Variability in gas production by Escherichia coli in enrichment media and its relationship to pH

Variability in gas production in multiple subcultures of Escherichia coli was assessed in two selective enrichment media and in lactose peptone water. Considerable variability occurred with all media at 37 and 44 degrees C. Addition of buffer increased gas production and decreased variability. The relationships between pH, growth, and gas production were complex. In buffered media, viable counts increased by 269 x 10(6) to 382 x 10(6)/U of pH fall, whereas in unbuffered media, they increased by 9.45 x 10(6) to 30.37 x 10(6)/U of pH fall. In buffered and unbuffered media, pH fell as gas production rose. However, variability in gas production among individual subcultures was not associated with changes in pH.