A selective medium containing 25 to 50 μg per ml of tunicamycin was devised to isolate micromonosporae from soil samples, making possible simple, preferential isolation of a variety of Micromonospora. When a large amount of Gram-negative bacteria was present in a sample, alkaline treatment (0.01 N NaOH, 5-10 minutes at 15°C) was employed to reduce the numbers. Using the tunicamycin agar medium, 1, 585 strains of presumably different micromonosporae were obtained from 400 soil samples collected from various regions around the world. In average, 4 different Micromonospora strains could be isolated from one soil sample. This tunicamycin method made possible a concentrated screening method for new antibiotics from Micromonospora.

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Demethylation of Co-bleomycin A₂ by heating yields three different complexes: form I and form II and "orange" Co-bleomycin-demethyl A₂. These complexes can be separated by HPLC and show different 1H NMR spectra. Preparation of Co-bleomycin-demethyl A₂by chelation of bleomycin-demethyl A₂ with cobalt yields a Co-bleomycin-demethyl A₂, which is auto-oxidized into Co-bleomycin A₁.

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A pharmacokinetic model has been developed, by means of which all possible time courses of the concentrations of antibiotics in the plasma of treated individuals can be exactly simulated in vitro without diluting the test organism and affecting the growth curves. Equieffective concentrations in the system corresponded to the plasma concentrations in man produced by cefroxadine in a single oral dose of 250 mg and cephalexin and cephradine in a single oral dose of 500 mg.

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Gentamicin, tobramycin, netilmicin, kanamycin and amikacin were evaluated over time for biologic activity in human serum, in combination with 6 β-lactams. Simple addition of aminoglycoside and 250 μg/ml penicillin produced aminoglycoside inactivation at 8-48 hours. However, all β-lactam antibiotics exhibited decay in human serum at 37°C, even when present as a single component. All aminoglycosides could be inactivated by penicillins but differed markedly in their susceptibility. Amikacin, at 20 μg/ml, was the least inactivated by any penicillin; netilmicin, at 10 μg/ml, was the next least inactivated. Tobramycin had pronounced loss of biological activity exceeding that of any aminoglycoside, appearing as early as 8 hours. The ability of the various penicillins to produce aminoglycoside inactivation, in approximate descending order, was; carbenicillin, ticarcillin, penicillin G, oxacillin, methicillin, ampicillin. Cephalothin produced minimal inactivation. Aminoglycoside inactivation also occurred at 25°C, and with many samples stored at 4°C, although at proportionately slower rates. For samples stored at -20°C, only tobramycin had substantial loss of activity. These data indicate that adequate handling and prompt assay of the specimen are important.

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Synergistic effects of the cell wall-affecting antibiotics, dibekacin (DKB) and fosfomycin (FOM) and a macrolide antibiotic, midecamycin (MDM) or its derivative 9, 3"-di-O-acetylmidecamycin (MOM) against Pseudonionas aeruginosa were investigated in vitro and in vivo.
Synergistic effects were evaluated by estimating the number of viable bacteria at varying intervals after the two kinds of antibiotics were added to the logarithmic phase of the bacterial solution. Six hours after addition of antibiotic, the viable bacterial count of the culture treated with FOM and MOM underwent 2 log reduction compared to that which treated with FOM alone. Thus synergistic effect was significant. The number of viable bacteria treated with DKB and MDM showed slight reduction at 3 hours after addition of the two antibiotics and a marked reduction was noted after 20 hours compared with the control. Synergistic action was also demonstrated in in vivo experiments using mice. Three experimental mouse infection models, intraperitoneal infection, subcutaneous infection with carrageenan solution and burn infection were used. FOM was administered subcutaneously. DKB was administered intramuscularly. MDM or MOM was administered by the oral route. In all three experiments the survival rate of infected mice treated with FOM and MOM increased significantly compared to control mice. Similar synergistic effect was also obtained with DKB and MDM.

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The macrolide [¹³H]dihydrorosaramicin binds specifically to 50S and 70S bacterial ribosomal particles. We have studied the influence of salts, pH and additives on the interaction and found that the optimum requirement for salts was 10 mM tris-HCl (pH 7.6), 6 mM MgCl₂, 60 mM NH₄Cl, and the β-mercaptoethanol which reacts on rosaramicin and its dihydro derivative cannot be used. The parameters of the binding were not dependent on the technique used, i.e. equilibrium dialysis, ethanol precipitation or two-phase partitioning. In our search for effectors of this binding, we have found that it is inhibited by other macrolides, little effected by tobramycin and chloramphenicol and enhanced by puromycin.

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Inhibition of protein synthesis by trichodermol, diacetoxyscirpenol and verrucarin A in cells and spheroplasts of Saccharomyces cerevisiae was investigated. Inhibition was reversible for trichodermol and diacetoxyscirpenol, both drugs being removed from their target site(s) by washing, but was irreversible for verrucarin A. These results are interpreted in relation to variations in chemical structure between these trichothecenes.

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The single intratracheal instillation of bleomycin sulfate (0.5mg (potency) per 100g body weight) in hamsters rapidly increased the activity of glucosamine 6-phosphate synthetase (EC 2.6.1.16) of the lung, a major regulatory enzyme for the synthesis of acidic glycosaminoglycan (AGAG). The activity increased as early as day 2, reached maximum level at day 10, then decreased and returned to the control level at day 45. The content of AGAG was also in creased by bleomycin treatment, but the increase of AGAG followed the elevation of the enzyme activity. These results suggest that the early elevation of glucosamine 6-phosphate synthetase activity is closely related to the accumulation of AGAG in the fibrosing lung caused by bleomycin.

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The mechanism of action of geldanamycin, a benzoquinoid ansamycin, was investigated with murine lymphoblastoma L5178Y cells. The agent inhibited the cell growth at concentrations over 0.01μg/ml. The antibiotic blocked DNA synthesis more markedly than RNA and protein syntheses. Mitosis was not significantly affected by the drug in the cells synchronized with demecolcine (Colcemid). The antibiotic did not interfere with in vitro assembly of tubulin. In the synchronized cells, strong inhibition of DNA synthesis was observed when geldanamycin was introduced into the culture prior to S phase of the cell cycle. The degree of inhibition was stronger with prolongation of incubation period and with increase of DNA synthesis rate. The results suggested that initiation of DNA synthesis or S phase is affected by the drug. DNA degradation was not significantly induced in vivo by the antibiotic. Geldanamycin blocked DNA polymerase α more markedly than β and γ. The degree of inhibition depended upon concentrations of enzyme but not upon those of template, suggesting a drug-enzyme interaction. IC₅₀ for DNA polymerase α was 10μg/ml and for DNA polymerase β 100μg/ml at low concentrations of enzyme. The inhibition of DNA polymerase α by the antibiotic was non-competitive and Ki was 20μM.

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D-Cycloserine showed a decreased lethality against paraquat-treated E. coli than against non-treated cells. E. coli K12 mutants which were deficient in DNA repair were more sensitive than the wild type strain to D-cycloserine. Furthermore, D-cycloserine caused PM2 DNA cleavage in the presence of Fe²⁺, and the cleavage was strongly inhibited by singlet oxygen scavengers. These results indicate that D-cycloserine interacts with DNA and an active oxygen species is involved in the interaction.

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