Fundamental Food Microbiology, Third Edition - Fuad Fathir

INDICATORS OF BACTERIAL PATHOGENS 433
B. Fecal Coliforms
1. 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 ± 0.2 or 45.0 ± 0.2�C) for 24 h in selective broths containing
lactose. Lactose fermentation, with the production of gas, is considered a presumptive
positive test. 1,7
2. 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 due to 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
C. Escherichia coli
1. 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 other coliforms by the indole production
from tryptone, methyl red reduction due to acid production (red coloration), Voges
Proskauer reaction (production of acetyl-methyl carbinol from glucose) and citrate
utilization as a C-source (IMViC) reaction patterns. Esc. coli Type I and Type II
give IMViC reaction patterns, respectively, of + + – – and – + – –. The – + – –
reaction pattern of Esc. coli Type II could also be due to slow or low production of
indole from tryptone (or peptone). The IMViC tests are conducted with an isolate
obtained after testing a food sample for coliform group or fecal coliform group.
However, there is a concern now about the adequacy of these reaction patterns to
identify Esc. coli types.
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