Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Water quality

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are able to use the pollutant compound as a food source. In

contrast, some forms of microbial growth can detrimental to

products being produced or dangerous to the health of people

consuming the water. Ensuring the quality of water from a

microbiological standpoint is thus of extreme importance.

The main concern surrounding water quality is the free-

dom of the water from microorganisms that can cause disease.

Typically, these agents are associated with the intestinal tract

of warm-blooded animals including humans. Examples of dis-

ease causing bacteria are those in the genera of Salmonella,

Shigella, and Vibrio. As well certain types of the intestinal

bacterium Escherichia colican cause infections. Escherichia

coli O157:H7 has become prominent in the past decade.

Contaminationof drinking water with O157:H7 can be devas-

tating. An infamous example of this is the contamination of

the municipal water supply of Walkerton, Ontario, Canada in

the summer of 2000. Several thousand people became ill, and

seven people died as a direct result of the O157:H7 infection.

The contamination of the well water in Walkerton

occurred because of run-off from adjacent cattle farms. This

route of water contamination is common. For this reason, the

surveillance of wells for the presence of bacteria is often done

more frequently following a heavy rain, or at times of the year

when precipitation is marked.

The intestinal tract also harbors virusesthat can con-

taminate water and cause disease. Some examples of these

viruses are rotavirus, enteroviruses, and coxsackievirus.

A number of protozoan microorganisms are also prob-

lematic with respect to water quality. The two most prominent

protozoans are in the genera Giardiaand Cryptosporidium.

These microorganisms are resident in the intestinal tract of

animals such as beaver and deer. Their increasing prevalence

in North America is a consequence of the increasing encroach-

ment of civilized areas on natural areas.

Municipal drinking water is usually treated in order to

minimize the risk of the contamination of the water with the

above microbes. Similarly, the protection of water quality by

the boiling of the water has long been known. Even today, so-

called “boil water orders” are issued in municipalities when

the water quality is suspect. The addition of disinfectant com-

pounds, particularly chlorine or derivatives of chlorine, is a

common means utilized to kill bacteria in water. Other treat-

ments that kill bacteria include the use of a gaseous ozone, and

irradiation of water with ultraviolet light to disrupt bacterial

genetic material. In more recent decades, the filtering of water

has been improved so that now filters exist that can exclude

even particles as tiny as viruses from the treated (or “fin-

ished”) water. The killing of the protozoan microorganisms

Collecting water for analysis.

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