Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Globulins

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in the world. In North America, giardiasis is the leading cause

of non-bacterial diarrhea. The diarrhea typically persists for a

few weeks to a few months, although in extreme cases the

infection can persist for years. Infection produces a general

malaise and considerable weight loss. The diarrhea tends to be

mushy but, in contrast to the diarrhea produced in bacterial

and amoebic dysentery, it is not bloody. Other symptoms of

giardiasis include flatulence, sore abdomen, foul-smelling

breath and, particularly in infants, the disruption of normal

body growth. Research on animal models has also demon-

strated that the infection disrupts the ability of the intestinal

epithelial cells to absorb nutrients from the intestinal contents.

The decreased absorption of compounds such as vitamin B 12

and lactose can have deleterious effects on overall health.

The molecular basis of the infection is still not fully

resolved. However, the trophozoite form of the protozoan is

required, as is associated with the surface of the intestinal

epithelial cells. In contrast to another intestinal disease caus-

ing microbe, Entamoeba histolytica, Giardia lambliadoes not

invade the host tissue. Studies with animal models have indi-

cated that the symptoms of giardiasis may be due to a physi-

cal barrier to the absorption of nutrients, the disruption of

intestinal structures called microvilli by the adherent protozoa,

and production of a toxin that damages the epithelial cells.

During an active infection, trophozoites undergo divi-

sion to new daughter trophozoites. Also, formation of cysts

occurs and the cysts are excreted with the feces in huge num-

bers. These can be passed onto someone else to establish a

new infection.

Treatment for giardiasis can include the use of antibi-

otics. Often, however, the malady is self-limiting without

intervention. Prevention of giardiasis is a more realistic

option, and involves proper treatment of drinking water and

good hygienic practices, especially handwashing.

Currently, the detection of Giardiais based on the

microscopic detection of either form of the protozoan,

although animal models of the infection are being researched.

The infection has been produced in gerbils. The lack of a rou-

tine detection method is problematic for water treatment. The

need for rapid testing of drinking water for Giardiais pressing

as the incidence of infection is increasing, with the encroach-

ment of human habitation on previously pristine areas.

See alsoAmebic dysentery; Parasites; Water quality

GGliding bacteriaLIDING BACTERIA

Gliding bacteriais a term that refers to any bacteria that

exhibit a gliding or creeping type of movement (also known as

motility) when in contact with a solid surface.

There are hundred of types of gliding bacteria. Most are

beneficial or benign to humans and animals. Some strains,

such as the myxobacteria, produce antibioticsand compounds

that act on tumors. In addition, some strains of gliding bacte-

ria can degrade compounds, and so have potential in the

biodegradation of pollutants. However, some strains are a

major health concern. For example, gliding bacteria that live

in human saliva can cause gum disease, and can be life-threat-

ening if they enter the bloodstream. Other types of gliding

bacteria cause disease in animals and fish.

The gliding motility of myxobacteria is only one of sev-

eral forms the organism can adopt. Another form consists of a

stalk with fruiting bodies positioned at one end. When exhibit-

ing gliding motility, a single cell can be in motion or a popu-

lation of cells can move in concert with one another. The latter

type of gliding seems to require the group of cells. If a cell

moves out in front of the others, the lead cell will soon stop.

The nature of the communal movement is unknown.

The gliding motility of bacteria such as those in the

myxobacteria, the green nonsulfur group of bacteria (such as

Chloroflexus auranticus) and the nonphotosynthetic gliding

bacteria (such as Herpetosiphon) has long been a fascination

to bacteriologists. The bacteria glide smoothly with no evi-

dence of cellular involvement in the movement. In fact, the

gliding motion may be the result of what have been termed

“slime fibrils,” a complex of proteins, which are attached to

the bacterium at one end and to the solid surface at the other

end. The exact mechanism of action of the slime fibrils is still

unresolved. If the fibrils have to move to propel a bacterium

along, the nature of this movement and how the movement is

powered remain unknown.

Some gliding bacteria are known to exhibit a chemotac-

tic response, that is, a concerted movement either in the direc-

tion of an attractant or concerted movement away from a

repellent. The chemical sensing system must be coordinated

with the gliding mechanism. Again, the nature of this coordi-

nation is unresolved.

See alsoBacterial movement

GGlobulinsLOBULINS

Globulins are immune molecules that are produced by the

immune systemin response to invasion of the body of agents

that are perceived by the system as being foreign. Some

immune globulins are also known as antibodies. Examples of

microorganismsthat stimulate globulin production are bacte-

ria, viruses, molds, and parasites.

The production of globulins is triggered by the presence

of the foreign material (antigen). Through an intricately coor-

dinated series of events, the immune system responds to the

presence of an antigen by the production of a corresponding

globulin. There are three divisions of globulins, based on the

movement of the molecules through a gel under the influence

of an electric current (in other words, based on their size and

their charge character). The three types are alpha, beta, and

gamma globulins.

Alpha globulins are manufactured mainly in the liver.

There are a number of so-called alpha-1 and alpha-2 globulins.

The functions of these globulins includes the inhibition of an

enzyme that digests protein, an inhibitor of two compounds

vital in the clumping (coagulation) of blood, and a protein that

can transport the element copper.

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