Synergistic Killing of Streptococcus pneumoniae with the Bacteriophage Lytic Enzyme Cpl-1 and Penicillin or Gentamicin Depends on the Level of Penicillin Resistance

A combination of Cpl-1, a bacteriophage lytic enzyme, and penicillin, gentamicin, levofloxacin, or azithromycin was tested against Streptococcus pneumoniae strains with various susceptibilities to penicillin. Activities of Cpl-1 and gentamicin were increasingly synergistic with a decreasing penicillin MIC, while Cpl-1 and penicillin showed synergy against an extremely penicillin-resistant strain.