508 Modern Food Microbiology
that is applied in a food establishment at a point during or after processing to monitor hygiene (it, too,
may include nonpathogens). Before recommending a criterion, the ICMSF
8 notes that each product
must be in international trade, must have associated with it good epidemiological evidence that it has
been implicated in foodborne disease, and have associated with it good evidence that a criterion will
reduce the potential hazard(s) in Principle 2.
The Codex definition of a microbiological criterion consists of five components: (1) a statement of the
organisms of concern and/or their toxins, (2) the analytical methods for their detection and quantitation,
(3) a sampling plan, including when and where samples are to be taken, (4) microbiological limits
considered appropriate to the food, and (5) the number of sample units that should conform to these
limits. These five components are embodied in a sampling plan.
Sampling Plans
A sampling plan is a statement of the criteria of acceptance applied to a lot based on appropriate
examinations of a required number of sample units by specified methods. It consists of a sampling
procedure and decision criteria and may be a two-class or a three-class plan.
A two-class plan consists of the following specifications: n, c, m; a three-class plan requires n, c,
m, and M, where
n = the number of sample units (packages, beef patties, and so forth) from a lot that must be
examined to satisfy a given sampling plan.
c = the maximum acceptable number, or the maximum allowable number of sample units that may
exceed the microbiological criterion m. When this number is exceeded, the lot is rejected.
m = the maximum number or level of relevant bacteria per gram; values above this level are either
marginally acceptable or unacceptable. It is used to separate acceptable from unacceptable
foods in a two-class plan, or, in a three-class plan, to separate good quality from marginally
acceptable quality foods. The level of the organism in question that is acceptable and attainable
in the food product is m. In the presence/absence situations for two-class plans, it is common
to assign m = 0. For three-class plans, m is usually some nonzero value.
M = a quantity that is used to separate marginally acceptable quality from unacceptable quality
foods. It is used only in three-class plans. Values at or above M in any sample are unacceptable
relative to health hazard, sanitary indicators, or spoilage potential.
A two-class plan is the simpler of the two and in its simplest form may be used to accept or reject a
larger batch (lot) of food in a presence/absence decision by a plan such as n = 5, c = 0, where n = 5
means that five individual units of the lot will be examined microbiologically for, say, the presence
of salmonellae, and c = 0 means that all five units must be free of the organisms by the method of
examination in order for the lot to be acceptable. If any unit is positive for salmonellae, the entire lot
is rejected. If it is desired that two of the five samples may contain coliforms, in a presence/absence
test, for example, the sampling plan would be n = 5, c = 2. By this plan, if three or more of the fiveunit samples contained coliforms, the entire lot would be rejected. Although the presence/absence
situations generally obtained for salmonellae, an allowable upper limit for indicator organisms such
as coliforms is more often the case. If it is desired to allow up to 100 coliforms/g in two of the five
units, the sampling plan would be n = 5, c = 2, m = 10
2 . After the five units have been examined
for coliforms, the lot is acceptable if no more than two of the five contain as many as 10
2 coliforms/g
but is rejected if three or more of the five contain 10
2 coliforms/g. This particular sampling plan may
that is applied in a food establishment at a point during or after processing to monitor hygiene (it, too,
may include nonpathogens). Before recommending a criterion, the ICMSF
8 notes that each product
must be in international trade, must have associated with it good epidemiological evidence that it has
been implicated in foodborne disease, and have associated with it good evidence that a criterion will
reduce the potential hazard(s) in Principle 2.
The Codex definition of a microbiological criterion consists of five components: (1) a statement of the
organisms of concern and/or their toxins, (2) the analytical methods for their detection and quantitation,
(3) a sampling plan, including when and where samples are to be taken, (4) microbiological limits
considered appropriate to the food, and (5) the number of sample units that should conform to these
limits. These five components are embodied in a sampling plan.
Sampling Plans
A sampling plan is a statement of the criteria of acceptance applied to a lot based on appropriate
examinations of a required number of sample units by specified methods. It consists of a sampling
procedure and decision criteria and may be a two-class or a three-class plan.
A two-class plan consists of the following specifications: n, c, m; a three-class plan requires n, c,
m, and M, where
n = the number of sample units (packages, beef patties, and so forth) from a lot that must be
examined to satisfy a given sampling plan.
c = the maximum acceptable number, or the maximum allowable number of sample units that may
exceed the microbiological criterion m. When this number is exceeded, the lot is rejected.
m = the maximum number or level of relevant bacteria per gram; values above this level are either
marginally acceptable or unacceptable. It is used to separate acceptable from unacceptable
foods in a two-class plan, or, in a three-class plan, to separate good quality from marginally
acceptable quality foods. The level of the organism in question that is acceptable and attainable
in the food product is m. In the presence/absence situations for two-class plans, it is common
to assign m = 0. For three-class plans, m is usually some nonzero value.
M = a quantity that is used to separate marginally acceptable quality from unacceptable quality
foods. It is used only in three-class plans. Values at or above M in any sample are unacceptable
relative to health hazard, sanitary indicators, or spoilage potential.
A two-class plan is the simpler of the two and in its simplest form may be used to accept or reject a
larger batch (lot) of food in a presence/absence decision by a plan such as n = 5, c = 0, where n = 5
means that five individual units of the lot will be examined microbiologically for, say, the presence
of salmonellae, and c = 0 means that all five units must be free of the organisms by the method of
examination in order for the lot to be acceptable. If any unit is positive for salmonellae, the entire lot
is rejected. If it is desired that two of the five samples may contain coliforms, in a presence/absence
test, for example, the sampling plan would be n = 5, c = 2. By this plan, if three or more of the fiveunit samples contained coliforms, the entire lot would be rejected. Although the presence/absence
situations generally obtained for salmonellae, an allowable upper limit for indicator organisms such
as coliforms is more often the case. If it is desired to allow up to 100 coliforms/g in two of the five
units, the sampling plan would be n = 5, c = 2, m = 10
2 . After the five units have been examined
for coliforms, the lot is acceptable if no more than two of the five contain as many as 10
2 coliforms/g
but is rejected if three or more of the five contain 10
2 coliforms/g. This particular sampling plan may