Carbohydrate Utilization by Bacteria Without Evident Acid Production

Abstract

There has been developing recently an increasing realization that bacteria may utilize carbohydrates without an increase in hydrogen-ion concentration. We have undertaken to determine the extent of this type of carbohydrate utilization by examining a number of microorganisms representative of a wide range of bacterial groups, testing each organism in those sugars in which it showed no acid according to the usual indicator method. A series of sugars was added to (1) sugar free beef infusion broth and (2) 2% peptone 0.5% sodium chloride solution as basic mediums, to make 0.4% solutions of the monosaccharides and 0.8% of the disaccharides. The organisms were grown in these sugar mediums at 37°C. for 2-3 weeks (lactose for 3 months, also) and then the mediums were analyzed quantitatively for sugar by a copper reduction method. 1 In most cases, when the use of sugar was apparent only by quantitative analysis, the experiment was repeated and the hydrogen ion concentration determined daily. In doubtful instances, the experiment was repeated in these mediums buffered with phosphates.

Table I shows the sugars employed and those organisms with which the utilization of sugar was always accompanied by evident acid production. Table II shows those organisms which utilized one or more sugars according to quantitative analysis while concurrently the medium increased in alkalinity. In such instances, subcultures to the appropriate carbohydrate indicator agar plates failed to exhibit acid production, except regularly with Sarcina lutea in maltose, and irregularly with B. pyocyaneus in xylose. There were no manifest evidences of colonial dissociation. The sucrose, mannitol, indol, negative B. dysenteriae Shiga cultures were the only ones to show a decrease in pH (a rather sudden drop to about pH 6.0 after remaining at about 6.8 for 10-15 days).