Antibacterial Potential of Green-Synthesized Nanoparticles and Lactic-Acid Bacteria Against Streptococcus Pneumoniae from Ophthalmic Infections

Ophthalmic infections caused by Streptococcus pneumoniae, including conjunctivitis and keratitis, contribute substantially to thea global health burden. Increasing resistance to conventional antibiotics has intensified the need for alternative antimicrobial strategies. This study evaluated and compared the antibacterial potential of lactic acid bacteria (LAB), medicinal plant extracts, and green-synthesized silver nanoparticles (Ag-NPs) against clinical S. pneumoniae isolates from patients with ophthalmic infections. A prospective in vitro experimental study was conducted over six months (January–June 2025). Ocular swabs were collected from 200 patients at Rashid Latif Medical Complex, Lahore, Pakistan. Bacterial isolates were identified using biochemical methods and 16S rRNA molecular characterization. Antibiotic susceptibility was determined using the disc diffusion method according to CLSI guidelines. Antibacterial activities of plant extracts (Azadirachta indica, Andira intermis, Erythrina senegalensis, and Eucalyptus radiata), LAB isolates, and their corresponding green-synthesized Ag-NPs were assessed using the agar well diffusion. Ag-NPs were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Two S. pneumoniae strains were confirmed. Gentamicin and Ceftriaxone showed reduced efficacy, whereas fluoroquinolones demonstrated stronger inhibitory activity. Among plant extracts, E. radiata and A. indica produced the largest inhibition zones. Ag-NPs synthesized from A. intermis and E. radiata showed strong activity, with inhibition zones of 7.00±1.77 mm and 7.20±0.97 mm, respectively. LAB strains P3 and P4 demonstrated the strongest inhibition, measuring 9.57±0.38 mm and 8.73±0.04 mm, respectively. LAB and green-synthesized Ag-NPs demonstrated promising antibacterial activity, highlighting their potential as alternative or adjunctive therapeutic agents for ophthalmic S. pneumoniae infections.