Mode of action of penicillin

Alterations in the permeability of Neurospora crassa due to polyene antibiotics

Kinsky, Stephen C. (Washington University, St. Louis, Mo.). Alterations in the permeability of Neurospora crassa due to polyene antibiotics. J. Bacteriol. 82:889-897. 1961.-Thirty-three antibiotics and synthetic fungicides were examined for their effect on the growth and morphology of Neurospora crassa. Only the polyene antibiotics (nystatin, amphotericin B, and filipin) caused a decrease in the dry weight of mycelial mats, which was accompanied by the appearance of cytoplasmic constituents in the medium. The influence of polyene concentration, incubation time, mycelial age, various metabolic inhibitors, pH, and media composition on this phenomenon are described. The present evidence indicates that the polyenes exert their primarily fungicidal effect by an alteration of permeability, probably due to direct action on the membrane of sensitive organisms.

The effect of penicillin on the structure of staphylococcal cell walls

Cultures of sensitive stains of Staphylococcus aureus were fixed with osmium tetroxide after 1–5 hours' exposure to various does of pencillin and were embedded in methacrylate for sectioning and electron microscopy. They were compared with untreated, control cultures. The contrast of the cell wall material was untreated, control cultures. The contrast of the cell wall material was increased, by cutting the section of lanthanum nitrate.The cells increased in size and the surrounding cell wall was thinner than normal. The main lesions appeared in the developing cell wall septa, which showed a loss in density and gross irregularity of shape. Some questionable inclusions were seen in the cytoplasm. Lysis was prevented in a medium containing 0.3 M sucrose and the stable spheroplasts retained a recognizable cell wall after 24 hours' exposure to penicillin. However, the septa could not be demonstrated in the cells treated in sucrose medium.Two resistant strains were exposed to penicillin. In one, the cells showed no morphological effects; in the other, there was temporary damage to the cell septa with complete recovery.The observations support the hypothesis that penicillin interferes with the synthesis of a cell wall component and indicate that the main point of cell wall synthesis is at the site of septum formation.

Variation during the cell-division cycle in the penicillin induction of protoplast-like forms of Alcaligenes fecalis

Experiments have been carried out on the penicillin-controlled induction of protoplast-like forms, crescents, in synchronized cultures of a strain of Alcaligenes fecalis. The results have shown that during the cell-division cycle the cell passes through a stage shortly before division during which it is less easily induced to form crescents than at other periods in the division cycle. The data presented indicate that this is not due to a transitory period in the division cycle during which the cell is refractory to penicillin. The findings are discussed in support of the hypothesis that penicillin exerts its effect by destroying some component within the cell whose functioning is necessary for further cell-wall synthesis.

Abnormal growth induced by penicillin in a strain of Alcaligenes fecalis

The effect of penicillin on strain LB of Alcaligenes fccalis has been studied. In tryptone, 50 units/ml. of penicillin transforms the bacillary form of this organism into a protoplast-like structure (globular form) which is capable of exponential growth and division. The division rate of this globular form is about one-half that of the bacillary form. Removal of penicillin results in the reversion of the globular to the bacillary form. Multiplication of the globular form has been found to depend on the presence of some principle present in tryptone not required for bacillary growth in the absence of penicillin. The kinetics of the transformation and reversion process have been studied, leading to the hypothesis that penicillin affects some component: within the cell, this component being concerned with cell division and the elaboration of the cell wall.