PubMed Health⌕ Search

Biomedical subjects

F T Robb

Publications and source records attributed to F T Robb.

47 records · Page 3Linked to original sources
PubMed1980

Rifampin and bacteriocin resistance in Bacteroides fragilis.

A low-molecular-weight bacteriocin produced by a Bacteroides fragilis strain inhibited ribonucleic acid polymerase activity in crude extracts of a susceptible B. fragilis indicator strain. A total of 10 rifampin-resistant mutants of the indicator strain were isolated. Nine of the rifampin-resistant mutants were resistant to the bacteriocin, and the other mutant was hypersusceptible. The rifampin- and bacteriocin-resistant mutants all adsorbed approximately the same amount of the bacteriocin as the indicator strain. Two of these rifampin- and bacteriocin-resistant mutants were investigated further, and the polymerase activity in crude extracts of the two mutants was not affected by either rifampin or the bacteriocin. The in vitro ribonucleic acid polymerase activity of the hypersusceptible strain was more susceptible to the bacteriocin than the parent indicator strain was. The bacteriocin-producing strain was susceptible to rifampin but was resistant to its own bacteriocin in vivo. The in vitro ribonucleic acid polymerase activity of the producer strain was only slightly affected by 64 arbitrary units of the bacteriocin. Increasing concentrations of the bacteriocin inhibited ribonucleic acid polymerase extracts of the producer strain.

Bacteriocins↗
PubMed1980

Peptone induction and rifampin-insensitive collagenase production by Vibrio alginolyticus.

Vibrio alginolyticus produces an extracellular collagenase which requires specific induction by collagen or its high-molecular-weight fragments. Peptone also induces collagenase during the late exponential and early stationary growth phases. The peptone inducers have been shown to have a broad molecular weight range between 1,000 and 60,000. The peptone inducers supported slow growth of V. alginolyticus when supplied as the sole nitrogen source in minimal medium. Digestion of the peptone inducers with purified V. alginolyticus collagenase resulted in a decrease in their inducing ability, whereas digestion with trypsin or alpha-chymotrypsin did not. This indicated that induction by the inducers required the presence of collagenase-sensitive bonds. Prolonged digestion of the inducers with collagenase did not completely eliminate the inducing ability of the inducers. The peptone inducers acted as inhibitors of collagenase. A minimal medium induction system has been developed which involves resuspending cells at high density in a medium containing succinate, (NH(4))(2)SO(4), KH(2)PO(4), and the peptone inducer. Cells grown in minimal medium induce earlier than cells grown on peptone, Casamino Acids, or tryptone. Collagenase production was shown to occur for 30 to 60 min in the presence of rifampin at levels which completely inhibit the incorporation of [(3)H]uracil into trichloroacetic acid-precipitable material. Chloramphenicol completely and immediately abolished collagenase production, which together with labeling studies has confirmed that collagenase production involves de novo synthesis of the enzyme. Both glucose and Casamino Acids repressed collagenase production, although synthesis of the enzyme continued for 30 to 60 min after their addition. The repression of collagenase production by glucose and Casamino Acids was more severe than the inhibition of enzyme formation due to addition of rifampin.

Amino Acids↗
PubMed1979

Characterization and mode of action of a bacteriocin produced by a Bacteroides fragilis strain.

A Bacteroides fragilis strain produces a low-molecular-weight (13,500 to 18,700), proteinaceous bacteriocin during the stationary growth phase. The extracellular bacteriocin is not inducible by ultraviolet light or mitomycin C and is stable between pH 7.5 and 8.2. The majority of the bacteriocin is thermolabile, but a small proportion (3%) of the bacteriocin is stable after autoclaving at 121 degrees C for 15 min. Killing of sensitive bacteroides cells follows single-hit kinetics, and the interaction of a single molecule of bacteriocin with a target cell occurs in two stages. The killing of susceptible cells is affected by temperature and the growth state of the susceptible cells. The bacteriocin is unusual in that the primary event in its mode of action is the inhibition of RNA synthesis. The bacteriocin inhibits RNA synthesis immediately but has no effect on DNA synthesis or intracellular ATP levels. Protein synthesis is inhibited after a delay of 20 min, presumably as a result of the initial inhibition of RNA synthesis.

Adenosine Triphosphate↗
PubMed1979

Bacteriocin production by Clostridium acetobutylicum in an industrial fermentation process.

High titers of a noninducible bacteriocin were produced by Clostridium acetobutylicum in a molasses fermentation medium used for the industrial production of solvents. Release of the bacteriocin towards the end of the exponential growth phase was accompanied by lysis of the culture and inhibition of the production of solvents. The producer cells were sensitive to the bacteriocin, which only affected other C. acetobutylicum strains and a Clostridium felsineum strain. The thermolabile bacteriocin was not inactivated by protease enzymes and had no optimum stability between pH 4 and 5. The sedimentation coefficient of the bacteriocin was 6S.

Bacteriocins↗
PubMed1978

Phage growth characteristics on stationary phase Achromobacter cells.

The growth characteristics of alpha3a bacteriophage on stationary phase Achromobacter strain 14 are described. Phage alpha3a growth on stationary phase cells is characterized by a long and variable latent period of 6 to 9 h and an increased burst size of 710 p.f.u./cell as compared with 153 p.f.u./cell in exponential wild type cells. During the latent period the infected cells are very sensitive to changes in growth conditions and in particular, dilution. Pre-conditioning of the bacterial cells by allowing them to stand for 24 h after shaking for 3 days is an important aspect of the stationary phase phage growth system. Cells which have been allowed to stand retain the ability to be infected and to support phage growth for at least 16 days. Shaking cultures gradually lose the ability to support phage growth but the phage can persist in the host cell for 10 days until removal from shaking when the lytic cycle can proceed after allowing the cultures to stand.

Adsorption↗
PubMed1977

Rifampicin-resistant mutant supporting bacteriophage growth on stationary phase Achromobacter cells.

A rifampicin-resistant Achromobacter mutant with an altered RNA polymerase was isolated. The mutant supports phage alpha3a growth in both log and stationary phase cells. Phage growth on stationary phase cells is sensitive to aeration and growth only occurs at oxygen concentrations of less than 5-2 p.p.m. The rifampicin-resistant mutant is similar to the spontaneous mutant strain 14 reported by Woods (1976) in that both mutants support stationary-phase phage growth under micro-aerophilic conditions. The isolation of the rifampicin-resistant mutant with an altered RNA polymerase suggests that the phenomenon of stationary phase phage growth could be due to a change in the template specificity of the Achromobacter RNA polymerase. Plaque morphology mutants which grow on log and/or stationary phase cells of the Achromobacter wild type, strain 14 and rifampicin-resistant strains are also described.

Alcaligenes↗