Production of Polysaccharide by Staphylococcus aureus. IV. Correlation of Lytic Response with Penicillin Activity

Abstract

A previous report(1) from this laboratory has shown that strains of Staphylococcus aureus grown in the presence of subinhibitory concentrations of benzylpenicillin or nafcillin produced a marked accumulation of polysaccharide component within the staphylococcal cell. It was also found that treatment with nafcillin rendered the normally lysozyme-resistant S. aureus susceptible to partial lysis by lysozyme, and that concomitant addition of trypsin resulted in further dissolution of the cell bdies (2). Although the precise cytologic action of subinhibitory levels of penicillin on the integrity of the cell wall of S. aureus is unknown, evidence supported the hypothesis that relatively low concentrations interfered with normal utilization of the polysaccharide by preventing its incorporation into the bacterial cell wall( 1,Z). We also suggested that the accumulation of polysaccharide within the cell might be closely correlated with ability of lysozyme and trypsin to penetrate the cell wall. More recent observations made with subinhibitory concentrations of semisynthetic penicillins nafcillin, oxacillin, and cloxacillin (3) have suggested quantitative differences in their ability to disorganize the cell wall structure of S. aureus.The experimental design reported here was predicated on an initial assumption that changes in the integrity of the cell wall induced by a particular penicillin may fairly accurately reflect the antibacterial activity of that penicillin. Thus it is conceivable that impairment of the cell wall of S. aureus by subinhibitory levels of a penicillin may be correlated with the lytic behavior following treatment with lysozyme and trypsin. If this concept is substantiated, a model system for evaluation of the antibiotic activity of the penicillins could be developed in which pretreatment folIowed by Iytic response would be utilized as a determinative method. As far as ascertained, no studies have been reported that quantitate penicillin activity as a function of the ability to influence enzymic lysis of cells.We attempted in the present study (a) to determine the possible effects of subinhibitory concentrations of nafcillin, oxacillin, and cloxacillin on the enzymic lysis of a number of penicillin-sensitive and penicillin-resistant isolates of S. aweus and (b) to correlate differences in susceptibility to lysis and sensitivity to penicillins. Since lysozyme is present in secretions and certain cells of man and animals, the study may contribute toward a better understanding of the differences observed between the therapeutic action of nafcillin and the isoxazole penicillins in experimental infections in mice(4).Materials and methods. Clinical isolates of S. aureus were obtained from several sources. Minimal inhibitory concentrations (MIC) were determined in brain heart infusion (BHI) by the tube serial dilution technic of Knox ( 5). Benzylpenicillin, nafcillin, oxacillin, and cloxacillin were procured from commercial sources. Stock solutions (1 mg/ml) were prepared in distilled water, sterilized by pas...

Electron Microscopic Study of the Action of Nafcillin on Staphylococcus aureus

“…Previous data reported from this laboratory indicated that strains of Sta phylococcus aureus grown in the presence of low concentrations of nafcil lin are exquisitely sensitive to lysis by lysozyme and trypsin [7,8,9,10]. Evidence was obtained with the electron microscope [5,6] which suggest ed that sublethal concentrations of nafcillin could, during growth of 5. aureus, induce change or damage in the cell wall resulting in an increased vulnerability of the cell to enzymic lysis.…”