Fig. 18: Enterobacter cloacae Growing on XLD Agar

Acid from fermentation of lactose and/or sucrose lowers the pH and turns the phenol red from red (alkaline) to yellow (acid). In addition, breakdown of the amino acid lysine produces alkaline end products which raises the pH and causes some of the agar to turn a deeper red. No hydrogen sulfide is produced.
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Microbiology Laboratory Manual by Gary E. Kaiser, PhD, Professor of Microbiology
is licensed under a Creative Commons Attribution 4.0 International License.
Last updated: September, 2017