Inhibition of Peptidoglycan, Ribonucleic Acid, and Protein Synthesis in Tolerant Strains of Streptococcus mutans

Abstract

Exposure of exponentially growing cultures of Streptococcus mutans strains FA-1 and GS-5 to various concentrations of benzylpenicillin (Pen G) resulted in inhibition of turbidity increases at low concentrations (0.02 to 0.04 ,tg/ml). In many bacterial species, addition of a sufficient concentration of benzylpenicillin (Pen G), or other antibiotic inhibitors of cell wall peptidoglycan (PG) assembly, to prevent further growth of cultures is rapidly followed by cell death, accompanied in many cases by cellular lysis (1,33,34). The availability of bacterial species that are tolerant to both the lethal and the lytic consequences of inhibition of cell wall PG assembly permits studies of the processes that lead to growth inhibition of intact cells without the complications of rapid losses of viability. Furthermore, comparisons of the events occurring in such tolerant species with those occurring in species that are killed by treatment with these drugs will help provide insights into the lytic and other possible mechanisms of lethality. Currently (34), it is clear that the lethal t Present address:

Oxacillin-induced inhibition of protein and RNA synthesis in a tolerant Staphylococcus aureus isolate

“…Only later (1 h) did the rate of protein synthesis decrease. In contrast to the results previously obtained with S. mutans (10), in which the inhibition of protein and RNA synthesis, as measured by pulse-labeling, was very similar, there was a transient increase in RNA synthesis followed by a very rapid decline. Cellular lysis was not observed until 2 h after antibiotic addition.…”

“…The apparatus used to measure and record the turbidity of the experimental culture was previously described (10). Control experiments have shown that this semiautomated system yields growth rates identical to those obtained when the culture is grown in shake flasks.…”

“…The uracil concentration of TSB was undefined by the manufacturer; consequently, the medium used for pulse-labeling experiments was supplemented with uracil to a final concentration of 10 ,gIml. Pulse-labeling experiments were performed as described previously (10). Briefly, a 1.0-ml sample of culture was added to 1.0 ml of uracil-supplemnented TSB containing either 2 …”

“…Standard clinical testing of these organisms shows that the MBC is much greater than the MIC. The biochemical mechanism of this so-called tolerant (12) response of certain strains to normally bactericidal antibiotics is not known; however, one possible explanation suggests the presence, in tolerant strains, of a special form of regulatory "cross talk" such that the almost immediate consequence after inhibition of peptidoglycan synthesis by a beta-lactam antibiotic is the inhibition of protein synthesis (9,10). This inhibition of protein synthesis was postulated to antagonize whatever lytic signal was sent to the cell wall autolytic system of the tolerant bacterium by the beta-lactam antibiotic in the same way that inhibitors of protein synthesis are known to antagonize.…”

Extensive and Genome-Wide Changes in the Transcription Profile ofStaphylococcus aureusInduced by Modulating the Transcription of the Cell Wall Synthesis GenemurF

“…Inhibition of these targets not only causes interference with bacterial growth but also invokes in the cells rapid changes in the pattern of transcription of a large number of genes (11,22,35), suggesting the existence of complex regulatory loops which link a wide variety of steps in metabolism to some steps in cell wall biosynthesis.…”