426 ◾ Fundamental Food Microbiology
considered post-heat-treatment contamination from improper sanitation. In heat-processed foods,
their presence (even in small numbers) is viewed with caution. Thus, in heat-processed foods, their
specificity as an indicator is considered favorably (more as an indicator of improper sanitation
than fecal contamination). Several selective media have been recommended to determine coliform
numbers in food samples. These are selective-differential media, and they differ greatly in their
recovery ability of coliforms (Chapter 42). The results are based on the ability of most coliforms to
ferment lactose and produce gas and are available in one to two days. The presence of sublethally
stressed or injured cells can considerably reduce the recovery in selective media. Several other
factors, such as high temperature of melted agar media in pour plating, high acidity of a food,
and presence of lysozymes (egg-based products) in a food, can further reduce the enumeration of
stressed cells. Modified detection methods have been developed to recover injured coliforms (see
Chapters 10 and 42). Even with some disadvantages, coliforms are probably the most useful and
most extensively used indicators. 1,4–7
Fecal Coliforms
Organisms and Sources
Fecal coliform bacteria also constitute a group of bacteria and include those coliforms whose specificity as fecal contaminants is much higher than that of coliforms. This group includes mostly Esc.
coli, along with some Klebsiella and Enterobacter spp. Nonfecal coliforms are eliminated by using
a high incubation temperature (44.5°C ± 0.2°C or 45.0°C ± 0.2°C) for 24 hours in selective broths
containing lactose. Lactose fermentation, with the production of gas, is considered a presumptive
positive test. 1,7
Occurrence and Significance in Food
Some fecal coliforms are present in raw foods of animal origin. They can be present in plant foods
from contaminated soil and water. High numbers can be a result of either gross contamination
or growth from a low initial level, probably because of improper storage temperature. Their presence in heat-processed (pasteurized) foods is probably because of improper sanitation after heat
treatment.
In raw foods that are to be given heat treatment, their presence, even in high numbers (~10 3 /g
or mL) is not viewed gravely; if the numbers go higher, some importance is given to contamination of fecal matter, improper sanitation, and possible presence of enteric pathogens. A need for
corrective measures becomes important. In contrast, in heated products and ready-to-eat products
(even raw), their presence, especially above a certain level, is viewed cautiously for possible fecal
contamination and presence of enteric pathogens. A food can be accepted or rejected based on the
numbers present. This group is extensively used as an indicator in foods of marine origin (shellfish)
and in water and wastewater. 1,7
escherichia coli
Organisms and Sources
In contrast to either coliforms or fecal coliforms, Esc. coli has a taxonomic basis. 1 It includes only
the Escherichia spp. of the coliform and fecal coliform groups. Esc. coli strains conform to the
general characteristics described for coliform groups. Biochemically, they are differentiated from
considered post-heat-treatment contamination from improper sanitation. In heat-processed foods,
their presence (even in small numbers) is viewed with caution. Thus, in heat-processed foods, their
specificity as an indicator is considered favorably (more as an indicator of improper sanitation
than fecal contamination). Several selective media have been recommended to determine coliform
numbers in food samples. These are selective-differential media, and they differ greatly in their
recovery ability of coliforms (Chapter 42). The results are based on the ability of most coliforms to
ferment lactose and produce gas and are available in one to two days. The presence of sublethally
stressed or injured cells can considerably reduce the recovery in selective media. Several other
factors, such as high temperature of melted agar media in pour plating, high acidity of a food,
and presence of lysozymes (egg-based products) in a food, can further reduce the enumeration of
stressed cells. Modified detection methods have been developed to recover injured coliforms (see
Chapters 10 and 42). Even with some disadvantages, coliforms are probably the most useful and
most extensively used indicators. 1,4–7
Fecal Coliforms
Organisms and Sources
Fecal coliform bacteria also constitute a group of bacteria and include those coliforms whose specificity as fecal contaminants is much higher than that of coliforms. This group includes mostly Esc.
coli, along with some Klebsiella and Enterobacter spp. Nonfecal coliforms are eliminated by using
a high incubation temperature (44.5°C ± 0.2°C or 45.0°C ± 0.2°C) for 24 hours in selective broths
containing lactose. Lactose fermentation, with the production of gas, is considered a presumptive
positive test. 1,7
Occurrence and Significance in Food
Some fecal coliforms are present in raw foods of animal origin. They can be present in plant foods
from contaminated soil and water. High numbers can be a result of either gross contamination
or growth from a low initial level, probably because of improper storage temperature. Their presence in heat-processed (pasteurized) foods is probably because of improper sanitation after heat
treatment.
In raw foods that are to be given heat treatment, their presence, even in high numbers (~10 3 /g
or mL) is not viewed gravely; if the numbers go higher, some importance is given to contamination of fecal matter, improper sanitation, and possible presence of enteric pathogens. A need for
corrective measures becomes important. In contrast, in heated products and ready-to-eat products
(even raw), their presence, especially above a certain level, is viewed cautiously for possible fecal
contamination and presence of enteric pathogens. A food can be accepted or rejected based on the
numbers present. This group is extensively used as an indicator in foods of marine origin (shellfish)
and in water and wastewater. 1,7
escherichia coli
Organisms and Sources
In contrast to either coliforms or fecal coliforms, Esc. coli has a taxonomic basis. 1 It includes only
the Escherichia spp. of the coliform and fecal coliform groups. Esc. coli strains conform to the
general characteristics described for coliform groups. Biochemically, they are differentiated from