Purpose: To identify metabolic characteristics and differences between Escherichia coli O157 and the big six non-O157 STEC serogroups that can be used to understand their growth requirements.
Methods: Two different strains of each STEC serogroup were evaluated, including: O157, O26, O111, O103, O45, O121, O145, and O121. The phenotype microarray system from Biolog Inc. was used. Each strain was grown overnight in TSB and colonies were isolated on TSA. Microtiter plates were inoculated by preparing cell suspensions using Biolog protocols. Approximately 760 phenotypic attributes were tested including carbon, nitrogen, sulfur, phosphorous, and peptide nitrogen sources, as well as osmolytes.
Results: Selective STEC serogroup growth was found using the following components: D-Saccharic Acid, D-Serine, D-Sorbitol, D-Ribose, L-Rhamnose, Sucrose, Mucic Acid, m-Hydroxy Phenyl Acetic Acid, L-Galactonic Acid-g-Lactone, b-Methyl-D-Glucuronic Acid, L-Sorbose, b-Hydroxy Butyric Acid, and L-Cysteine. Differences among serogroups were found for the various nutritional components tested. In addition, tolerance to stressors by all STEC serogroups was found to be: NaCl <7%, Urea<6%, Sodium lactate <10%, Sodium formate <5%. Some components that inhibited the growth of all serogroups include: D-Aspartic acid, glycogen, inulin, pectin, urea, and histamine, among others. A comprehensive list of substances that favor or limit their growth was created.
Significance: These results will contribute to our understanding of the STEC serogroups, specially their nutritional requirements to further improve enrichment and solid media, develop new media, enhance the ability to isolate strains, and improve the public health.