Differentiation of Escherichia coli and Aerobacter aerogenes by Gas Liquid Chromatography

Abstract

Six isolates of Aerobacter aerogenes; one Pseudomonas aergenoidcs ; five Escherichia coli; one Escherichia freundii; and one Escherichia intermedia were obtained from different sources and classified according to Bergey's 5(anual. Cultures of each were prepared in heat- and vacuum-treated milk and incubated 30 hr at 35 C. 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 dis- tinetly different head-space gas chromato- graphic patterns. A. acrogenes produced compounds that gave 14.5- and 48-rain peaks. The 14.5-rain peak was isobutyl alcohol and the other was an unidentified carbonyl compound. These compounds were not produced by E. coll. E. freundii produced a 14.5-nfin peak, but not a 48-rain peak. A. aerogenes pro- duced both peaks and E. coli produced neither. The chromatograms of E. inter- media were different from those of E. coli and E. freundii in that a small 48-rain 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-rain peaks produced in spite of a high total count. Characterization of bacteria by chromato- graphic methods was first attempted by Mattick et al. in 1956 (11). Some species of Lactobacil- Zus and Streptococcus were characterized by subjecting the acetic acid extract of bacterial cells to two-dimensional paper chromatography. Later, Cheeseman et al. (7) found that some 73