Improved lethal effect of a phage pneumococcal lysozyme by changing the net charge

Abstract

Bacteriophage lytic murein-hydrolases have been proposed as an efficient way to fight bacterial infections. However, the use of these enzymes is normally restricted to Gram-positive bacteria since the outer membrane of the Gram-negative bacteria hampers the access of the protein to its peptidoglycan substrate. All the murein hydrolases reported in the pneumococcal system, both from host or phage origin, depend on the aminoalcohol choline to be fully active. There is only a unique exception to this rule, the Cpl-7 lysozyme, encoded by the lytic pneumococcal phage Cp-7, which instead of the common cell wall binding module recognizing choline, harbors a completely different cell wall module. Studies developed in our laboratories have allowed the improvement of Cpl-7 antibacterial activity by reducing the net charge from -28.8 to -10.85 introducing 15 amino acid substitutions in the cell wall binding module. This modified enzyme, Cpl-7S, was capable to lyse not only the pneumococcal strains tested, including the antibiotic-multiresistant D48 strain, but also a variety of Gram-positive bacteria. We have also designed a standard protocol to destabilize the outer membrane of Gram-negative bacteria and turning them susceptible to the action of Cpl-7S. In this communication, we will present the results of Cpl-7S, which constitutes a promising alternative to kill not only pneumococcal cells but also other important pathogens like Streptococcus pyogenes, and even Gram-negative bacteria after sensitization of the outer membrane. This improved lysozyme, Cpl-7S, has also been tested in zebra fish embryos and conclusions drawn from this new animal model will be discussed.