Antimicrobial potential of Aspergillus oryzae secondary metabolites against carbapenem-resistant Klebsiella pneumoniae

Abstract

The antibacterial potential of Aspergillus oryzae (A. oryzae) EO product (AOEP) extract against Klebsiella pneumoniae (K. pneumoniae) strains BAA-1706 and BAA-1705 was investigated through minimal inhibitory concentration (MIC), biofilm inhibition assays, electron microscopy, and gene expression analysis. AOEP extract exhibited inhibitory activity with MIC₅₀ values ranging from 3.1 % to 50 % for both strains. Notably, AOEP suppressed biofilm formation at low concentrations (3.1 %–12.5 %), outperforming the positive control, kanamycin, at 6.25 %. Morphological examination revealed significant alterations upon AOEP treatment, including reduced colony size and fragmented cells, distinct from kanamycin-induced changes. qRT-PCR demonstrated that AOEP significantly downregulated key virulence genes ompA, lppA, and mrkA in strain BAA-1706, and ompA and lppA in strain BAA-1705, while pal and wzi expression remained unaffected. LC-MS/MS profiling identified several lactone-related secondary metabolites, including acyl homoserine lactone (AHL) analogs and butyrolactone I analogs, suggesting possible quorum sensing interference as a mechanism of action. These findings highlight AOEP extract as a promising multifunctional antibacterial agent that disrupts K. pneumoniae growth, biofilm formation, and virulence, with potential applications in combating antibiotic-resistant infections.