Fecal Coliforms in Antarctica

Bacteria are everywhere—on our skin, in our food, suspended in our drinking water. Although the microbial majority is benign, a few bacterial species can make us sick. To safeguard against food- and water-borne disease, microbiologists routinely screen our drinking water for bacterial pathogens.

Animal feces contain coliform bacteria, microorganisms that inhabit the intestines of warm-blooded animals. Many coliform bacteria are also found on plants and in soil and water. Coliform bacteria are not pathogens themselves, but their presence indicates the possibility of finding pathogens. In contrast, fecal coliform bacteria such as Escherichia coli are found in feces, and their presence in drinking water indicates fecal contamination. E. coli can also be a pathogen itself, so if E. coli is found in drinking water there is a good chance that other pathogens are present, too.¹

To detect E. coli and other coliform bacteria, microbiologists filter water samples and place the filter in a Petri dish containing growth medium such as Endo agar. Microorganisms from the water grow and form colonies, giving an estimate of the number of bacteria in each milliliter of water.

While E. coli forms colored, shiny colonies on Endo agar, other coliforms grow as white or clear colonies.

Dark colonies = E. coli White/clear colonies = coliform bacteria White + Dark colonies = total coliform bacteria

The guidelines of maximum allowable limits for total coliforms in drinking and recreational waters vary by state. Representative limits appear in the table below.^2,3,4

Questions

1. Why would we want to count the number of fecal coliforms in a water sample?
2. Do 400 coliforms per 100 milliliters strike you as very many?
3. How many other types of bacteria might be present in a normal water sample?
4. What problems might Sally encounter when she uses these techniques in Antarctica?

References

1. “Membrane Filter Method for the Simultaneous Detection of Total Coliforma and E. coli in Drinking Water,” EPA 600-R00-013, http://www.epa.gov/nerlcwww/MI_emmc.pdf. [An EPA publication that describes the background and experimental protocol for a membrane filter fecal coliform detection method.]
2. “The Subcommittee on Water Resources and Environment Hearing on H.R. 3673, The Recreational Waters Protection Act,” http://www.house.gov/transportation/water/05-01-02/05-01-02memo.html. [One resource suggesting a federal law governing minimum acceptable limits for fecal coliform contamination.]
3. “The Estimation of Bacterial Biomass in Mediterranean Seawater,” C. M. Turley, K. Børsheim, J. Iriberri and J. Prosser. Formerly available at http://www.cetiis.fr/mtp/qaps/BACFINL.html. [An estimate of total bacterial counts in Mediterranean seawater.]
4. “Public Health Tests Available to Wisconsin Citizens,” http://www.slh.wisc.edu/ehd/citizens.html. [The fecal coliform and E. coli acceptable limits for swimming beaches from the State of Wisconsin.]

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