Effect of Sublethal Concentrations of Penicillins on the Lysis of Bacteria by Lysozyme and Trypsin

Abstract

Resistance of Staphylococcus aureus and other bacteria to lysis by lysozyme and trypsin is abolished in cultures grown in sublethal concentrations of antibiotics. Antibiotics which inhibit synthesis of the mucopeptide polymer of bacterial cell walls differ widely in their ability to influence the lysis of cell suspensions. Such differences are revealed by both the speed of reduction of turbidity and final level of turbidity reduction. Under the influence of nafcillin, cells of Staphylococcus aureus, Streptococcus faecalis and Diplococcus pneumoniae are readily lysed but Neisseria catarrhalis, Sarcina lutea and Gaffkya tetragena are resistant, suggesting that bacterial cells differ in resistance or susceptibility to enzymic lysis. Lysis is not conditioned by the in vitro antibacterial activity of the antibiotics; nafcillin, which has the same activity against Staphylococcus aureus as oxacillin, cloxacillin, cephalothin, novobiocin and vancomycin, gives a greater rate and extent of lysis than the other antibiotics when used in comparable concentrations. Of the antibiotics interfering with protein synthesis, only erythromycin gives a significant lytic response. The results suggest that sublethal levels of antibiotics may mediate a favorable interplay between the host tissue environment and the parasite.