title: Performance comparison of a fliC(h7) real-time PCR assay with an H7 latex agglutination test for confirmation of the H type of Escherichia coli O157:H7.
abstract: Escherichia coli O157:H7 is a foodborne pathogen that causes hemorrhagic colitis and hemolytic uremic syndrome. Positive identification of E. coli O157:H7 is made using biochemical tests and specific antisera or latex agglutination reagents for the O157 and H7 antigens. However, under certain conditions, some E. coli O157:H7 isolates can appear to be nonreactive with H7 antisera and may require multiple passages on motility medium to restore H7 antigenicity. In this study, we compared the performance of a real-time PCR test with that of a method using latex agglutination reagents to detect the presence of the fliC(h7) gene or the H7 antigen, respectively, in E. coli O157:H7 isolates. One hundred twenty-six E. coli strains were tested including reference strains and strains isolated from meat. Lyophilized E. coli O157:H7 isolates were rehydrated and were plated on sheep blood agar without passage on motility medium. All strains were analyzed in parallel by a real-time PCR test targeting the fliC(h7) gene and by a latex agglutination test that detects the H7 antigen. The real-time PCR assay showed 100% agreement with the H7 status reported for reference strains and E. coli O157:H7 meat isolates. The latex agglutination test results agreed with the H7 status reported for the E. coli O157:H7 reference strains and non-O157:H7 strains, except for one, E. coli O117:H7; however, 42% (42 of 100) of the E. coli O157:H7 meat isolates tested negative for the H7 antigen by latex agglutination. The real-time fliC(h7) PCR test can be used to confirm E. coli O157:H7 strains that are not expressing the immunoreactive H7 antigen.
authors.affiliation: U.S. Department of Agriculture, Food Safety and Inspection Service, Outbreak Section of the Eastern Laboratory, 950 College Station Road, Athens, Georgia 30605, USA. neelam.narang@fsis.usda.gov
authors.forename: Neelam
authors.initials: N
authors.lastname: Narang
authors.forename: Pina M
authors.initials: PM
authors.lastname: Fratamico
authors.forename: Glenn
authors.initials: G
authors.lastname: Tillman
authors.forename: Kitty
authors.initials: K
authors.lastname: Pupedis
authors.forename: William C
authors.initials: WC
authors.lastname: Cray
mesh_terms: D000942:Antigens, Bacterial / Q000032:analysis / Q000235:genetics* / Q000276:immunology; D019453:Escherichia coli O157 / Q000145:classification* / Q000235:genetics*; D029968:Escherichia coli Proteins / Q000235:genetics; D005408:Flagellin; D005506:Food Contamination / Q000032:analysis; D007841:Latex Fixation Tests; D016133:Polymerase Chain Reaction / Q000379:methods* / Q000592:standards*; D012680:Sensitivity and Specificity; D013045:Species Specificity
chemical_list: D000942:Antigens, Bacterial; D029968:Escherichia coli Proteins; C516095:FliC protein, E coli; C022863:H antigen; D005408:Flagellin