Growth studies on the lactic streptococci: IV. Some observations on redox potential
Summary Redox potential changes at 30°C in anaerobic reconstituted skim-milk cultures of Streptococcus cremoris AM1 and AM2 and Streptococcus lactis ML8 have been investigated in batch cultures and continuous cultures maintained at constant pH by the addition of fresh medium. Str. lactis ML8 was more strongly reducing than either Str. cremoris AM1 or AM2. The positive Eh values which can arise in dense continuous cultures of lactic streptococci are not likely to affect either the lactic acid formation or proteolytic activity of the resultant bacterial concentrate. An electrolytic reduction cell is described which allows variations in redox potential in cultures to be controlled simply and effectively.
Growth studies on the lactic streptococci: II. The effect of agitation on the growth characteristics of Streptococcus lactis ML8 in batch culture
Summary Investigations on the growth characteristics of Streptococcus lactis ML8 in skim-milk medium have indicated that agitation of the medium may decrease the growth rate of the organism by decreasing the availability of CO2 (CO2 effect) and of soluble nitrogen (soluble nitrogen effect). The former effect was observed only when the CO2 concentration was depleted by heat sterilization; the latter occurred when a certain threshold level of agitation was exceeded. Results suggested that the soluble nitrogen affect was caused by an alteration in the rate of diffusion of substances formed in the immediate vicinity of the bacterial cell by the proteolytic enzyme system.
VIRULENCE ENHANCEMENT OF A FILAMENTOUS STRAIN OF CANDIDA ALBICANS AFTER GROWTH ON MEDIA CONTAINING CYSTEINE
During the course of a metabolic study of various strains of Candida albicans, it was noted that a definite inhibition of the fungus occurred, when cysteine in concentrations ranging from 0.04 per cent to 1.0 per cent was added to a glucose-glycine-yeast extract medium. In low concentrations (below 0.25 per cent), the inhibition was of a fungistatic nature. Although measureable turbidimetric growth appeared after one week, in the medium containing 0.25 per cent cysteine this growth was significantly less than growth in the similar medium without cysteine. However, one of the strains produced a large amount of filamentous growth within 48 hours. This strain was essentially avirulent, though it fulfilled all other criteria for C. albicans. The virulent strains maintained normal yeastlike growth for at least seven days before the appearance of observable filamentation. When the avirulent variety was grown on Sabouraud's glucose agar or glucose-glycine-yeast extract agar to which cysteine-free base had been added (0.25 per cent concentration), there was a suppression of the filamentous rough growth and an enhancement of the normal smooth yeastlike growth. This is in line with the observation of Nickerson and Chung (Am. J. Botany, 41,114120, 1954). The virulence of the colonies obtained from the cysteine medium was studied. For this purpose 0.25 ml of a standardized suspension of organisms from these colonies, grown for 48 hours at 37 C and containing approximately 1 X 105 cells, was inoculated intravenously into Barckmann IS-32 white Swiss mice of both sexes, average weight, 25.0 g. For the sake of TABLE 1 Pathogenicity of strains of Candida albicans