Fundamental Food Microbiology, Third Edition - Fuad Fathir

INDICATORS OF BACTERIAL PATHOGENS 431
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4. The indicator should be present in the fecal matter in much higher numbers than
the enteric pathogens so they can be easily detected (enumerated or isolated) even
when a food is contaminated with small amounts of fecal matter.
5. The indicator should be detected (enumerated or isolated) and identified within a
short time, easily, and economically, so that a product, following processing, can
be distributed quickly, and several samples from a batch can be tested.
6. The indicator should be detected by using one or more newly developed molecular
biology techniques for rapid identification.
7. The indicator should be detected (enumerated or isolated) even in the presence
of large numbers of associated microorganisms, which can be achieved by using
compounds that inhibit growth of associated microorganisms but not of the indicator.
8. The indicator should have a growth and survival rate in a food as that of the enteric
pathogens. It should not grow slower or die off faster than the pathogens in a
food. If it dies off more rapidly than the pathogen, then, theoretically, a food can
be free of the indicator during storage but can still have pathogens.
9. The indicator should not suffer sublethal injury more (in degree) than the pathogens
do when exposed to physical and chemical stresses. If the indicator is more
susceptible to sublethal stresses, it will not be detected by the selective methods
used in the enumeration, and a food may show no or very low acceptable levels
of the indicator even when the pathogens are present at higher levels.
10. The indicator should preferably be present when the pathogens are present in a
food; conversely, it should be absent when the enteric pathogens are absent. Unless
such correlations exist, the importance of an indicator to indicate the possible
presence of a pathogen in a food reduces greatly.
11. There should preferably be a direct relationship between the level of an indicator
present and the probability of the presence of an enteric pathogen in a food. This
will help set up regulatory standards or specifications for an indicator limit for
the acceptance or rejection of a food for consumption. For this criterion, it is very
important to recognize whether the high numbers of an indicator in a food have
resulted from a high level of initial contamination (and a greater chance for the
presence of a pathogen) or from their growth in the food from a very low initial
contamination (in which case a pathogen may not be present even when the
indicator is present in high numbers).
It is apparent that no single bacterial group or species will be able to meet all the
criteria of an ideal indicator. Several bacterial groups or species satisfy many of
these criteria. The characteristics, advantages, and disadvantages of some of the
important and accepted indicator bacterial groups and species (of enteric pathogens)
are described here. 1–3
A. Coliforms
III. COLIFORM GROUP
In the coliform group, coliforms, fecal coliforms, and Esc. coli are discussed. They
are not separate, as both fecal coliforms (mostly Esc. coli) and Esc. coli belong to