Effects of penicillin on macromolecular synthesis and surface growth of a tolerant streptococcus as studied by computer reconstruction methods

Abstract

Strains of Streptococcus mutans are very susceptible to growth inhibition by benzylpenicillin, but are tolerant to lysis when exposed to even high concentrations of this drug. These properties enabled this study of S. mutans GS-5 surface growth and peptidoglycan, ribonucleic acid, protein, and deoxyribonucleic acid syntheses in the absence of osmotic stabilization. Inhibition of syntheses of peptidoglycan, ribonucleic acid, and protein was dose dependent. Synthesis of peptidoglycan was most susceptible. Substantial but less severe inhibitions of ribonucleic acid and protein syntheses rapidly followed decreased peptidoglycan synthesis, whereas inhibition of deoxyribonucleic acid synthesis was delayed and minimal. Computer-assisted reconstructions of surface growth zones and poles observed in electron micrographs of replicas were performed and indicated that at low concentrations of benzylpenicillin (0.03 micrograms/ml), growth sites reached abnormally large sizes and surface/volume ratios. The observed shifts in surface/volume ratio were attributed to an inhibition of the normal constrictive division mechanism. The poles of these cells also increased in size over those of the controls, but the relatively smaller change in surface/volume ratio confirmed the visual impression that the shape of the poles was much less altered than the shape of the growth sites. As the concentration of benzylpenicillin used was raised from 0.03 to 2 micrograms/ml, the ability of growth sites and poles to enlarge was restricted in a manner that most closely agreed with the extent of inhibition of peptidoglycan (rather than deoxyribonucleic acid, ribonucleic acid, or protein) synthesis. This correlation suggested that increases in cell size may be regulated by the supply of peptidoglycan precursors.

Penicillin-induced lysis of Streptococcus mutans

“…Previous reports (1,(3)(4)(5) have indicated that strains of S. mutans are tolerant to the lytic effects of penicillin G at any concentration tested. The data presented here indicate that S. mutans cells treated with a concentration of penicillin G within a relatively narrow range, and only under certain conditions, do indeed demonstrate cellular lysis.…”

Effects of cell wall inhibitors on cell division in Streptococcus mutans

“…It was interesting to find that, for penicillin G, the concentrations required to inhibit division at the time of onset of C were identical to the concentrations of pencillin G that failed to substantially inhibit surface growth, DNA, RNA, or protein synthesis (5). In contrast, cells treated with high concentrations of penicillin G exhibited inhibition of DNA, RNA, and protein synthe-sis, and cells appeared to be unable to increase their surface (5).…”

“…Therefore, bacteria tolerant to the killing action of these antibiotics are useful tools for examining the effects of antibiotics on cell growth and division. In this study, we examined the effects of various inhibitors of cell wall biosynthesis on division of Streptococcus mutans GS-5, a bacterium previously found to be tolerant- (5). The method of analysis used in this study is based on the cell cycle age distribution of exponential-phase cells which is invariant (2).…”

Penicillin‐induced lysis in fluoride‐resistant mutants of Streptococcus mutans

“…And finally, earlier work with oral streptococci had shown that S. mutans was tolerant to the effects of penicillin (9,21,27). Krai and Callaway (13) have shown that S. mutans GS-5, an organism previously thought to be tolerant to the lytic effects of penicillin (9,21,27) does indeed show penicillin-induced lysis (greater than 90%) under certain conditions. Concentration of penicillin, pH of the medium, and cell density were found to be the three factors critical to effect penicillin-induced cellular lysis.…”