Indicators of Food Microbial Quality and Safety
479
some reports indicate that some bacterial pathogens are more resistant in water. It is not, however, as
resistant as intestinal viruses. Buttiaux and Mossel
11 concluded that various pathogens may persist
after E. coli is destroyed in foods that are frozen, refrigerated, or irradiated. Similarly, pathogens may
persist in treated waters after E. coli destruction. Only in acid food does E. coli have a particular value
as an indicator organism due to its relative resistance to a low pH.
11
Detection and Enumeration
A large number of methods have been developed for the detection and enumeration of E. coli and
coliforms, and some are discussed in Chapters 10 and 11. One of the standard references listed in
Table 10–1 should be consulted for an appropriate method to use under specified conditions.
Distribution
The primary habitat of E. coli is the intestinal tract of most warm-blooded animals, although sometimes
it is absent from the gut of hogs. The primary habitat of E. aerogenes is vegetation and, occasionally,
the intestinal tract. It is not difficult to demonstrate the presence of coliforms in air and dust, on the
hands, and in and on many foods. The issue is not simply the presence of coliforms but their relative
numbers. For example, most market vegetables harbor small numbers of lactose-fermenting, Gramnegative rods of the coliform type, but if these products have been harvested and handled properly,
the numbers tend to be quite low and of no real significance from the standpoint of public health.
Coliform Criteria and Standards
Although the presence of large numbers of coliforms and E. coli in foods is highly undesirable, it would
be virtually impossible to eliminate all from fresh and frozen foods. The basic questions regarding
numbers are as follows:
1. Under proper conditions of harvesting, handling, storage, and transport of foods by use of a
hazard analysis critical control point (HACCP) system, what is the lowest possible and feasible
number of coliforms to maintain?
2. At what quantitative level do coliforms or E. coli indicate that a product is unsafe?
In the case of water and dairy products, there is a long history of safety related to allowable coliform
numbers. Some coliform and E. coli criteria and standards for water, dairy products, and other foods
covered by some regulatory agencies are as follows:
1. not over 10/ml for Grade A pasteurized milk and milk products, including cultured products
2. not over 10/ml for certified raw milk and not over 1 for certified pasteurized milk
3. not over 10/ml for precooked and partially cooked frozen foods
4. not over 100/ml for crabmeat
5. not over 100/ml for custard-filled items
Low numbers of coliforms are permitted in sensitive foods at numbers ranging from 1 to not over
100/g or 100 ml. These criteria reflect both feasibility and safety parameters.
Some products for which coliform criteria have been recommended by the International Commission on the Microbiological Specifications for Foods (ICMSF)
38 are listed in Table 20–4. The
479
some reports indicate that some bacterial pathogens are more resistant in water. It is not, however, as
resistant as intestinal viruses. Buttiaux and Mossel
11 concluded that various pathogens may persist
after E. coli is destroyed in foods that are frozen, refrigerated, or irradiated. Similarly, pathogens may
persist in treated waters after E. coli destruction. Only in acid food does E. coli have a particular value
as an indicator organism due to its relative resistance to a low pH.
11
Detection and Enumeration
A large number of methods have been developed for the detection and enumeration of E. coli and
coliforms, and some are discussed in Chapters 10 and 11. One of the standard references listed in
Table 10–1 should be consulted for an appropriate method to use under specified conditions.
Distribution
The primary habitat of E. coli is the intestinal tract of most warm-blooded animals, although sometimes
it is absent from the gut of hogs. The primary habitat of E. aerogenes is vegetation and, occasionally,
the intestinal tract. It is not difficult to demonstrate the presence of coliforms in air and dust, on the
hands, and in and on many foods. The issue is not simply the presence of coliforms but their relative
numbers. For example, most market vegetables harbor small numbers of lactose-fermenting, Gramnegative rods of the coliform type, but if these products have been harvested and handled properly,
the numbers tend to be quite low and of no real significance from the standpoint of public health.
Coliform Criteria and Standards
Although the presence of large numbers of coliforms and E. coli in foods is highly undesirable, it would
be virtually impossible to eliminate all from fresh and frozen foods. The basic questions regarding
numbers are as follows:
1. Under proper conditions of harvesting, handling, storage, and transport of foods by use of a
hazard analysis critical control point (HACCP) system, what is the lowest possible and feasible
number of coliforms to maintain?
2. At what quantitative level do coliforms or E. coli indicate that a product is unsafe?
In the case of water and dairy products, there is a long history of safety related to allowable coliform
numbers. Some coliform and E. coli criteria and standards for water, dairy products, and other foods
covered by some regulatory agencies are as follows:
1. not over 10/ml for Grade A pasteurized milk and milk products, including cultured products
2. not over 10/ml for certified raw milk and not over 1 for certified pasteurized milk
3. not over 10/ml for precooked and partially cooked frozen foods
4. not over 100/ml for crabmeat
5. not over 100/ml for custard-filled items
Low numbers of coliforms are permitted in sensitive foods at numbers ranging from 1 to not over
100/g or 100 ml. These criteria reflect both feasibility and safety parameters.
Some products for which coliform criteria have been recommended by the International Commission on the Microbiological Specifications for Foods (ICMSF)
38 are listed in Table 20–4. The