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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.

When the protocol that we had used to demonstrate a single division of bacterial cells in airborne particles was changed to one that increased the glycerol content of the atomizer fluid from 1 to 5% (vol/vol), thus producing larger particles, more than two (and nearly three) divisions of bacteria occurred within 6 h of aerosol time.

Effect of 3% hydrogen peroxide on the viability of Serratia marcescens. J. Bacteriol. 91:925-929. 1966.-Populations of Serratia marcescens were exposed to 3% H202 at temperatures from 0 to 20 C. The reaction appeared to follow an Arrhenius plot, but variable numbers of diminutive colonies were found after cell numbers started to decrease. Colony numbers varied on different sampling media and increased when additional incubation was imposed. The overall reaction was sensitive to age of culture, and growth capabilities of treated samples varied with time of treatment, especially during times when no loss of viability was noted. Catalase activity per cell did not correlate with changes in sensitivity; iron added to growth medium increased catalase activity and decreased sensitivity, but not in the same manner. Although the fundamental reaction is presumably molecular in nature, present methods of viability assay measure more than single events and are not suitable for these studies. One end product of metabolism in aerobic bacteria is presumed to be hydrogen peroxide (4), which the cell could convert to water by the action of catalase; in high concentrations, however, H202 is bactericidal. The mechanism of disinfectant action is not known, but excess amounts of H202 are believed to oxidize some vital internal cell constituent (6). Cellular catalase could protect cells by destroying external H202. Initially, we sought information on the thermodynamics of the disinfectant reaction. We investigated the influence of temperature, iron in the growth medium, culture age, and catalase activity on the disinfectant action of 3 % hydrogen peroxide. We conclude that the overall reaction does not conform to simple kinetic theory. MATERIALS AND METHODS Serratia marcescens, strain 8UK, was grown at 31 C in a chemically defined medium described by Dimmick (2). A 1-ml amount of a sterile solution of ferric ammonium citrate containing 1 mg/ml of iron was sometimes added per liter of growth medium. Data shown in Fig. 1, 2, and 3 were obtained when "house" distilled water from a block-tin still was used. The water was stored in a stainless-steel tank and was delivered through plastic pipe with stainless-steel valves. Data in the remaining figures were obtained with use of water redistilled in a Corning AG-2 all-glass unit. Unless noted, samples of a single, third-passage 925 Vol. 91, No. 3