ANTIBACTERIAL ACTIVITY OF SILVER NANOPARTICLES AGAINST MULTIDRUG-RESISTANT KLEBSIELLA PNEUMONIAE THROUGH BIOFILM INHIBITION AND VIRULENCE SUPPRESSION

Abstract

Multidrug-resistant Klebsiella pneumoniae has emerged as a major clinical concern because of its extensive antimicrobial resistance, strong biofilm-forming capacity, and multiple virulence determinants that contribute to persistent and difficult-to-treat infections. This study evaluated the antibacterial, antibiofilm, and anti-virulence activities of silver nanoparticles (AgNPs) against MDR K. pneumoniae. A total of 100 clinical isolates were examined, of which 72% were classified as multidrug resistant and 84.7% of MDR isolates demonstrated detectable biofilm formation. Synthesized AgNPs exhibited a characteristic surface plasmon resonance peak at approximately 425 nm, with a mean particle size of 27.6 ± 6.8 nm and a zeta potential of −24.8 ± 2.6 mV. AgNPs showed significant concentration-dependent antibacterial activity, with inhibition zones increasing from 9.8 ± 1.2 mm at 25 µg/mL to 24.9 ± 2.1 mm at 200 µg/mL. MIC and MBC values ranged from 16–128 µg/mL and 32–256 µg/mL, respectively. Biofilm formation was reduced by 28.7%, 56.3%, and 81.6% at ¼ MIC, ½ MIC, and MIC, respectively, while established biofilms were disrupted by up to 78.9% at 2× MIC. Treatment at ½ MIC also decreased siderophore production by 48.6%, bacterial adhesion by 54.2%, and capsule-associated mucoviscosity by approximately 57.1%. Furthermore, fimH, mrkA, mrkD, rmpA, entB, and iucA were significantly downregulated following AgNP exposure. Biofilm biomass exhibited a strong inverse correlation with AgNP concentration (r = −0.88, p < 0.001). Overall, AgNPs demonstrated potent antibacterial, antibiofilm, and anti-virulence effects, supporting their potential as an alternative or adjunctive strategy against MDR K. pneumoniae infections.