluorescence studies and the elemental composition of CQDs were also reported. CQDs potentially inhibited the growth of bacteria at the lowest concentration level of 1.25% (v/v). Similarly, CQDs moderately inhibited biofilm formation at the concentration level of 0.07% (v/v) for both clinical and control strains of P. aeruginosa. A fluorescence microscopy study revealed that the treated strain shows a moderately reduced biofilm formation when compared to the control strain of P. aeruginosa PAO1.

Acinetobacter baumannii (A. baumannii) is one of the major representative aetiologies of recalcitrant nosocomial infections. Genotypic and phenotypic alterations in A. baumannii have resulted in a significant surge in multidrug resistance (MDR). Of all the factors responsible for the development of antimicrobial resistance (AMR), efflux protein pumps play a paramount role. In pursuit of a safe alternative for the prevention and control of A. baumannii infections, bioactive compounds from the aerial parts of the medicinal plant Artemisia pallens were studied. GC-MS analysis of the ethanol extract of A. pallens detected five major compounds: lilac alcohol A, spathulenol, lilac alcohol C, n-hexadecanoic acid, and vulgarin. In silico examinations were performed using the Schrödinger suite. Homology modelling was performed to predict the structure of the efflux protein of A. baumannii-LAC-4 strain (MDR Ab-EP). The identified bioactive compounds were analysed for their binding efficiency with MDR Ab-EP. High binding efficiency was observed with vulgarin with a glide score of −4.775 kcal/mol and stereoisomers of lilac alcohol A (−3.706 kcal/mol) and lilac alcohol C (−3.706 kcal/mol). Our molecular dynamic simulation studies unveiled the stability of the ligand–efflux protein complex. Vulgarin and lilac alcohol A possessed strong and stable binding efficiency with MDR Ab-EP. Furthermore, validation of the absorption, distribution, metabolism, excretion, and toxicity (ADMET) properties of the ligands strongly suggested that these compounds could serve as a lead molecule in the development of an alternate drug from A. pallens.