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United States Department of Agriculture

Agricultural Research Service

Research Project: MOLECULAR MECHANISMS OF PATHOGENIC BACTERIA INTERACTIONS WITH PLANT SURFACES AND ENVIRONMENTAL MATRICES

Location: Environmental Microbial and Food Safety Laboratory

Title: Growth inhibition of E. coli O157:H7 by EC869 expressing CDI system

Authors
item Nou, Xiangwu
item Jones, Jonathan -
item Hayes, Christopher -
item Low, David -

Submitted to: BARC Poster Day
Publication Type: Abstract Only
Publication Acceptance Date: March 29, 2013
Publication Date: April 18, 2013
Citation: Nou, X., Jones, J., Hayes, C., Low, D. 2013. Growth inhibition of E. coli O157:H7 by EC869 expressing CDI system. BARC Poster Day.

Technical Abstract: 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 potential toxin coding sequences termed "orphans" that target susceptible bacterial cells through direct cellular contact via CdiA binding. A very few EHEC bacterial strains possess CDI homologous sequences. Genomic analyses indicated E. coli O157:H7 strain EC869 encoded a CDI system with 11 potential toxin orphan coding sequences. The purpose of this study was to examine the functionality of the EC869 CDI system in competing against other E. coli and especially EC O157:H7 strains. EC869 and target strains, including E. coli O157:H7 strain (EDL933), were co-inoculated in 10% TSB in a continuous culturing system. 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. Co-culturing with EC869 resulted in strong growth inhibition of the targeted O157:H7 strain. After 24 hrs 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 hrs 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 2hr 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. 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 can be further explored for reducing O157:H7 from the animal reservoir.

Last Modified: 7/25/2014
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