Onset of penicillin-induced bacteriolysis in staphylococci is cell cycle dependent

Abstract

Synchronously growing staphylococci were treated with "Ilytic"concentrations of penicillin at different stages of their division cycle. Coulter Counter measurements and light microscopy were used to determine the onset of bacteriolysis. Independent of the stage of the division cycle at which peniciBin was added, (i) the ceUs were always able to perform the next cel division; (ii) the folowing division, however, did not take place; and (iii) instead, at this time, when the onset of the subsequent cell separation was observed in control cultures, lysis of the penicillin-treated cells occurred. These results support a recent model (P. Giesbrecht, H. Labischinski, and J. Wecke, Arch. Microbiol. 141:315-324, 1985) explaining penicillin-induced bacteriolysis of staphylococci as the result of a special morphogenetic mistake during cross wal formation.The mechanism of bacteriolysis by penicillin has been the subject of research for a long time. The many details brought forth by biochemical studies led to different explanations for the lytic death of bacteria. Since the mid-1960s it has been known that penicillin reduces the degree of cross-linking of the bacterial cell wall (28), and the conclusion was that a therefore less-resistant cell wall would no longer be capable of withstanding the relatively high osmotic pressures inside the bacteria. Other investigations showed that with pneumococci, treatment with penicillin induced the release of inhibitors of their autolytic wall enzymes; the resulting triggering of these wall enzymes was regarded as being responsible for lysis (29).In contrast, it has been reported (24, 30) that in the course of a penicillin treatment the autolytic activity of staphylococci decreased rather than increased and that the synthesis of wall material was hardly affected by lytic concentrations of penicillin. Electron microscopic results which showed that even with optimal "lytic" doses of penicillin, staphylococci could build a more or less functioning cross wall (15) and the discovery of new extraplasmatic vesicular structures led to a new model of penicillin-induced bacteriolysis proposed by 13,21). According to this model, penicillin-induced bacteriolysis results from the punching of a few minute holes into the peripheral wall due to the lytic activity of these vesicular structures, which have been named murosomes. Under nonantibiotic conditions, the murosomes perform an essential function: they trigger the cutting process, the first step of cell separation in staphylococci after completion of cell division (13, 21). The lethal event at the relatively low lytic penicillin G concentration (about 0.1 ,ug/ml for the staphylococcal strain used) seemed to be caused by an abnormal local distribution of the wall material synthesized during penicillin G treatment; lytic death occurred as the result of such a special morphogenetic mistake during cross wall formation, which regularly took place when the onset of the normal cell separation process was no longer preceded by sufficient cross wall assembl...

Fan-shaped ejections of regularly arranged murosomes involved in penicillin-induced death of staphylococci

“…Since inhibition of bacteriolysis did not interfere substantially with the killing rate, we conclude that the penicillin-induced death by lytic penicillin concentrations (0.1 ,ug/ml) represents a nonlytic killing process, while bacteriolysis is assumed to be nothing but a postmortem side effect (5). We should, therefore, no longer synonymize "bacteriolysis" with "lytic death" (6,15,22).…”

“…This finding led to the speculation that murosomes might be transported in some way from one division plane to the site of the next cross-wall initiation (6). Furthermore, since only a single murosome-induced wall perforation could be observed in the second division plane in the presence of penicillin, it seemed that only one murosome was involved in the killing process in staphylococci (6,15).…”

“…This killing process involves novel extraplasmatic wall organelles, the murosomes, which in untreated staphylococci regularly punch minute "pores" into the peripheral cell wall above the completed cross wall, thereby initiating cell separation. In the presence of penicillin, however, this separation process is no longer preceded by the assembly of sufficient cross-wall material in the second division plane so that, at the onset of the pore-punching process at this now "unprotected" site of the peripheral wall, the integrity of the wall is destroyed and the cell dies (6,15). Another strictly localized lytic wall process was recently reported to be the very reason for penicillin-induced death in Escherichia coli (12).…”

“…The essential components of the mechanism of penicillininduced death of staphylococci have been elucidated in previous reports (6,15). After the reaction of the ,-lactam antibiotic with the penicillin-binding proteins (2,20), it is not the traditional alteration in the activity of wall autolysins or in cell wall synthesis (22,24) which initiates penicillininduced death (19) but rather a special morphogenetic error incorporated into the cell wall during cross-wall formation.…”

Quantifying Subpopulation Synergy for Antibiotic Combinations via Mechanism-Based Modeling and a Sequential Dosing Design

“…For each population, a life cycle growth model (22,23) was applied that accounts for the underlying biology of bacterial growth (24) and contains bacteria that are preparing for replication (state 1) and bacteria immediately before the replication step (state 2). The transition from state 1 to state 2 occurred via a first-order growth The combination of drug A and drug B will eradiate these bacterial populations due to the lack of a population resistant to both drugs.…”