Relation between Food Concentration and Surface for Bacterial Growth

Abstract

The effect of low concentrations of dextrose and peptone on the numbers of Escherichia coli with and without glass beads was studied. E. coli failed to grow in the medium containing 0.5 and 2.5 ppm. dextrose and peptone. The addition of glass beads to the medium at these concs. permitted a considerable growth of this organism. The increase in growth of E. coli due to the addition of glass beads was noticeable up to a conc. of 25 ppm. of dextrose and peptone. Beyond this conc. the numbers with and without beads were practically the same. The bact. population of stream water is increased by (1) addition of clean sand, (2) agitation (3) aeration. The addition of slime covered stones obtained from river bottom to surface waters resulted in an increase in the numbers of the bacteria in the water. The magnitude of the increase was less than without the addition of such stones. Inert surfaces such as glass beads, clean sand and stones evidently enable bacteria to develop in substrates otherwise too dilute for growth. As a result these surfaces become covered with an active biological slime increasing the rate of biol. reaction and decreasing the numbers of bacteria in the supernatant water. Thus the addition of clean surfaces tends to increase the numbers of bacteria in dilute media and the addition of surfaces covered with biol. slime tends to decrease the numbers of bacteria.