Extended phage-typing scheme for Escherichia coli O157:H7

Area of Science:

• Microbiology
• Infectious Diseases
• Food Safety

Background:

• Significant increase in human isolates of verotoxigenic (VT + ve) Escherichia coli O157:H7 in Canada between 1982 and 1989.
• These infections are linked to diarrheal cases, hemolytic uremic syndrome, and hemorrhagic colitis.

Purpose of the Study:

• To characterize the phage types of VT + ve E. coli O157:H7 strains isolated in Canada and internationally.
• To investigate the epidemiological patterns and potential transmission routes of E. coli O157:H7.

Main Methods:

• Phage typing of 3273 VT + ve E. coli O157:H7 strains, including 3255 from Canada and 18 from other countries.
• Extension of the phage typing scheme from 14 to 62 distinct phage types.
• Analysis of phage type distribution in human isolates, non-human sources (meat, slaughterhouses), and outbreak-associated strains.

Main Results:

• Thirty-five different phage types were identified in Canada, with nine types (1, 2, 4, 8, 14, 21, 23, 31, 32) accounting for over 1% of human cases.
• The same nine predominant phage types were found in non-human sources, indicating a likely foodborne transmission route for most human cases.
• Phage types 1, 4, 8, 31, and 14 were the most frequent, showing regional variations in occurrence.

Conclusions:

• The study identified key phage types of E. coli O157:H7 prevalent in Canada, with a strong association between human and foodborne isolates.
• The findings suggest that foodborne transmission is the primary route for most human infections caused by VT + ve E. coli O157:H7 in Canada.
• Monitoring phage type distribution is crucial for understanding and controlling E. coli O157:H7 outbreaks.