GENOMIC CLASSIFICATION OF CLINICAL ESCHERICHIA COLI O157:H7 STRAINS IN THE STATE OF PENNSYLVANIA
Open Access
- Author:
- Hartzell, Annette Lynn
- Area of Honors:
- Food Science
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Edward G Dudley, Thesis Supervisor
Edward G Dudley, Thesis Supervisor
Gregory Ray Ziegler, Thesis Honors Advisor - Keywords:
- Lineage Specific Polymorphism Assay
E. coli O157:H7
foodborne illness
molecular subtyping
LSPA - Abstract:
- ABSTRACT Objective The purpose of this study was to examine populations of E. coli O157:H7 in Pennsylvania using a DNA-based method. E. coli O157:H7 is a highly virulent foodborne pathogen, and is an organism of interest for food producers, food safety specialists, and researchers. There are two main lineages of E. coli O157:H7, termed Lineage I and Lineage II, which differ in their virulence capacity. Lineage I strains are more frequently implicated in cases of human disease than are Lineage II strains. A third group, termed Lineage I/II, may represent a subset of E. coli O157:H7 with increased virulence potential. Methodology E. coli O157:H7 lineages can be differentiated by DNA based methods. One of these methods, termed the Lineage Specific Polymorphism Assay (LSPA), uses PCR and gel electrophoresis to identify size differences in 6 loci in the bacterial DNA. Based upon the size differences of these 6 regions, lineage types can be assigned. In this study, LSPA was used to determine the lineages of 52 E. coli O157:H7 strains isolated from patients in Pennsylvania during 2007 and 2008. The strains were obtained from the Pennsylvania Department of Health. Six sets of primers were designed to flank lineage-specific polymorphisms, and PCR was used to amplify these regions. Polyacrylamide gel electrophoresis was used to view the products. Bands from the test strains were compared to those of control LSPA type 111111 (Lineage 1) and 222222 (Lineage 2) strains. Test strain bands which matched those of the LSPA 111111 control were given a designation of “1”, and those which matched the bands of the LSPA 222222 control were given a designation of “2”. Test strain bands matching neither Lineage I nor Lineage II bands were given a designation of “3”. Lineage I/II strains were identified as having the LSPA type 211111. Results Of the 52 strains, 63% were found to be Lineage I, 4% were Lineage II, 31% were Lineage I/II, and 2% were LSPA type 311111. Significance and Implications These findings were compared to those from studies on clinical E. coli O157:H7 isolates from other parts of North America. Some differences were found, indicating that there are regional differences in the distribution of E. coli O157:H7 lineages. However, high levels of Lineage I/II strains were found in both Pennsylvania and Michigan, indicating that this virulent strain is may be widespread in North America. This study supports a new model of E. coli O157:H7 virulence, indicating that there are two separate lineages, Lineage I and I/II, which have the capacity to cause serious disease in humans.