Differentiation of Escherichia coli and Aerobacter aerogenes by Gas Liquid Chromatography

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Abstract
Some species of coliform organisms were characterized by measuring the volatile materials that they produced during growth in milk. Homogenized-pasteurized milk after being heated to 98[degree]C for 90 min. then vacuum distilled to eliminate volatile materals and reconstituted to its original volume with double distilled sterile water served as the medium for growth of the bacteria. Volatile materials resulting from the growth of these organisms were measured by gas liquid chromatography (GLC). Five isolates identified as A. aerogenes were easily distinguishable from 5 identified as E. coli by ability of the former to produce compounds in the growth medium which yielded 14.5 and 48 min. peaks. Escherichia freundii and E. intermedia both produced a 14.5 min. peak; however, E. freundii did not produce the 48 min. peak and E. intermedia produced only a small 48 min. peak. A Pseudomonas aerogenoides isolate gave a chromatogram similar to that of A. aerogenes, but peak heights were lower at equivalent or higher bacterial counts. One A. aerogene iso-late which was positive for methyl red yielded chromatograms similar to other A. aerogenes except that the 48 min. peak was lower. It was not as low, however, as the one from E. intermedia. Measurement of volatile materials produced during the growth of bacteria in a suitable medium by GLC is suggested as a means of characterizing E. coli and A. aerogenes.