Page Banner

United States Department of Agriculture

Agricultural Research Service

Research Project: Molecular Biology of Human Pathogens Associated with Food

Location: Produce Safety and Microbiology Research

Title: Detection of Shiga toxin variants, virulence genes and the relationship to cytotoxicity in Shiga toxin-producing Escherichia coli (STEC) from domestic farm animals

Authors
item Amezquita-Lopez, Bianca -
item Quiñones, Beatriz
item Leon-Felix, Joshefina -
item Castro-Del Campo, Nohelia -
item Martinez, Celida -
item Chaidez, Cristobal -

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: March 26, 2013
Publication Date: N/A

Technical Abstract: Shiga toxin-producing Escherichia coli (STEC) can cause foodborne illnesses ranging from diarrhea to life-threating diseases such as hemorrhagic colitis, and hemolytic uremic syndrome in humans. In this study, we determined virulence genes, stx subtypes and we evaluated the cytotoxicity in STEC strains isolated from domestic farm animal feces. The STEC strains were analyzed by using PCR with sequence-specific primers to determine the presence of genes encoding intimin (eae), enterohemolysin (ehxA), serine protease (espP), catalase peroxidase (katP), the type II secretion system (etpD), subtilase cytotoxin (subA), autoagglutinating adhesion (saa), type III secreted effectors encoded in the genomic islands OI-122 (ent/espL2), Ol-71 (nleH1-2 and nleA) and the distinct variants of Shiga toxin (stx1a, stx1c, stx1d, stx2a, stx2b, stx2c, stx2d, stx2e, stx2f, stx2g). Also, we evaluated the cytotoxicity the STEC strains by use of a fluoresecent Vero cell-based method. Most (97%) of the 61 strains carried a stx2 gene. Moreover, the stx2a subtype, which is related with severe illness, was present in 10 % in our STEC strains. The other stx subtypes identified were stx1a, stx1c, stx2b, stx2c and stx2d. A total of 25 (46%) of the strains showed more than one stx subtype in its genome, and among them the most frequent combination was stx1a, stx1c, stx2b. The virulence gene most frequently detected was ehxA with 93% (57/61). Other virulence genes such as espP, katP and etpD were more associated with the serotype O157:H7. Only 5 strains of the serotype O8:H19 were positive for the virulence genes saa and subA, which are located in the plasmid pO113. The cytotoxicity was higher in the non-O157 STEC strains with serotypes O8:H19, O73:NT, O111:H8, O146:H8, O146:H21 and ONT:NT. Moreover, the stx subtypes related to high cytotoxicity were stx1a/stx1c/stx2b with a 69.6%, then stx1a/stx2a/stx2c with the 21.8%, and 4.3% for stx1a/stx2b and stx1a subtypes. The STEC strains analyzed from domestic farm animals were found to be diverse in their genetic composition and showed different virulence genes. Furthermore, the presence of more than one stx gene variant in the same isolate reflected a higher cytotoxicity in mammalian cells.

Last Modified: 4/16/2014
Footer Content Back to Top of Page