Abstract
Streptococcus pneumoniae is one of the most frequently isolated
pathogens that colonize the upper and lower respiratory tract. This
colonization can be responsible for diverse diseases, including otitis
media, pneumonia, among others. Despite the use of pneumococcal
conjugate vaccines, the number of isolated S. pneumoniae continues to be
alarming. In this work, we identified and characterized a novel
endolysin (MSlys) encoded in the pneumococcal phage MS1. We further
performed antimicrobial assays with MSlys against planktonic and biofilm
cells, evaluating their viability before and after treatment.
Additionally, the activity of MSlys on cells was also analyzed using
scanning electron microscopy (SEM) and confocal laser scanning
microscopy (CLSM). MSlys is a modular endolysin carrying a catalytic
domain with amidase activity and a choline-binding domain, folding
mostly in β-sheets. MSlys is active against clinical S. pneumoniae
collected from children with otitis media and in conditions close to
those found in the middle ear. Treatment for 2 h with MSlys (4 µM)
reduced planktonic cultures by 3.5 log10 CFU/mL, and 24- and 48-h-old
biofilms by 1.5 and 1.8 log10 CFU/mL, respectively. Imaging of biofilms
by SEM and CLSM after MSlys treatment showed damaged and thinner biofilm
structures compared to the control samples. The recombinantly expressed
MSlys may be a suitable candidate for the treatment of pneumococcal
infections, including middle ear infections.