Biomedical subjects

R L DIMMICK

Publications and source records attributed to R L DIMMICK.

9 recordsLinked to original sources

PubMed1965

RHYTHMIC RESPONSE OF SERRATIA MARCESCENS TO ELEVATED TEMPERATURE.

Dimmick, Robert L. (University of California, Berkeley). Rhythmic response of Serratia marcescens to elevated temperature. J. Bacteriol. 89:791-798. 1965.-Populations of Serratia marcescens of varied ages and pretreatments, which had been grown in a chemically defined medium, were subjected to thermal stress at 50 to 56 C. The numbers of survivors were plotted vs. time to form survivor curves, and the curves were assembled to form three-dimensional models. The manner in which survivors varied as a function of age and time of heating was variable and often rhythmic. Different three-dimensional patterns were found when different inoculum for the test culture was used. Apparently some "dead" cells again produced colonies after extended heating periods (recuperation); this tendency varied with the age of the culture. Diminutive colony forms, which produced normal colonies upon transfer, appeared and disappeared during heating; this tendency fluctuated with age. It is suggested that survivor curves represent a distribution of resistant forms within the population, and that this distribution varies in a manner best described in terms of servomechanistic response within each cell and within a given culture. Difficulties of attempting to relate changes in specific molecular species to subsequent whole-cell responses are discussed.

Hot Temperature↗

PubMed1964

ATTACHMENT AND GROWTH OF BACTERIA ON SURFACES OF CONTINUOUS-CULTURE VESSELS.

Don H. Larsen (Brigham Young University, Provo, Utah), and R. L. Dimmick. Attachment and growth of bacteria on surfaces of continuous-culture vessels. J. Bacteriol. 88:1380-1387. 1964.-Initial attempts to induce synchrony in a continuous culture of Serratia marcescens by alternating growth temperatures produced fluctuations in the population of a magnitude and at a density higher than predicted by theory. Without temperature change, the density in the 14-ml volume changed with dilution rate, but the total output of cells per hour remained constant, even at dilution rates greater than critical. When glass wool was added to the culture vessel, the total output per hour increased 30-fold. Nonlethal ultrasonic agitation applied to the vessel reduced the population density in continuous culture under both a static and a cyclic temperature program. The decrease in population density, when the washout rate was momentarily increased about tenfold, was less than theoretically predicted, and the subsequent rapid rise, when flow was terminated, indicated the presence of a reservoir of cells on the walls of the vessel continually discharging their progeny into the medium. Several genera were examined in the latter manner; it is estimated that in some cases as many as 90% (S. marcescens, Escherichia coli), and in others (Bacillus spp.) possibly none, of the cells in suspension arose from wall inhabitants. Growth of bacteria on the walls of continuous-culture vessels can significantly influence the population density and, hence, the kinetics of continuous growth.

Bacillus↗

PubMed1963

FREE RADICAL FORMATION AND SURVIVAL OF LYOPHILIZED MICROORGANISMS.

Heckly, Robert J. (University of California, Berkeley), R. L. Dimmick, and J. J. Windle. Free radical formation and survival of lyophilized microorganisms. J. Bacteriol. 85:961-966. 1963.-A correlation between death and spontaneous free radical production, measured by an increase in the relative electron paramagnetic resonance (EPR) signal, was shown to exist for several species of microorganisms stored in the freezedried state, but the relationship between the free radical concentration and number of dead cells was not a simple proportion. Lactose added to Sarcina lutea reduced radical production and increased stability when dry preparations were stored in air. Death and free radical formation were more extensive when lyophilized Streptococcus lactis cultures were stored in air than in vacuum. Free radicals were also produced by dry yeast. Few, if any, free radicals were produced by bacteria or yeast stored in vacuum. It was shown that the observed free radical production was not caused by exposure to light. The EPR signal produced by dry Serratia marcescens decreased rapidly when cells were exposed to a humid atmosphere but the EPR signal slowly increased after cells were redried and exposed to oxygen.

Bacteria↗

PubMed1961