Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Contamination, bacterial and viral

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Prevention of genetic contamination, via the exchange

of genetic material between the bioengineered microbe and

the natural microbial population, is difficult to prevent.

However, available evidence supports the view that the

genetic traits bred into the bioengineered organism to permit

its detection, such as antibiotic resistance, are not traits that

will be maintained in the natural population. This is because of

the energy cost to the microorganism to express the trait and

because of the mathematical dynamics of population genetics

(i.e., the altered genes are not present in numbers to become

established within the greater population) and the absence of

the need for the trait (the antibiotic of interest is not present in

the natural environment). Hence, contamination prevention

procedures have tended to focus on those aspects of contami-

nation that are both relevant and likely to occur.

As an example of the measures currently in place, the

United States has three agencies that are concerned with the

regulation of biotechnology. These are the Department of

Agriculture, Environmental Protection Agency, and the Food

and Drug Administration. Each of these agencies oversee reg-

ulatory legislation that addresses the contamination of various

natural and commercially relevant environments.

See alsoAsilomar conferences; Biotechnology; Hazard

Analysis and Critical Point Program (HACPP); Laboratory

techniques in microbiology

CContamination, bacterial and viralONTAMINATION, BACTERIAL AND VIRAL

Contamination by bacteriaand virusescan occur on several

levels. In the setting of the laboratory, the growth media, tis-

sues and other preparations used for experimentation can sup-

port the growth of unintended and unwanted microorganisms.

Their presence can adversely influence the results of the

experiments. Outside the laboratory, bacteria and viruses can

contaminate drinking water supplies, foodstuffs, and products,

causing illness. Infection is another form of contamination.

Equipment and growth media used in the laboratory

must often be treated to render them free of microorganisms.

Bacteria and viruses can be present in the air, as aerosolized

droplets, and can be present on animate surfaces, such as the

skin and the mucous membranes of the nasal passage, and on

inanimate surfaces, such as the workbenches in the laboratory.

Without precautions and the observance of what is known as

sterile technique, these microbes can contaminate laboratory

growth media, solutions and equipment. This contamination

can be inconvenient, necessitating the termination of an exper-

iment. However, if the contamination escapes the notice of the

researcher, then the results obtained will be unknowingly

marred. Whole avenues of research could be compromised.

Contamination of drinking water by bacteria and viruses

has been a concern since antiquity. Inadequate sanitation prac-

tices can introduce fecal material into the water. Enteroviruses

and fecal bacteria such as Shigellaand Escherichia coli

O157:H7 are capable of causing debilitating, even life-threat-

ening, diseases. Even in developed countries, contamination

of drinking water remains a problem. If a treatment system is

not functioning properly, water sources, especially surface

sources, are vulnerable to contamination. An example

occurred in the summer of 2000 in Walkerton, Ontario,

Canada. Contamination of one of the town’s wells by

Escherichia coliO157:H7 run-off from a cattle operation

killed seven people, and sickened over two thousand.

Other products can be contaminated as well. An exam-

ple is blood and blood products. Those who donate blood

might be infected, and the infectious agents can be transmitted

to the recipient of the blood or blood product. In the 1970s and

1980s, the Canadian blood supply was contaminated with the

viral agents of hepatitisand acquired immunodeficiencysyn-

drome. At that time, tests for these agents were not as sophis-

ticated and as definitive as they are now. The viruses that

escaped detection sickened thousands of people. Blood sup-

plies in Canada and elsewhere are now safeguarded from con-

tamination by stringent monitoring programs.

Food products are also prone to contamination. The con-

tamination can originate in the breeding environment. For

example, poultry that are grown in crowded conditions are

reservoirs of bacterial contamination, particularly with

Campylobacter jejuni. Over half of all poultry entering pro-

cessing plants are contaminated with this bacterium. Other

food products can become contaminated during processing, via

bacteria that are growing on machinery or in processing solu-

tions. Quality control measures, which monitor critical phases

of the process from raw material to finished product, are help-

ful in pinpointing and eliminating sources of contamination.

Firefighters remove barrel conaining suspected infectious agent.

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