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At least 397 records · Page 22Linked to original sources
PubMed1964

MITOMYCINS AND PORFIROMYCIN: CHEMICAL MECHANISM OF ACTIVATION AND CROSS-LINKING OF DNA.

Mitomycins and porfiromycin, generally nonreactive in the natural oxidized state, behave as bifunctional "alkylating" agents upon chemical or enzymatic reduction, followed by spontaneous loss of the tertiary methoxy (hydroxyl) group and formation of an aromatic indole system. Thus activated, mitomycins and porfiromycin react in vitro with purified DNA, linking its complementary strands. A high content of guanine and cytosine favors this cross-linking reaction, which is the basis of the lethal effect in vivo of these antibiotics. The activation and cross-linking reactions are discussed in terms of reactive sites on the mitomycin and DNA molecules.

Anti-Bacterial Agents↗
PubMed1964

STIMULATION OF CAROTENOGENESIS BY MICROBIAL CELLS.

Spent mycelia of Blakeslea trispora recovered from a previous fermentation enhanced carotene production by mated cultures of the same organism. Peak yields of 107 to 142 mg of carotene per 100 ml of medium were achieved in 6 days. beta-Carotene constituted 92% of the total carotenoids produced. The enhancing substance was found present in an aqueous extract of the mycelium. Part of its activity was due to an organic acid fraction. Other microbial cells, molds, yeasts, and bacteria were also capable of enhancing carotene production.

Bacillus cereus↗
PubMed1965

MICROMETHOD (SPOT-PLATE) DETERMINATION OF IN VITRO ANTIBIOTIC SUSCEPTIBILITY.

The spot-plate method for determining in vitro antibiotic susceptibility is a modified version of the standard tube dilution technique, with the same principle of twofold dilution. Results of the spot-plate method are compared with those of the standard tube dilution technique. It is proposed that the spot-plate method is an equally accurate, but more rapid and economical, technique for determining in vitro antibiotic susceptibility.

Anti-Bacterial Agents↗
PubMed1965

EFFECT OF NATURALLY OCCURRING XANTHINES ON BACTERIA. I. ANTIMICROBIAL ACTION AND POTENTIATING EFFECT ON ANTIBIOTIC SPECTRA.

The effect of xanthines on various microorganisms was studied. The antibacterial effect was not high; most of the test organisms could easily withstand a concentration of 2,500 mug/ml. Caffeine was more antibacterial than theophylline, and the latter more than theobromine. Caffeine citrate exhibited greater inhibitory effect than did pure caffeine. The effect was both bacteriostatic and bactericidal against susceptible organisms. The susceptibility of organisms to xanthines differed greatly even in related species. The morphology of Aerobacter aerogenes and A. cloacae was affected under the influence of caffeine; filamentation of cells followed sublethal doses. Potentiation was seen with antibiotics and caffeine; resistant strains were killed with a lower dose of drug in the presence of caffeine. This potentiating effect was pronounced with the tetracyclines; with streptomycin, the effect was the contrary.

Anti-Bacterial Agents↗
PubMed1965

DIVERSIFICATIONS IN THE TUBE DILUTION TEST FOR ANTIBIOTIC SENSITIVITY OF MICROORGANISMS.

The tube dilution method of performing antibiotic sensitivity tests is commonly employed as an accurate method for defining the minimal inhibitory concentration in relation to pathogenic organisms. It is also used as a reference for comparing minimal inhibitory concentrations with the size of the zone of inhibition in the agar diffusion test. Although surveys have shown that there is no standardized method and technique of performing the tube dilution test, it is generally assumed that all of the diversified methods will yield the same results and interpretations. With the assistance of five experts, seven different tube dilution methods were compared; 16 antibiotics, and three organisms for each antibiotic, were used. The conclusions drawn are that, although the accuracy of a single method within its own confines is acknowledged, the minimal inhibitory concentrations and interpretations cannot be interpolated from one laboratory to another where a different technique is employed. The results are frequently discrepant. It is suggested that a uniform method be developed and promulgated for general use.

Anti-Bacterial Agents↗
PubMed1963

ANTIMICROBIAL ACTION OF NITROGEN-CONTAINING STEROIDS.

Smith, Rodney F. (University of Maryland, Baltimore), Donald E. Shay, and Norman J. Doorenbos. Antimicrobial action of nitrogen-containing steroids. J. Bacteriol. 85:1295-1299. 1963.-A new group of 16 synthetic nitrogen-containing steroids have been tested against a variety of microorganisms for antimicrobial properties. The gradient plate screening method, serial dilution, and dry weight techniques were used in the studies. The organisms tested consisted of 14 gram-negative bacteria, 10 gram-positive bacteria, 2 actinomycetes, 7 yeasts, and 8 molds. Inhibitory properties were found to be specific and potent in four compounds, with inhibitory concentrations as low as 0.37 mug/ml. Three of the active steroids are 4-aza cholestanes and one is a 4-nor-3,5-secocholestane amide. Sensitivity to the compounds was greatest in the gram-positive bacteria, followed by the yeasts and molds. The gram-negative bacteria were not inhibited. All 16 steroids interfered to some extent with pigmentation in Serratia marcescens but not with pigment production in Pseudomonas aeruginosa. In a few instances, some of the molds were stimulated by the steroids at a concentration of 250 mug/ml.

Actinomycetales↗
PubMed1963

SURVEY OF THE BACTERIOCINES OF ENTEROCOCCI.

Brock, Thomas D. (Indiana University, Bloomington), Barbara Peacher, and Deborah Pierson. A survey of the bacteriocines of enterococci. J. Bacteriol. 86:702-707. 1963.-A survey has been made of bacteriocine production by a wide variety of well-characterized strains of group D streptococci. On the basis of spectrums and sensitivity to chloroform, heat, and proteolytic enzymes, five distinct bacteriocines can be defined. Type 1 is produced by all Streptococcus zymogenes (S. faecalis var. zymogenes) strains, is active against a wide variety of gram-positive bacteria, and is also a hemolysin. Type 2 is produced by some S. liquefaciens (S. faecalis var. liquefaciens) strains, and acts on many enterococci as well as on certain other lactic acid bacteria. Type 3 is produced by certain strains of both S. faecalis and S. faecium, and inhibits a wide variety of group D streptococci, but is inactive against all other lactic acid bacteria tested except Leuconostoc citrovorum. Type 4 is produced by certain S. faecium strains and resembles in certain ways the type 3 activity, but differs from it in other ways. Type 5 has been found to be produced by only one proteolytic strain of S. zymogenes, and this bacteriocine has a very narrow spectrum. The strain that produces this bacteriocine also produces type 1 activity. No strain is sensitive to a bacteriocine of the type it produces.

Bacillus cereus↗