TO YOUR HEALTH:
Studying bacteria growth in drinking water
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From left: Professor
Gregory Harrington, Pathobiological Sciences Professor Michael
Collins, State Lab of Hygiene Advanced Microbiologist Becky Hoffmann,
CEE PhD student Andy Jacque, and Pathobiological Sciences Research
Associate Alice Yuroff and Senior Scientist Becky Manning.
(View larger image)
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 n Professor Gregory
Harrington’s lab, water samples swish gently through tabletop
vessels in a way that mimics fluid flow through a pipe. The samples
aren’t just ordinary water: They comprise special mixtures of
sanitized water and a group of disease-causing organisms called Mycobacterium
avium complex, or MAC.
Researchers have found MAC in public water-distribution systems, as
well as in household plumbing and drinking water. “There are a
number of different places where you find it, but water heaters are
a good example of a place where it might be found,” says Harrington.
Despite the presence of MAC in such locations, the number of human infections
from the bacteria likely is low and is limited primarily to immuno-compromised
people. In fact, the U.S. Centers for Disease Control and Prevention
lists the incidence of disease caused by the bacteria as not reportable,
and some population data suggest a disease rate of just one in 100,000
annually.
Previous studies have focused on detecting MAC and
determining the quantity of the bacteria present in water-distribution
systems, says Harrington. “They’ve probably been there,
but we’ve just started to develop the detection methods to find
them,” he says. “Now that we seem to know that they’re
there, we need to figure out what to do about them.”
For that, researchers must learn what MAC like—or dislike. In
controlled laboratory studies, funded via a grant through the UW-Madison
Vilas Trust, Harrington hopes to learn about the conditions under which
Mycobacteria thrive.
In addition, he is working in collaboration with colleagues in the UW-Madison
School of Veterinary Medicine and the Wisconsin State Laboratory of
Hygiene. With three-year funding from the American Water Works Association
Research Foundation, that group is developing improved methods for detecting
MAC, not just in specially concocted laboratory samples—but in
the environment. “We want to make sure that we can find the Mycobacteria
in water under a variety of conditions, like different piping materials
or different disinfectants,” says Harrington.
One challenge the group is attempting to overcome is that MAC grow very
slowly compared with other bacteria. For example, in the traditional
bacteria plate-counting method, researchers collect a water sample and
put it on an agar plate to grow. Researchers can count most bacteria
within a couple of days, up to a week, says Harrington. “With
mycobacteria, you’ve got to wait six to eight weeks before you
can count,” he says.
One of his collaborators, Professor of Pathobiological Sciences Michael
Collins, is an expert in bovine MAC research and has developed methods
to speed its analysis time from nearly two months to just under two
weeks. “Our objective as engineers is to figure out how to control
it; his objective is to figure out how to look for it,” says Harrington.
Harrington’s Vilas award enables him to conduct research beyond
the scope of the group project. He is studying the role such factors
as water temperature, chlorine content and piping materials play in
MAC presence in the water supply.
Each of his tabletop vessels, or biofilm reactors, is filled with MAC-spiked
water in a varying concentration and temperature. As these water samples
circulate in a reactor, Harrington and graduate student Andy Jacque
study whether the bacteria grow in the water, and whether they grow
on tiny copper, cast iron or PVC “coupons.” “Bacteria
have the potential to either grow on the surface of those materials
in what we would call a biofilm, or they have the potential to grow
in the water itself,” says Harrington.
Though he is conducting initial tests with sterilized, MAC-spiked water,
Harrington eventually will repeat his research on unsterilized water
without added MAC. “This will allow us to assess the presence
of MAC species in the water supply and the ability of these species
to colonize the reactors at concentrations typical of drinking-water
systems,” he says.
In the future, Harrington hopes his research will contribute to systems
that eliminate MAC from the water supply. “If we can determine
what conditions favor their absence, then maybe we can come up with
engineering designs that prevent their occurrence in water,” he
says.
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