Antibacterial Activity of <i>Staphylococcus epidermidis</i> <scp>CS05</scp> and <i>Pseudomonas fluorescens</i> <scp>CS83</scp> Isolated From the Human Conjunctival Sac Against Pathogenic Bacterial Reference Strains

The ocular surface hosts commensal bacteria that play essential roles in its development, defense, nutrition, and physiological processes, actively contributing to both innate and adaptive immune responses. However, the inappropriate or excessive use of antibiotics has significantly contributed to the emergence and spread of resistant strains, posing a growing public health challenge. In this context, this study aimed to taxonomically identify and assess the antibacterial potential of the CS05 and CS83 bacterial isolates, obtained from the human conjunctival sac. The latter was accomplished through assays designed to evaluate their ability to inhibit the growth of reference pathogenic strains from the American Type Culture Collection. Antibacterial activity assays, including cross-diffusion, drop agar diffusion, well diffusion, disk diffusion, and polystyrene microplate assays, were performed, and taxonomic identification was carried out by Sanger sequencing. The bacteria CS05 was identified as Staphylococcus epidermidis and demonstrated inhibitory activity against Escherichia coli, Listeria monocytogenes, Bacillus cereus, Enterococcus faecalis, and Staphylococcus aureus. Meanwhile, the isolate CS83, identified as Pseudomonas fluorescens, inhibited the growth of E. coli, L. monocytogenes, Klebsiella pneumoniae, E. faecalis, and S. aureus. These findings suggest that the bacterial microbiota of the human conjunctival sac may represent a promising biotechnological source to develop alternative antibacterial agents.