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At least 541 records · Page 30Linked to original sources
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↗
PubMed1964

TRANSFER OF EPISOMIC ELEMENTS TO PROTEUS. I. TRANSFER OF F-LINKED CHROMOSOMAL DETERMINANTS.

Falkow, Stanley (Walter Reed Army Institute of Research, Washington, D.C.), J. A. Wohlhieter, R. V. Citarella, and L. S. Baron. Transfer of episomic elements to Proteus. I. Transfer of F-linked chromosomal determinants. J. Bacteriol. 87:209-219. 1964.-F-linked lac(+) genes may be transferred from Escherichia coli to several species of Proteus by conjugation. Usually the transferred genetic elements are markedly unstable in Proteus, but repeated plating permits the selection of relatively stable Proteus lac(+) strains. Proteus strains carrying F-linked lac(+) markers are heterogenotes and limited donors for lac(+). In addition, both the fertility and lac(+) property may be eliminated from Proteus by treatment with acridine orange. Escherichia and Proteus possess very different overall deoxyribonucleic acid (DNA) base compositions. In CsCl density gradients of DNA extracted from Proteus lac(+) strains, the acquisition of Escherichia genes by Proteus may be correlated with the addition of a physically recognizable high molecular weight, native DNA fraction of Escherichia base composition. Proteus lac(+) strains synthesize a beta-galactosidase which is indistinguishable from E. coli enzyme by several criteria. Despite this specificity, the regulatory functions of Escherichia lac(+) genes appear to be impaired in Proteus.

Acridines↗
PubMed1964

GENETIC CONTROL OF RESTRICTION AND MODIFICATION IN ESCHERICHIA COLI.

Boyer, Herbert (Yale University, New Haven, Conn.). Genetic control of restriction and modification in Escherichia coli. J. Bacteriol. 88:1652-1660. 1964.-Bacterial crosses with K-12 strains of Escherichia coli as Hfr donors (Hfr Hayes, Hfr Cavalli, and Hfr P4X-6) and B/r strains of E. coli as F(-) recipients were found to differ from crosses between K-12 Hfr donors and K-12 F(-) recipients in two ways: (i) recombinants (leu, pro, lac, and gal) did not appear at discrete time intervals but did appear simultaneously 30 min after matings were initiated, and (ii) the linkage of unselected markers to selected markers was reduced. Integration of a genetic region linked to the threonine locus of K-12 into the B/r genome resulted in a hybrid which no longer gave anomalous results in conjugation experiments. A similar region of the B strain was introduced into the K-12 strain, which then behaved as a typical B F(-) recipient. These observations are interpreted as the manifestation of host-controlled modification and restriction on the E. coli chromosome. This was verified by experiments on the restriction and modification of the bacteriophage lambda, F-lac, F-gal, and sex-factor, F(1). It was found that the genetic region that controlled the mating responses of the K-12 and B/r strains also controlled the modification and restriction properties of these two strains. The genes responsible for the restricting and modifying properties of the K-12 and B strains of E. coli were found to be allelic, linked to each other, and linked to the threonine locus.

Amino Acids↗
PubMed1965

PREPARATION AND PROPERTIES OF A VI ANTIGEN-DEGRADING ENZYME.

Baker, Edgar E. (Boston University School of Medicine, Boston, Mass.), and Roberta E. Whiteside. Preparation and properties of a Vi antigen-degrading enzyme. J. Bacteriol. 89:1217-1224. 1965.-Vi antigen can be hydrolyzed by an inducible enzyme produced by a microorganism isolated from soil. The organism can be identified as Bacillus sphaericus. The enzyme in the culture supernatant fluid can be concentrated and partially purified by precipitation with ammonium sulfate at 50% of saturation. The partially purified enzyme is relatively stable. Incubation of the enzyme with Vi antigen causes a rapid loss of serological activity, a decrease in viscosity, the loss of ability to precipitate albumin at pH 4.0, and the production of reducing sugar and hexosamine. Optimal conditions for enzyme action on Vi antigen are pH 8.4 and 40 C. The reaction rate is independent of the substrate concentration. Intact protein and calcium activates the Vi antigen-enzyme system. The enzyme is not inhibited by its reaction products.

Bacillus↗
PubMed1962

Resistance of Salmonella typhi to chloramphenicol. I. A preliminary report.

Resistance of Salmonella typhi to chloramphenicol has not been reported so far except in strains made resistant in the laboratory. While examining 52 smooth strains of S. typhi and three smooth strains of S. paratyphi A 10 strains of S. typhi were found to be resistant to 50 to 500 mug. chloramphenicol. Of these 10 strains, eight appeared to be tolerant of the antibiotic, but the remaining two strains appeared to produce a substance that antagonizes or destroys chloramphenicol.

Anti-Bacterial Agents↗