Differentiation of Escherichia coli and Aerobacter aerogenes by Gas Liquid Chromatography

Six isolates of Aerobacter aerogenes; one Pseudomonas aergenoides; five Escherichia coli; one Escherichia freundii; and one Escherichia intermedia were obtained from different sources and classified according to Bergey's Manual. Cultures of each were prepared in heat- and vacuum-treated milk and incubated 30 hr at 35C. An attempt was made to differentiate these species by gas chromatography (GLC) of the volatile compounds produced during growth. E. coli and A. aerogenes gave distinctly different head-space gas chromatographic patterns. A. aerogenes produced compounds that gave 14.5- and 48-min peaks. The 14.5-min peak was isobutyl alcohol and the other was an unidentified carbonyl compound. These compounds were not produced by E. coli. E. freundii produced a 14.5-min peak, but not a 48-min peak. A. aerogenes produced both peaks and E. coli produced neither. The chromatograms of E. intermedia were different from those of E. coli and E. freundii in that a small 48-min peak occurred with E. coli in spite of a high total count. P. aerogenoides was distinguished easily from E. coli and E. freundii, but not from E. intermedia by these characteristics. P. aerogenoides could be differentiated from A. aerogenes only by the small size of 10.5-, 14.5-, and 48-min peaks produced in spite of a high total count.