Enumeration of Coliforms, Faecal Coliforms and of Escherichia Coli in Foods using the MPN Method

HPB Method MFHPB-19
April 2002

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Health products and food branch

Ottawa

Enumeration of coliforms, faecal coliforms and of E. Coli in foods using the mpn method

Donna Christensen
Calgary Laboratory
Canadian Food Inspection Agency
3650 36 St. N.W.
Calgary, AB T2L 2L1

christensend@inspection.gc.ca

Carol Crawford
Burnaby Laboratory
Canadian Food Inspection Agency
3155 Willingdon Green
Burnaby, BC V5G 4P2

crawfordc@inspection.gc.ca

Rick Szabo
Microbiology Research Division
Bureau of Microbial Hazards
HPFB, Food Directorate
Postal Locator 2204A2
Ottawa, ON K1A 0L2

Rick_Szabo@hc-sc.gc.ca

1. Application

The Most Probable Number (MPN) method is applicable to the enumeration of coliforms, faecal coliforms and aerogenic Escherichia coli in foods, food ingredients and water, including contact water from food manufacturing plants, to determine compliance with the requirements of Sections 4 and 7 of the Food and Drugs Act, the Meat Inspection Act, the Canadian Agricultural Products Act and the Fish Inspection Act. Where an Official Method for certain products is specified, that method shall be followed. This revised method replaces MFHPB-19 dated June 2001.

Note: This method is not intended to be used to isolate and enumerate E. coli serotypes associated with human illness, particularly the enterohemorrhagic serotype O157:H7. Many of the pathogenic serotypes do not give a positive faecal coliform reaction and therefore would not be detected and recovered by this method.

2. Description

The MPN procedure involves a multiple tube fermentation technique where three or more decimal dilutions of the sample are inoculated into tubes of broth medium and incubated at a specific temperature and for a specific time. The method is progressive; i.e., first determining the presence of coliforms in the tubes, then determining if these tubes also contain faecal coliforms, and then confirming whether E. coli is present. Based on the number of tubes indicating the presence / absence of the three groups of organisms, the most probable number present can be estimated from a standard statistical MPN table. The method has been shown to produce satisfactory results with naturally-contaminated foods and water for the detection of coliforms, faecal coliforms and aerogenic E. coli (See references 8.1 - 8.5).