Microbiology and Immunology

Psychrophilic bacteria WORLD OF MICROBIOLOGY AND IMMUNOLOGY

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ments. One such alteration is the production of a glycocalyx

around the bacteria. The bacteria become very hard for the

immune systemto eradicate. The immune response eventually

damages the epithelial cells of the lung. So much so, some-

times, that lung function is severely compromised or ceases.

Another bacterium, Pseudomonas cepacia, is also an

opportunistic cause of lung infections in those afflicted with

cystic fibrosis. This species is problematic because it is resist-

ant to more antibioticsthan is Pseudomonas aeruginosa.

Glycocalyx production in some strains of Pseudomonas

aeruginosacan be so prodigious that colonies growing on solid

media appear slimy. Indeed, some species produce such

mucoid colonies that the colonies will drip onto the lid of the

agarplate when the plate is turned upside down. These slimy

growths are described as mucoid colonies, and are often a hall-

mark of a sample that has been recovered from an infection.

Disease-causing species of Pseudomonascan possess a

myriad of factors in addition to the glycocalyx that enable a

bacterium to establish an infection. The appendages known as

pili function in adherence to host cells. A component of the

outer membrane possesses an endotoxin. Finally, a number of

exotoxins and extracellular enzymescan cause damage at a

distance from the bacterium. One such exotoxin, which is

called toxin A, is extremely potent, and may be the prime

cause of damage by the bacteria in infections.

Some species, especially Pseudomonas aeruginosaare

a problem in hospitals. By virtue of their function, hospitals

are a place where many immunocompromised people are

found. This is an ideal environment for an opportunistic dis-

ease-causing bacterium. Moreover, Pseudomonas aeruginosa

has acquired resistance to a number of commonly used antibi-

otics. As yet, a vaccineto the bacterium does not exist.

Prevention of the spread of Pseudomonasinvolves the obser-

vance of proper hygiene, including handwashing.

See alsoBacteria and bacterial infection; Infection and resist-

ance; Lipopolysaccharide and its constituents

PPsychrophilic bacteriaSYCHROPHILIC BACTERIA

Psychrophilic (“cold loving”) microorganisms, particularly

bacteria, have a preferential temperature for growth at less

than 59° Fahrenheit (15° Celsius). Bacteria that can grow at

such cold temperatures, but which prefer a high growth tem-

perature, are known as psychrotrophs.

The discovery of psychrophilic microorganisms and the

increasing understanding of their functioning has increased

the awareness of the diversity of microbial life on Earth. So

far, more than 100 varieties of psychrophilic bacteria have

been isolated from the deep sea. This environment is very cold

and tends not to fluctuate in temperature. Psychrophilic bacte-

ria are abundant in the near-freezing waters of the Arctic and

the Antarctic. Indeed, in Antarctica, bacteria have been iso-

lated from permanently ice-covered lakes. Other environ-

ments where psychrophilic bacteria have been include high

altitude cloud droplets.

Psychrophilic bacteria are truly adapted for life at cold

temperatures. The enzymesof the bacteria are structurally

unstable and fail to operate properly even at room (or ambient)

temperature. Furthermore, the membranes of psychrophilic

bacteria contain much more of a certain kind of lipid than is

found in other types of bacteria. The lipid tends to be more pli-

able at lower temperature, much like margarine is more pliable

than butter at refrigeration temperatures. The increased fluid-

ity of the membrane makes possible the chemical reactions

that would otherwise stop if the membrane were semi-frozen.

Some psychrophiles, particularly those from the Antarctic,

have been found to contain polyunsaturated fatty acids, which

generally do not occur in prokaryotes. At room temperature,

the membrane of such bacteria would be so fluid that the bac-

terium would die.

Aside from their ecological curiosity, psychrophilic

bacteria have practical value. Harnessing the enzymes of these

organisms allows functions such as the cleaning of clothes in

cold water to be performed. Furthermore, in the Arctic and

Antarctic ecosystems, the bacteria form an important part of

the food chain that supports the lives of more complex crea-

tures. In addition, some species of psychrophiles, including

Listeria monocytogenesare capable of growth at refrigeration

temperatures. Thus, spoilage of contaminated food can occur,

which can lead to disease if the food is eaten. Listeriosis, a

form of meningitisthat occurs in humans, is a serious health

threat, especially to those whose immune systemis either not

mature or is defective due to disease or therapeutic efforts.

Other examples of such disease-causing bacteria include

Aeromonas hydrophila, Clostridium botulinum, and Yersinia

enterocolitica.

See alsoExtremophiles

PPublic health, current issuesUBLIC HEALTH, CURRENT ISSUES

Public health is the establishment and maintenance of healthful

living conditions for the general population. This goal requires

organized effort from all levels of government. Underlying the

current concerns in public health are three principle aims of

public health efforts. First is the assessment and monitoring of

populations, from the community level to the national level, to

identify populations who are at risk for whatever health prob-

lem is being considered. For example, public health efforts

have shown that aboriginals in Canada are especially prone to

developing diabetes. The second “plank” of public health is the

formulation of policies to deal with the significant problems.

Returning to the example, policies and strategies for action are

now being formulated to reverse the trend. The third core pub-

lic health function is to assure that everyone is able to receive

adequate and affordable care and disease prevention services.

There are many microbiological threats to public health.

In order to maintain the three cores of public health, priorities

must be established. In organizations such as the Centers for

Disease Controland the World Health Organization, different

divisions have been created to address the different concerns.

Within each division the particular area of concern, such as

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