Masaatsu Koike

Cell Wall Alterations of Gram-Negative Bacteria by Aminoglycoside Antibiotics

After treatment with aminoglycoside antibiotics, Escherichia coli B and Pseudomonas aeruginosa P28 showed numerous blebs on the cell wall surface. Images

Inhibition of Cell Division of Escherichia coli by a New Synthetic Penicillin, Piperacillin

The mechanism of the action of piperacillin against Escherichia coli was investigated. This drug converted cells to filaments, but did not show lytic action in a range of concentrations below 25 μg/ml. In some of the filaments, stretched constrictions with various diameters were observed. Addition of piperacillin to a synchronous culture inhibited cell division immediately at any stage of the cell cycle. The results of morphological examination of synchronous cultures show that the percentage of filaments with a stretched constriction corresponds to that of normally septated cells before addition of the drug. Furthermore, peptidoglycan synthesis and cross-linking were not inhibited by this drug. It is likely that this drug inhibits only septum formation, but not the growth of wall, and that stretched constrictions are a result of longitudinal growth of septation caused by the drug. Examination of affinity of the drug to penicillin-binding proteins shows that protein 3 is the most sensitive, proteins 2 and 7 are moderately so, and protein 1 is sensitive only to high concentrations of the drug. Images

Effect of Dihydroxymethyl Furatrizine on Cell Division of Escherichia coli

Antibacterial activities of 3‐di(hydroxymethyl) amino‐6‐[2‐(5‐nitro‐2‐furyl)vinyl]‐1, 2, 4‐triazine, (dihydroxymethyl furatrizine) were investigated using mutant strains of Escherichia coli lacking repair systems for DNA damage, i.e. polA, uvrA, uvrB, uvrC, recA, recB, recC and uvrArecA. All of the mutant strains were more sensitive to the drug than the parent strains, as was the case with the sensitivity to UV‐irradiation. These results indicate that the drug acts lethally on sensitive bacteria by damaging their DNA, and parts of the damaged DNA are repaired by excision and recombinational repair systems. Filamentous cell formation was induced in all strains except the uvrArecA strain by sublethal concentration of the drug, as well as by UV‐irradiation. It is possible that the occurrence of the short period of “unbalanced growth” induced by such DNA damaging agents leads to filament formation. In the cells of the double mutant, filament formation was induced by the drug but not by UV‐irradiation, and the majority of the filamentous cells formed were multinucleated. This suggests that, in this double mutant, the drug directly reacts with the septation machinery of the cell envelope, resulting in filament formation. This hypothesis is supported by the electron microscopic observations that septation is interrupted in the filamentous cells induced by the drug.

Electron microscopic studies on the intracellular structures of Mycobacterium in relation to function

The structure of Mycobacterium has been subjected to intensive investigation, both with light and electron microscopy. Although studies on ultrathin sections of these bacilli have been reported by the present authors (1), Bassermann (2) and Beieger and Glauert (3, 4), the pictures obtained were not sufficient to clarify the individual constituents of the cell. Recently, a mitochondria-like structure was demonstrated by Zapf (5), and Shinohara et al. (6).