Environmental Engineering Reference
In-Depth Information
indicator bacteria Types
The most commonly tested fecal bacteria indicators are total coliforms, fecal
coliforms,
Escherichia coli
, fecal streptococci, and enterococci. All but
E. coli
are composed of a number of species of bacteria that share common charac-
teristics, including shape, habitat, or behavior;
E. coli
is a single species in the
fecal coliform group. Total coliforms are widespread in nature. All members
of the total coliform group can occur in human feces, but some can also be
present in animal manure, soil, and submerged wood and in other places
outside the human body. The usefulness of total coliforms as an indicator
of fecal contamination depends on the extent to which the bacteria species
found are fecal and human in origin. For recreational waters, total coliforms
are no longer recommended as an indicator. For drinking water, total coli-
forms are still the standard test, because their presence indicates contamina-
tion of a water supply by an outside source.
Fecal coliforms, a subset of total coliform bacteria, are more fecal specific in
origin; however, even this group contains a genus,
Klebsiella
, with species that
are not necessarily fecal in origin.
Klebsiella
are commonly associated with
textile and pulp and paper mill wastes. If these sources discharge to a local
stream, consideration should be given to monitoring more fecal and human-
specific bacteria. For recreational waters, this group was the primary bacte-
ria indicator until relatively recently, when the USEPA began recommending
E. coli
and enterococci as better indicators of health risk from water contact.
Fecal coliforms are still being used in many states as indicator bacteria.
E. coli
is a species of fecal coliform bacteria specific to fecal material from humans
and other warm-blooded animals. The USEPA recommends
E. coli
as the best
indicator of health risk from water contact in recreational waters; some states
have changed their water quality standards and are monitoring accordingly.
Fecal streptococci generally occur in the digestive systems of humans and
other warm-blooded animals. In the past, fecal streptococci were monitored
together with fecal coliforms, and a ratio of fecal coliforms to streptococci
was calculated. This ratio was used to determine whether the concentra-
tion was of human or nonhuman origin; however, this is no longer recom-
mended as a reliable test.
Enterococcus
spp. are a subgroup within the fecal
Streptococcus
group. Enterococci are distinguished by their ability to survive
in saltwater, and in this respect they more closely mimic many pathogens
than do the other indicators. Enterococci are typically more human specific
than the larger fecal
Streptococcus
group. The USEPA recommends entero-
cocci as the best indicator of health risk in saltwater used for recreation and
as a useful indicator in freshwater, as well.
Which bacteria Should be Monitored?
Which bacteria chosen for testing depends on what is to be determined. Does
swimming in the local stream pose a health risk? Does the local stream meet
state water quality standards? Studies conducted by the USEPA to determine
