Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Antiseptics

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The Chlamydia studies have pointed out the widespread

nature of antigenic mimicry. Other bacteria, viruses, fungiand

protozoashare the antigenic similarity with the mouse anti-

genic region. The bacteria include Borrelia burgdorferi(the

agent of Lyme disease), Treponema pallidum(the causative

agent of syphilis), and Mycoplasma pneumoniae(the cause of

non-viral atypical pneumonia).

Antigenic mimicry may also be the basis of the ulcers

formed upon infection of humans with Helicobacter pylori.

The acidic environment of the stomach would exacerbate host

tissue damage due to an autoimmune response.

Antigenic mimicry supports a hypothesis known as the

“infection hypothesis,” which proposes that common human

diseases are caused by infections. If so, then treatment for

heart disease and stomach ulcers would involve strategies to

eliminate bacterial infections.

See alsoBacteria and bacterial infection; Immunit: active,

passive, and delayed

AAntisepticsNTISEPTICS

Antiseptics are compounds that act to counteract sepsis, which

is an illness caused by a bacterial infectionof the blood.

Antiseptics are able to counteract sepsis by preventing the

growth of pathogenic (disease causing) microorganisms. An

antiseptic may kill a microorganism, but it does not necessar-

ily have to. The treated microbes may only be weakened. The

weaker, slower growing microbes may then be more suscepti-

ble to the defense mechanisms of the host.

The terms antiseptic and disinfectant are used almost

interchangeably nowadays. Yet they do have different mean-

ings. An antiseptic is a chemical or technique that is used on

people. A disinfectant is a chemical that is applied to an inan-

imate object or surface to get rid of microorganisms. An anti-

septic generally does not have the same potency as a

disinfectant. Otherwise, the chemical would harm the tissues

it is in contact with. For this reason, an antiseptic should not

be used to treat inanimate objects. Likewise, the generally

more toxic disinfectant should not be used to treat skin or

areas such as the mucous membranes of the nose.

While more is known of the molecular basis of antisep-

tic actions, the use of antimicrobial compounds is ancient. For

example, the black eye make-up known as kohl, which was

used by the ancient Arabs and Egyptians, is a mixture of cop-

per and antimony. These compounds are antiseptic. Indeed,

the modern cure for trachoma (blindness caused by infection

of the eyes by the bacterium Chlamydia trachomatis) is

remarkably similar in composition to kohl.

There are a number of antiseptics and antiseptic pro-

cedures.

In a health care setting, powerful antiseptics are used to

ensure that the skin is essentially sterile prior to an operation.

Examples of such antiseptics include chlorhexidine and

iodophors (iodine-containing compounds). Alcohol is an anti-

septic, which is routinely used to swab the skin prior to an

injection. Alcohol acts to coagulate the protein in bacteria.

The irreversible change in the protein is lethal to the bacteria.

In the example of the injection, alcohol swabbing of the injec-

tion site will kill the bacteria on the skin, so that living bacte-

ria are not carried into the body upon insertion of the needle.

Dilution of alcohol, so that a solution is 30% alcohol by vol-

ume, makes this antiseptic even more potent, as it allows the

alcohol to permeate into the bacteria. Pure alcohol rapidly

coagulates surface proteins, producing a coagulated crust

around the bacteria.

Another antiseptic is carbolic acid. This is also known

as phenol. The coal tar-based product was discovered in 1834.

Originally phenol was poured down sewers to kill microor-

ganisms. Over time, its use expanded. In 1863, the British sur-

geon Joseph Listerbegan using a spray of phenol to disinfect

open wounds during surgery. Prior to his innovation, such sur-

gery was only performed when all other avenues of treatment

had failed, since the risk of death from infection was

extremely high.

Still another antiseptic compound is pine oil. It is

added to household disinfectants more because of its pleas-

ant smell than its aseptic power nowadays. In fact, it inclu-

sion actually weakens the bacteria-killing power of the

household disinfectant.

Lister’s method was supplanted by the adoption of

extreme cleanliness in the operating room, such as the use of

sterile masks, gloves and gowns, in order to keep the surgical

area free of microorganisms. This approach is known as anti-

septic surgery. As strange as it may seem now, surgeons in

Lister’s era often did not change or clean their operating garb

between operations. A surgeon would often commence an

operation wearing a gown covered with the blood and germs

of many previous operations. Prior to the introduction of anti-

sepsis in the operating room, the rate of death following sur-

gery was almost 60%. After the introduction of antisepsis, the

recorded death rate in England dropped to four per cent.

Hand washing has also become standard practice in the

hospital and the home.

Another antiseptic technique is sterilization. The use of

steam at higher than atmospheric pressure is an effective

means of killing many types of bacteria, including those that

form spores.

In the home, antiseptics are often evident as lotions or

solutions that are applied to a cut or scrape to prevent infec-

tion. For these uses, it is necessary to clean the affected area

of skin first to dislodge any dirt or other material that could

reduce the effectiveness of the antiseptic. Antiseptics, partic-

ularly those used in the home, are designed for a short-term

use to temporarily rid the skin of microbes. The skin, being

in primary contact with the environment, will quickly

become recolonized with microorganisms. Long-term use of

antiseptics encourages the development of populations of

microorganisms that are resistant to the antiseptic.

Additionally, the skin can become irritated by the long expo-

sure to the harsh chemical. Some people can even develop

allergiesto the antiseptic.

Another hazard of antiseptics that has only become

apparent since the 1990s is the contaminationof the environ-

ment. Antiseptic solutions that are disposed of in sinks and toi-

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