The human commensal pathogen, Streptococcus pneumoniae, expresses a number of virulence factors that promote serious pneumococcal diseases, resulting in significant morbidity and mortality worldwide. These virulence factors may give S. pneumoniae the capacity to escape immune defenses, resist antimicrobial agents, or a combination of both. Virulence factors also present possible points of therapeutic intervention. The activities of the surface endonuclease, EndA, allow S. pneumoniae to establish invasive pneumococcal infection. EndA’s role in DNA uptake during transformation contributes to gene transfer and genetic diversitifcation. Moreover, EndA’s nuclease activity degrades the DNA backbone of neutrophil extracellular traps (NETs), allowing pneumococcus to escape host immune responses. Given its potential impact on pneumococcal pathogenicity, EndA is an attractive target for novel antimicrobial therapy. Herein, we describe the development of a high-throughput screening assay for the discovery of nuclease inhibitors. Nuclease-mediated digestion of double-stranded DNA was assessed using fluorescence intensity changes of the DNA dye ligand, PicoGreen. Under optimized conditions, the assay provided robust and reproducible activity data (Z'=0.87) and was used to screen 4727 small molecules against an imidazole-rescued variant of EndA. In total, 10 small molecules were confirmed as novel EndA inhibitors that may have utility as research tools for understanding pneumococcal pathogenesis, and ultimately drug discovery
