P2-19 Phenotypic Features of Shiga Toxin-producing Escherichia coli (STEC) Serogroups Based on Metabolism

Tuesday, August 5, 2014
Exhibit Hall D (Indiana Convention Center)
Alexandra Calle, Texas Tech University, Lubbock, TX
Mindy Brashears, Texas Tech University, Lubbock, TX
Guy H. Loneragan, Texas Tech University, Lubbock, TX
Introduction: Current techniques for detection of STEC are mostly based on serological and molecular features. However, isolation is not always as successful as detecting them.  There is not enough knowledge with regards to the specific nutritional requirements or selective agents in media that may affect the growth of the different STEC serogroups. Therefore an investigation into effective cultural techniques for the seven regulated STEC serogroups is needed. 

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.