Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Hygiene

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sers. The material that emerges from hydrothermal vents is

extremely hot (up to 750° F [398.89° C]) and is very rich in

minerals such as sulfur. The minerals can precipitate out of

solution to form chimneys. The construction of a chimney can

occur quickly. Growth of 30 feet in 18 months is not unusual.

The tallest of these chimneys that has been measured was the

height of a 15 story building.

A vibrant community of bacteria, tubeworms that are

unique to this environment, and other creatures exists around

hydrothermal vents. The entire ecosystem is possible because

of the activity of the bacteria. These bacteria have been shown,

principally through the efforts of the Holger Jannasch

(1927–1998) of Woods Hole Oceanographic Institution, to

accomplish the conversion of sulfur to energy in a process that

does not utilize sunlight called chemosynthesis. The energy is

then available for use by the other life forms, which directly

utilize the energy, consume the bacteria, or consume the

organisms that rely directly on the bacteria for nourishment.

For example, the tubeworms have no means with which to

take in or process nutrients. Their existence relies entirely on

the bacteria that live in their tissues.

See alsoChemoautotrophic and chemolithotrophic bacteria;

Extremophiles; Sulfur cycle in microorganisms

HHygieneYGIENE

Hygiene refers to the health practices that minimize the spread

of infectious microorganismsbetween people or between

other living things and people. Inanimate objects and surfaces,

such as contaminated cutlery or a cutting board, may be a sec-

ondary part of this process.

One of the bedrock fundamentals of hygiene is hand-

washing. The recognition of the link between handwashing

and reduction in microbial illness dates back to the mid-nine-

teenth century. Then, Florence Nightingale, based on her nurs-

ing experiences during the Crimean War, wrote about her

perceived relationship between unsanitary conditions and dis-

ease. At about the same time, the Viennese physician Ignaz

Philipp Semmelweisnoted the connection between mortalities

in hospital patients and the movement of physicians from

patient to patient without an intervening washing of their

hands. After Semmelweis introduced hand washing with a

solution containing chloride, the incidence of mortality due to

puerperal fever (infection after childbirth) diminished from

18% to less than 3%. Now, hand washing with similar anti-

septic agents and even with plain soap and water is known to

reduce illness and death from hospital acquired infections.

Proper hygienic practices in the hospital setting not only

save lives, but save a great deal of money also. According to

the Centers for Disease Control, the cost of dealing with the

2.4 million hospital acquired urinary tract infections, blood

stream infections, respiratory infections and infections of inci-

sions, which are caused each year by microbes transferred

from hospital staff to the patient, and which could be pre-

vented by proper hand washing, is over 4 billion dollars in the

United States alone.

Similarly, in the home and other social settings, hand

washing can prevent the spread of infectious microorganisms.

A common route of infection is from the bathroom to the

kitchen. Improper hand washing fails to remove microorgan-

isms, such as Escherichia coliand Salmonellaacquired from

fecal excretion. Handling of food transfers the organisms to

the food.

Hygiene is not so concerned with the bacterial flora that

normally resides on the skin. These bacteria include

Corynebacterium, Proprionibacterium, and Acinetobacter.

These organisms are tenaciously associated with the skin and

so are not as easily removed by the mechanical scrubbing

action of hand washing. Rather, hygienic efforts such as hand

washing attempt to remove organisms, such as Escherichia

colithat become transiently associated with the skin. The tran-

sient organisms tend be removed more easily and are more apt

to be infectious.

In medical environments, hygiene is not only manda-

tory, but must be done according to established procedures.

For example, both before and after seeing a patient, a physi-

cian must wash his/her hands with an alcohol-based prepara-

tion if hands are not visibly dirty, and with soap and water if

dirt is apparent. This practice is also done if any contact with

microorganisms has occurred or is even suspected of occur-

ring (for example, handling a surgical instrument that is not

wrapped in a sterile package) and after removing surgical

gloves. The latter is important since the interior of a surgical

Hand washing is a means of preventing the spread of bacterial and

viral infections.

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