title: Petite colony formation by Listeria monocytogenes and Listeria species grown on esculin-containing agar.
abstract: Several strains of Listeria species formed petite-sized colonies from parent stock cultures when grown on agar media containing 0.2-1% (w/v) esculin. This was observed in Listeria monocytogenes (7/22 strains), L. innocua (1/3), L. grayi (1/1), L. seeligeri (1/3), and L. welshimeri (1/1), but not in L. ivanovii (0/1) and L. murrayi (0/1). This phenomenon was only observed on agar media that contained esculin. All petite isolates had biotyping profiles identical to their larger, normal-sized counterpart isolates. Normal and petite-sized isolates from two L. monocytogenes strains, Scott A and V7, were pathogenic to immunosuppressed white mice. On media containing 0.5% (w/v) esculin + ferric iron, Listeria cultures produced colony diameters intermediate in size between those of normal and petite cultures. When pregrown in glucose broth, all petite isolates demonstrated visible beta-glucosidase (esculinase) activity within 5 min, while the normal-sized isolates showed beta-glucosidase activity only after at least 20-70 min. This evidence suggests that cells forming petite colonies are beta-glucosidase constitutive variants within the parent population, while cells that form normal-sized colonies are inducible for beta-glucosidase (esculinase) activity. A possible role for the esculin hydrolysis product, esculetin, in causing petite colony formation is discussed.
authors.affiliation: Department of Food Science, University of Arkansas, Fayetteville 72703.
authors.forename: G R
authors.initials: GR
authors.lastname: Siragusa
authors.forename: L A
authors.initials: LA
authors.lastname: Elphingstone
authors.forename: P L
authors.initials: PL
authors.lastname: Wiese
authors.forename: S M
authors.initials: SM
authors.lastname: Haefner
authors.forename: M G
authors.initials: MG
authors.lastname: Johnson
mesh_terms: D000818:Animals; D015373:Bacterial Typing Techniques; D003470:Culture Media; D004929:Esculin / Q000378:metabolism*; D005260:Female; D005290:Ferric Compounds / Q000378:metabolism; D006868:Hydrolysis; D008087:Listeria / Q000201:enzymology / Q000254:growth & development* / Q000472:pathogenicity; D008089:Listeria monocytogenes / Q000201:enzymology / Q000254:growth & development* / Q000472:pathogenicity; D051379:Mice; D014468:Umbelliferones / Q000378:metabolism; D001617:beta-Glucosidase / Q000378:metabolism
chemical_list: D003470:Culture Media; D005290:Ferric Compounds; D014468:Umbelliferones; D004929:Esculin; D001617:beta-Glucosidase; C007628:esculetin