The Aerogenic Response of Escherichia coli and Strains of Aerobacter in EC Broth and Selected Sugar Broths at Elevated Temperatures

Abstract

Gas formation by 116 strains of Escherichia coli and 104 strains of Aerobacter was determined in a specially constructed and accurately controlled water bath employing EC, lactose, maltose, sucrose, glucose, levulose, and galactose broths at temperatures ranging from 44.5 to 46.5 C. Greatest gas activity occurred in EC broth. In the range 44.9 to 45.5 C over 92% of the E. coli cultures formed gas, but the Aerobacter strains dropped from 68 to 2%. A natural point of separation of the two groups occurred at 45.5 C. Inhibition of the gas-forming mechanism rather than death is the universal response of the Escherichia organisms to these temperatures. The inhibition increases with rising temperatures and is readily reversible. At 46.5 C, 64.5% of all the Escherichia cultures were inhibited and 69.1% of all the cultures were actually viable. In EC broth it was found that as a group atypical E. coli (-+--) were the most resistant gas-positive types. Least resistant in EC broth was a group of known typical fecal isolates of E. coli (++--). Of intermediate resistance between the two groups was the large body of typical E. coli (++--) organisms. Certain individual strains of E. coli excelled in the production of gas in the variety of sugar broths tested at elevated temperatures. The Aerobacter strains did not exhibit this property. Finally it is suggested that elevated temperature incubation studies of this type be conducted in critically controlled water baths with an ascertained accuracy in the vicinity of 45.5 ± 0.1 C under full load.