Assessing microbial resistance to Artocarpus heterophyllus leaf–mediated AgNO3 colloidal aggregates using adaptive laboratory evolution

Abstract

Abstract Antimicrobial resistance poses a major global health challenge, highlighting the need for alternative antimicrobial strategies. In this study, silver-containing colloidal aggregates were synthesized using an extract from Artocarpus heterophyllus leaves and evaluated for their antimicrobial activity and effects on microbial survival under adaptive conditions. Silver-containing colloidal aggregates were characterized for size, structure, and stability, followed by antimicrobial assessment using Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal/Fungicidal Concentration (MBC/MFC) assays. The synthesized silver-containing colloidal aggregates exhibited an average size of 444.00 ± 32.84 nm, a polydispersity index of 0.81 ± 0.16, and a zeta potential of −24.28 ± 10.66 mV. Functional group analysis indicated that phytochemicals mediated the reduction of Ag⁺ ions. Antimicrobial activity was observed against Escherichia coli, Staphylococcus aureus, and Candida albicans, with MIC values of 80, 640, and 320 mg l−1, respectively, and MBC/MFC values of 1280 mg l−1 (E. coli and C. albicans) and 5120 mg l−1 (S. aureus). Adaptive laboratory evolution (ALE) experiments under gradually increasing silver-containing colloidal particle concentrations showed a progressive decline in microbial growth, with no detectable survival at higher exposure levels. These findings suggest that silver-containing colloidal aggregates exhibit antimicrobial activity and may limit short-term microbial adaptation under the tested conditions.