Abstract
Abstract Pathogenic biotypes of E. coli have been incriminated in food-borne illness. Sensitivity to elevated temperature and atypical behavior precluded assessment of their incidence. A tentative recovery procedure involves direct streak, preenrichment in MacConkey broth at 35°C and transfer to lauryl tryptose broth with incubation at 44°C, and pre-enrichment in nutrient broth at 35°C and transfer to enteric enrichment broth with incubation at 41.5°C. Serological examination of enrichment simplifies analysis. Levine's eosin methylene blue agar is recommended for rapid lactose fermenters; MacConkey's agar should be used for slow fermenters. Primary screening reactions include H2S, arabinose, urease, o-nitrophenyl-β-D-galactosidase, and indole. Secondary reactions comprise lysine decarboxylase, Voges-Proskauer (at 22°C), and other tests required to differentiate E. coli from Citrobacter diver sus, C. freundii, Enterobacter hafniae, Klebsiella pneumoniae, and Shigella species. Slide and tube agglutination reactions are necessary for identification of somatic and capsular antigens. Enhancement of motility by serial passage in a semisolid medium is essential for recognition of flagellar antigen. Confirmatory reactions include nitrate reduction, cytochrome oxidase, and Gram stain. Potentiality for quantitation, applicability to animal pathogens, and ecological samples are discussed.
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