E. coli mesophilic
plate number (MPN)/g
Samples in
MPN range (n)
Positive
in MPN range
Indicators of Hygiene and
Sanitation
Very often, the term “indicator” is
used to describe a test or organism used
to measure the hygienic conditions of
surfaces in a food production facility be-
Table 1: Salmonella Incidence and E. coli Mesophilic Plate Number in Raw Meat Patties
< 3 270 0.7
3-5 406 4. 9
51-100 54 5. 6
101-240 96 4.1
241-1,100 65 4. 6
1,101-11,000 56 16.1
> 11,000 25 20.0
Adapted from 1
sented data showing a correlation between levels of E. coli and incidence of
Salmonella as an example of this sort of
general correlation, although it is not a
specific lot-to-lot correlation (Table 1). It
should be noted that, although such
index organism tests, where verified, are
not reliable for individual production lots,
they nevertheless point to potential
pathogen issues when viewed over multiple lots. Thus, they have some utility if
correctly interpreted. Their presence
could be used to enhance existing food
safety systems.
This concept provides some of the
justification for the International Commission on Microbiological Specifications for Foods (ICMSF) sampling
schemes as they relate to “indicator” assays (ICMSF Cases 4-6; Figure 14) applied to foods as a measure of risk. The
ICMSF sampling scheme is based upon
risk associated with the product either
from extrinsic (e.g., temperature, pressure treatments, handling, post-process
contamination, etc.) or intrinsic factors
(e.g., pH and water activity) vs. the risk
associated with particular agents (e.g.,
spoilage, indicator, moderate, serious
and severe organisms or toxins, etc.).
• Aerobic plate count
• Psychotropic plate count
• Enterobacteriaceae
• Coliform (defined by method)
• Yeast and mold
• Listeria-like organisms (LLOs)
Generally useful for the following:
• Pre-operational sampling
• Post-operational sampling
• Environmental sampling
• Product/ingredient sanitary
quality (not LLOs)
• Indicator of potential for spoilage
(not LLOs)
fore, during and after operations (see
Table 2). However, different specifications would apply to these conditions.
For example, a pre-operational (
post-san-itization) surface should be free of coliforms, EB, yeast and molds, since these
Table 2: Tradition, Useful Indicators:
Sanitation and Quality
organisms are very sensitive to the action
of sanitizers. Hence, if they are discovered, investigation as to the effectiveness
of soil removal that often entraps and
protects microbes should be undertaken.
However, no facility can be expected to
be maintained under sterile conditions.
Consequently, some APCs, psychrotrophic plate counts and mesophilic
spore counts taken on pre-operational
surfaces can be expected. Good targets
for large (e.g., 1 ft2) pre-operational surfaces are less than 100 or less than 1,000
APCs with less than 10 coliforms or EB
and less than 10 yeast and molds. However, some use different values for different surface areas (e.g., 4× 50 cm2).
Evancho et al.
5, quoting the U.S. Public
Health Service as providing a guide of
less than 100 colonies recovered per
utensil or surface area of equipment
sampled, added that the interpretation
from unmeasured surfaces (e.g., utensils,
gaskets, pump impellors, etc.) should be
based upon historical data gained from
these when sampled after documented
thorough cleaning and sanitization.
Operational and post-operational surfaces can be expected to have higher hygienic indicator counts, particularly on
surfaces that have been in contact with
moist product residues. However, it is
unlikely that sites initially with less than
1,000 colony-forming units (CFUs) per
ft2 will become contaminated with
100,000 or more CFUs by incidental
means (e.g., air or contact with clean
hands, etc.). Such an increase in population is the result of inadequately controlled microbial growth.
4
Figure 1: ICMSF Sampling Plans
Adapted from ICMSF, Volume 2 and found in
4
Truncated pathogen assays as hygienic
indicators
These assays are characterized by
truncating or modifying a standard
pathogen assay to include broader microbial groups that may contain the
pathogen of concern but also indices of
hygiene and product quality. These positive assays are not “presumptive positive”
pathogen assays. The best known example
of this is the test for Listeria-like organisms, wherein the standard assay is
stopped at the Fraser broth or Modified
Oxford medium (MOX) plate steps as in
Figures 2 (secondary enrichment and selective medium steps, respectively), 3
