Microbiology and Immunology

Helicobacteriosis WORLD OF MICROBIOLOGY AND IMMUNOLOGY

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HHelicobacteriosisELICOBACTERIOSIS

Helicobacteriosis is an infection of the gastrointestinal tract

that is caused by the Gram-negative, spiral-shaped bacterium

called Helicobacter pylori. Ulcers on the lining of the stomach

and upper intestinal tract characterize the malady. The ulcera-

tion may be a prelude to the development of cancer of the

stomach.

Helicobacteriosis is established following the coloniza-

tion of the stomach by Helicobacter pylori. How the bacteria

are transmitted to a person is still unclear. The prevalence of the

infection in overcrowded environments, especially where chil-

dren are present, indicate that person-to-person transmission is

most likely, and that personal hygieneplays a role in transmis-

sion. Following transmission, the bacterium is able to persist in

the extremely acidic environment of the stomach by burrowing

under the mucous overlay of the stomach epithelial cells, and

because the bacteria produce an enzyme called urease. The

enzyme is able to degrade the gastric acid in the stomach.

Helicobacteriosis invariably becomes chronic. Then, the

infection can also be referred to as chronic gastritis. The infec-

tion can become chronic because initially the infection pro-

duces little or no symptoms. Thus, the immune systemis not

alerted to response to the infection, which provides an oppor-

tunity for the bacterial population to become more tenaciously

established.

In about 15% of those who become infected, ulcers

develop in the stomach or in a region of the upper intestine

called the duodenum. The resulting burning feeling caused by

increased secretion of acid is relieved by over-the-counter

antacids, which can further dissuade people from seeking a

physician’s care for the malady. If the infection is diagnosed

and the bacteria eliminated by antibiotic therapy, the elevated

production of acid stops. But, in the absence of treatment, the

painful ulcers will recur. Why only fifteen per cent of those

who have infections develop ulcers while the other 85% of

infected individuals do not is not clear.

Moreover, the molecular basis for the establishment of

the ulcers is also still not clear. There has been some indica-

tion of toxin involvement. Helicobacter pyloriproduces a

toxin called VacA and a protein called CagA.

More ominously, epidemiologic evidence strongly indi-

cates that Helicobacter pyloristomach infections are associ-

ated with the development of various types of stomach cancers.

For examples, the bacterial infection is nine times more com-

mon in those patients who are diagnosed with cancer of the

stomach, and seven times more common in those people who

have a tumor of the lymphatic tissue. Studies have demon-

strated that even in these advanced cases, the elimination of

Helicobacter pylorican produce a shrinking of the tumors.

Helicobacteriosis can be detected in three ways. The first

way is by obtaining a sample of stomach tissue. Culturing of the

stomach contents on growth media that selects for the growth of

Helicobacter pyloriover other bacteria is used to isolate the

organism. If the region of the stomach where tissue is obtained

is free from bacteria, then an infection can be missed.

A second way of detecting the presence of the bacteria

is by a breath test. Breathing on a specially prepared support

can detect the presence of the urease enzyme that is produced

by Helicobacter pylori. Since this enzyme is not commonly

produced, the detection of the enzyme is a strong indication of

the presence of living bacteria. However, in the absence of the

actual isolation of the bacteria, the breath test cannot be

absolutely diagnostic.

Finally, antibodies produced in response to a

Helicobacter pyloriinfection can be detected by a blood test.

Once detected, the bacterial infection does respond to

antibiotic therapy. Elimination of the infection relieves the

symptoms of helicobacteriosis in 80% of those people who are

infected.

The discovery that helicobacteriosis has a bacterial ori-

gin and the relief of the symptoms upon bacterial eradication

has reinforced the validity of a theory that proposes that many

chronic and autoimmune diseases, such as certain types of

heart disease and rheumatoid arthritis, are caused by an infec-

tion by bacteria or other microbe.

See alsoBacteria and bacterial infection; Microbial flora of

the stomach and gastrointestinal tract

HEMAGGLUTININ(HA) AND

NEURAMINIDASEHemagglutinin (HA) and neuraminidase (NA) (NA)

Hemagglutinin (designated as HA) and neuraminidase (desig-

nated as NA) are glycoproteins. Hemagglutinin and neu-

raminidase protrude from the outer surface of the influenza

virus and neuraminidase is a constituent of the enveloping

membrane that surrounds the viral contents. A glycoprotein is

a protein that contains a short chain of sugar as part of its

structure. The hemagglutinin and neuraminidase glycoproteins

are important in the ability of the virus to cause influenza.

A typical influenza virus particle contains some 500

molecules of hemagglutinin and 100 molecules of neu-

raminidase. These are studded over the surface of the virus.

The illness caused by the influenza virus can be devas-

tating. For example, in 1918 a new genetic variant of the virus

swept around the world and in just over a year over 20 mil-

lion people succumbed to the influenza. The variation was

due to alterations in both the hemagglutinin and neu-

raminidase components of the virus. Further antigenic varia-

tions of these molecules produced a virus that, at least for

some time, was not recognized by the immune system. The

result was localized outbreaks or worldwide outbreaks in

1957, 1962, 1964, 1976, and 1978.

Hemagglutinin derives its name from its activity. The

glycoprotein confers upon the virus the ability to agglutinate,

or clump together, red blood cells. The aggregation compro-

mises the function of the red blood cells. The hemagglutinin

glycoprotein also functions in the binding of the virus to cells,

via the recognition of a chemical structure on the cells surface

called sialic acid. The binding of hemagglutinin to sialic acid

compounds on the surface of cells is the initial event in the

association of the virus with human epithelial cells. These two

activities associated with hemagglutinin are important activi-

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