A New Phage Lysin Isolated from the Oral Microbiome Targeting .

is highly pathogenic and causes several mucosal and invasive infections. Due to the rising number of multidrug-resistant (MDR) strains of , new antimicrobials with alternative mechanisms of action are urgently needed. In this study, we identified two new Streptococcal phages from the oral microbiome, 23TH and SA01. Their lysins, 23TH_48 and SA01_53, were recombinantly expressed, characterized and tested for their lethality. SA01_53 was found to only lyse its host strain of , while 23TH_48 was found to possess a broader lytic activity beyond its host strain of , with several isolates sensitive to its lytic activity. 23TH_48 at a concentration of five activity units per mL (U/mL) was found to reduce cell counts of DSM 24048 by 4 log colony forming units per mL (CFU/mL) within 1 h and effectively prevented and destroyed biofilms of R6 at concentrations of 228.8 ng/µL and 14.3 ng/µL, respectively. Given its high lytic activity, 23TH_48 could prove to be a promising candidate to help combat pneumococcal infections.