Use of pulsed-field gel electrophoresis for epidemiological study of Escherichia coli O157:H7 during a food-borne outbreak

Abstract

Food and patient isolates from an Escherichia coli O157:H7 outbreak associated with undercooked ground beef were characterized by pulsed-field gel electrophoresis and Shiga-like toxin genotype. Pulsed-field gel electrophoresis confirmed the epidemiologically implicated source of the two-state outbreak and differentiated between outbreak and sporadic strains. Escherichia coli O157:H7 is an important food-borne pathogen in North America and Europe. Pathogenicity is associated with the production of one or more Shiga-like toxins (SLT-I, SLT-II, or both) (8, 13). Most food-borne outbreaks, as well as sporadic cases of gastrointestinal illness, have been linked epidemiologically to undercooked ground beef (6). Other food and water sources, as well as person-to-person transmission, have also been documented (3, 5, 6, 9, 10). In January 1994, the state health departments of Washington and Oregon began a joint epidemiological investigation of a two-state outbreak of E. coli O157:H7 infections. There were 33 culture-confirmed cases of E. coli O157:H7 infection, with onset from mid-January to mid-March 1994, in the two states. Using a recently improved method (15) for detection of E. coli O157:H7 in food, we analyzed 10 samples of raw or undercooked ground beef collected from the homes of six patients with culture-confirmed E. coli O157:H7 illness. Using SLT gene profiles and pulsed-field gel electrophoresis (PFGE) patterns, we then compared the E. coli O157:H7 strains isolated from the ground beef with isolates obtained from patients by the respective state health laboratories. The purposes of this study were to confirm the epidemiologically implicated source of the two-state E. coli O157:H7 outbreak and to differentiate unrelated sporadic strains from outbreak strains. A total of 39 E. coli O157:H7 strains were analyzed: 26 patient isolates, 12 food-borne isolates from seven positive ground beef samples, and one control strain, EDL 933 (Table 1). The PCR method (15) was used to assess the presence of SLT-I and SLT-II genes in the E. coli O157:H7 isolates. PFGE was performed by modification of the method of Böhm and Karch (4). Briefly, isolates were grown in tryptic soy broth with 0.6% yeast extract at 35ЊC on a rotator to an optical density at 600 nm of 0.8 to 1.0. The cells were washed and resuspended in 1 M NaCl-10 mM Tris-50 mM EDTA, mixed with an equal volume of 1% low-melting-point preparative-grade agarose (Bio-Rad Laboratories, Hercules, Calif.), and dispensed into plug molds (Bio-Rad). After the plugs solidified, they were transferred to tubes that contained 1 mg of lysozyme per ml in 1 M NaCl-6 mM Tris-0.1 M EDTA-0.5% Sarkosyl-0.2% deoxycholate for 1 h at 37ЊC with gentle agitation. The solution was replaced with 1 mg of proteinase K per ml in 0.5 M

Molecular typing of enterohemorrhagic Escherichia coli O157:H7 isolates in Japan by using pulsed-field gel electrophoresis

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Application of PFGE to source tracking of faecal pollution in coastal recreation area: a case study in Aoshima Beach, Japan

“…Pulsed-field gel electrophoresis can be used to compare genotypic characteristics within the same species and is an established standard tracking method for identifying the route of infection in epidemiological studies (Barrett et al 1994;Johnson et al 1995). This method has extremely high sensitivity, reproducibility and discrimination ability compared with other MST methods (Meays et al 2004).…”