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P1-122 Contact Dependent Growth Inhibition of Escherichia coli O157:H7 by EC869 CDI System

Monday, July 29, 2013
Exhibit Hall (Charlotte Convention Center)
Xiangwu Nou, U.S. Department of Agriculture-ARS, Beltsville, MD
Jonathan Jones, Roosevelt High School, Greenbelt, MD
Christopher Hayes, University of California-Santa Barbara, Santa Barbara, CA
David Low, University of California-Santa Barbara, Santa Barbara, CA
Introduction: Contact Dependent Growth Inhibition (CDI) is a recently discovered mechanism that microorganisms use to compete in various microecosystems.  CDI systems express large cell surface exposed CdiA proteins with potent antimicrobial peptide tips.  Many CDI systems also contain additional downstream orphan toxins targeting susceptible bacterial cells through direct cellular contact via CdiA binding. Genomic analyses indicated Escherichia coli O157:H7 strain EC869 encoded a CDI system with 11 potential orphan toxin sequences.

Purpose: In this study we examine the functionality of the EC869 CDI system in competing against other O157:H7 strains.

Methods: EC869 and target O157:H7 strain (EDL933) were co-inoculated in 10% TSB in a continuous culturing system with a volume deplacement rate of 30%/h. Both EC869 and the target strain were enumerated daily by plating to determine the growth in the mixed culture. A K12 strain expressing a plasmid-encoded CdiA chimera with the EC869 orphan 11 toxic tip was examined similarly.

Results: Co-culturing with EC869 resulted in strong growth inhibition of the targeted O157:H7 strain. After 24 h of co-culturing, the presentation of the targeted O157:H7 in the mixed culture was reduced from 50% to 11%, and to less than 2% after 48 h incubation. Similar inhibition of growth was observed when a K12 strains was targeted. E. coli K12 strain carrying the cloned chimera CDI system strongly inhibited the growth of K12 target strains, reducing the growth of K12 target strain by more than 3 log units after 2 h exposure. However, no inhibition to the growth of O157:H7 target strain was observed, suggesting different orphan peptides may be required for the growth inhibition of O157:H7.

Significance: The CDI system of EC869 confers the host strain significant advantage in competition with other microorganisms, including other E. coli O157:H7 strains. The CDI system could be further explored for "curing" O157:H7 from the animal reservoir.

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