High-yield production of a functional bacteriophage lysin with antipneumococcal activity using a plant virus-based expression system

•S. pneumoniae phage lysin Pal was produced in a plant virus-based expression system.•Highly pure Pal was obtained after purification by DEAE sepharose.•Plant-produced Pal was active against three tested S. pneumoniae strains.•Pal treatment of bacteremic mice demonstrated a decrease in blood bacterial titers.•Pal protected mice from streptococcal sepsis and death in a dose responsive manner. Streptococcus pneumoniae is the causative agent of several serious infectious diseases. It is becoming increasingly antibiotic resistant worldwide, and thus new antimicrobials are needed. One alternative to antibiotics may be the use of peptidoglycan hydrolases, the bacteriophage lytic enzymes. In this study, we demonstrated high level expression of the S. pneumoniae bacteriophage lysin Pal in Nicotiana benthamiana – TMV (Tobacco Mosaic Virus) transient expression system. The protein was purified to homogeneity and tested for streptococci killing activity in vitro and in vivo. In vitro, Pal was able to lyse three tested S. pneumoniae strains: NCTC12695, NCTC12977 and NCTC11888. The treatment of BALB/c mice with 100μg, 200μg and 400μg of Pal 1h post-challenge with double lethal dose of S. pneumoniae NCTC12695 strain showed a clear dose response and protected from lethal sepsis 30%, 40% and 50% of mice, respectively. The improved mice survival correlated with decreased blood bacterial titers. In conclusion, these results suggest that plant-expressed bacteriophage lysins may have potential use as antimicrobial agents.