Chromogenic culture media for the detection of Listeria spp. and the identification of Listeria monocytogenes. Listeria Chromogenic Agar Base according to Ottaviani and Agosti (ALOA) is a selective medium for the presumptive isolation and identification of Listeria monocytogenes and Listeria spp. in food and clinical samples. The X-glucoside chromogenic gives all Listeria species a blue color due to their β-glucosidase enzyme. Other organisms that have that enzyme, like Enterococci, are inhibited by the selective agents. The differential activity is also obtained by lipase C substrate, responsible for the opaque white hallo that surrounds L. monocytogenes.
