Bio-generated CoO-NPs from Salvia officinalis: a promising tool against ESBL-producing bacteria

Extended-spectrum β-lactamase (ESBL)-producing bacteria pose significant therapeutic challenges, necessitating the development of alternative antimicrobial agents such as metal nanoparticles. Among 58 bacterial isolates from clinical samples at the National Cancer Institute (Cairo, Egypt), eight ESBL-producing strains were identified (six E. coli and two K. pneumoniae) using phenotypic screening and VITEK 2 system, representing preliminary laboratory findings. GC-MS analysis of Salvia officinalis aqueous extract revealed 16 compounds, with rosmarinic acid (20.41%) as the major constituent. The successful green synthesis of cobalt oxide nanoparticles (CoO-NPs) using S. officinalis was confirmed through UV-visible spectroscopy showing a characteristic peak at 520 nm, HRTEM revealing particle sizes of 10-50 nm, and XRD patterns matching the CoO phase. FTIR spectroscopy confirmed the presence of metal-oxygen bonds and surface functionalization. CoO-NPs demonstrated significant antibacterial activity against ESBL-producing isolates with inhibition zones ranging from 24 to 26 mm and MIC values of 0.312-0.625 mg/ml while enhancing the efficacy of several antibiotics, particularly rifampicin, meropenem, and gentamicin. Antioxidant assays revealed free radical scavenging activity with IC50 values of 513.7 µg/mL and 208 µg/mL for DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,2'-azino-di-[3-ethylbenzthiazoline sulfonate (6)]), respectively. Cytotoxicity studies against normal cell lines showed dose-dependent effects with IC50 values of 303.526 µg/mL for VERO cells and 253.19 µg/mL for OEC cells, with significant morphological changes observed at 500 µg/mL. These preliminary laboratory findings suggest that S. officinalis-mediated CoO-NPs represent a promising therapeutic agent against ESBL-producing bacteria, offering a balance between antimicrobial efficacy and biological safety.