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.