Microbiology and Immunology

Chlamydial pneumonia WORLD OF MICROBIOLOGY AND IMMUNOLOGY

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The role of chitin as a support structure is analogous to

the peptidoglycansupportive layer that is a feature of Gram-

positive and Gram-negative bacteria. The think peptidoglycan

layer in Gram-positive bacteria provides a rigid and robust sup-

port. The peptidoglycan layer in Gram-negative bacteria that is

only one molecule thick does not provide the same degree of

structural support. Other mechanical elements of the Gram-

negative cell wall are necessary to shore up the structure.

In the ocean, where many creatures contain chitin, sea-

dwelling bacteria called Vibrio furnisiihave evolved a sensory

system that detects discarded chitin. The bacteria are able to

break down the polymer and use the sugar molecules as meta-

bolic fuel.

See alsoFungi

CChlamydial pneumoniaHLAMYDIAL PNEUMONIA

Chlamydial pneumoniais a pneumonia cause by one of sev-

eral forms of Chlamydial bacteria. The three major forms of

Chlamydiaresponsible for pneumonia are Chlamydia pneu-

moniae, Chlamydia psittaci, and Chlamydia trachomatis.

In reaction to infection, infected lung tissue may

become obstructed with secretions. As part of a generalized

swelling or inflammationof the lungs, the fluid or pus secre-

tions block the normal vascular exchanges that take place in

the alveolar air sacs. Blockage of the alveoli results in a

decreased oxygenation of the blood and deprivation of oxygen

to tissues.

Chlamydia pneumoniae(in older literature known as

“Taiwan acute respiratory agent”) usually produces a condi-

tion known as “walking pneumonia,” a milder form of pneu-

monia that may only result in a fever and persistent cough.

Although the symptoms are usually mild, they can be debili-

tating and dangerous to at risk groups that include the elderly,

young children, or to individuals already weakened by another

illness. Chlamydia pneumoniaespreads easily and the high

transmission rate means that many individuals within a popu-

lation—including at risk individuals can be rapidly exposed.

Species of chlamydiae can be directly detected follow-

ing cultivation in embryonated egg cultures and immunofluo-

rescencestaining or via polymerase chain reaction(PCR).

Chlamydiae can also be detected via specific serologic tests.

Chlamydia psittaciis an avian bacteria that is transmit-

ted by human contact with infected birds, feathers from

infected birds, or droppings from infected birds. The specific

pneumonia (psittacosis) may be severe and last for several

weeks. The pneumonia is generally more dangerous than the

form caused by Chlamydia pneumoniae.

Chlamydia trachomatis is the underlying bacterium

responsible for one of several types of sexually transmitted dis-

eases(STD). Most frequently Chlamydia trachomatisresults

in an inflammation of the urethra (nongonococcal urethritis)

and pelvic inflammatory disease. Active Chlamydia trachoma-

tis infections are especially dangerous during pregnancy

because the newborn may come in contact with the bacteria in

the vaginal canal and aspirate the bacteria into its lung tissue

from coating left on the mouth and nose. Although many new-

borns develop only mild pneumonia, because the lungs of a

newborn are fragile, especially in pre-term babies, any infec-

tion of lung tissue is serious and can be life-threatening.

Specific antibioticsare used to fight chlamydial pneu-

monias. Erythromycin and erythromycin derivatives are used

to combat Chlamydia pneumoniaeand Chlamydia trachoma-

tis. Tetracycline is usually effective against Chlamydia

psittaci.

See alsoBacteria and bacterial infection; Transmission of

pathogens

CHLORAMPHENICOL•seeANTIBIOTICS

CChlorinationHLORINATION

Chlorination refers to a chemical process that is used primarily

to disinfect drinking water and spills of microorganisms. The

active agent in chlorination is the element chlorine, or a deriv-

ative of chlorine (e.g., chlorine dioxide). Chlorination is a

swift and economical means of destroying many, but not all,

microorganisms that are a health-threat in fluid such as drink-

ing water.

Chlorine is widely popular for this application because

of its ability to kill bacteriaand other disease-causing organ-

isms at relatively low concentrations and with little risk to

humans. The killing effect occurs in seconds. Much of the

killing effect in bacteria is due to the binding of chlorine to

reactive groups within the membrane(s) of the bacteria. This

binding destabilizes the membrane, leading to the explosive

death of the bacterium. As well, chlorine inhibits various bio-

chemical reactions in the bacterium. In contrast to the rapid

action of chlorine, other water disinfectionmethods, such as

the use of ozone or ultraviolet light, require minutes of expo-

sure to a microorganism to kill the organism.

In many water treatment facilities, chlorine gas is

pumped directly into water until it reaches a concentration that

is determined to kill microorganisms, while at the same time

not imparting a foul taste or odor to the water. The exact con-

centration depends on the original purity of the water supply.

For example, surface waters contain more organic material that

acts to absorb the added chlorine. Thus, more chlorine needs to

be added to this water than to water emerging from deep under-

ground. For a particular treatment facility, the amount of chlo-

rine that is effective is determined by monitoring the water for

the amount of chlorine remaining in solution and for so-called

indictor microorganisms (e.g., Escherichia coli).

Alternatively, chlorine can be added to water in the form

of a solid compound (e.g., calcium or sodium hypochlorite).

Both of these compounds react with water, releasing free chlo-

rine. Both methods of chlorination are so inexpensive that

nearly every public water purification system in the world has

adopted one or the other as its primary means of destroying

disease-causing organisms.

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