Influence of Aeration on Rate of Growth in Cultures

Abstract

DURING a recent investigation, it was necessary to obtain large quantities of coliform organisms free from agar extractives and from complex peptide material. While working with a simple medium containing ammonium salts (or asparagine) and dextrose, it was found that an enormous increase in growth could be obtained by passing air through the medium. The following conditions were found to be essential to the success of this procedure. (1) The aeration had to be violent and unremitting, and sufficient to maintain the whole of the medium in a state of turbulence. (2) Media of a more complex nature, giving a positive biuret reaction, frothed excessively, and the common foam suppressors failed to control it. (3) The cooling effect of such an air stream was considerable, and immersion of the culture bottle in a water-bath was necessary to overcome this. A practical method of dealing with it in an incubator could not be found. (4) A moderately complex system of air sterilization was unavoidable. (5) Carbon and nitrogen in the medium had to be adjusted to meet the increased growth.