Biomedical Engineering Reference
In-Depth Information
Epsilon Proteobacteria, like all other proteobacteria, are Gram negative
bacteria, with an inner and outer membrane enclosing the cell wall. These
bacteria are curved or spiral-shaped and most genera live in the digestive
tracts of animals. Two genera are pathogenic in humans: Campylobacter and
Helicobacter. Helicobacter species live in the stomach. Campylobacter species
live in the duodenum.
Epsilon Proteobacteria
Campylobacterales
Helicobacteraceae
*Helicobacter
Campylobacteraceae
*Campylobacter
More than half of the world's human population is infected by Helicobacter
pylori. Infection rates are highest in developing countries. Helicobacter
pylori lives in the stomach, an organ that, for many years, was thought to be
sterile: no bacteria could possibly survive the acidic environment of the gas-
tric lining! In 1983, Robin Warren and Barry Marshall described what they
called “unidentified curved bacilli” in patients with gastritis, by direct visual-
ization under a microscope. These structures were later proved to be
Helicobacter pylori. To demonstrate the viability and the pathogenicity of these
organisms, Marshall experimented on himself, by ingesting gastric juice from a
“dyspeptic” man. About ten days later, he developed gastritis, suggesting that
an agent in stomach contents from patients with gastritis, could transmit the dis-
ease to other people. Marshall and Warren submitted their findings in a scien-
tific abstract, which was rejected by the Australian Gastroenterological
Association [42]. Luckily for us, these two stalwart scientists persevered. In
2005, the Nobel prize for medicine was awarded to Robin Warren and Barry
Marshall for discovering the role of Helicobacter pylori in gastric disease. In
retrospect, we now know that these bacteria were observed in histologic exami-
nation of gastritis specimens as early as 1875 [43]. Until Warren and Marshall,
nobody made the cognitive leap, connecting the visualized organisms to a
human disease; pathologists were intellectually invested in the false belief that
the stomach was a sterile organ.
The mechanism of transmission of Helicobacter has not been conclusively
determined, but the organism has been isolated from feces, saliva, and tooth
plaque from infected individuals, suggesting a direct human-to-human spread
[44]. Infections tend to be persistent. Helicobacter pylori is believed to be a
common cause of peptic ulcers, chronic gastritis, duodenitis, and stomach
cancers; both adenocarcinoma of stomach and MALT (mucosa-associated lym-
phoid tissue) lymphoma. Since the discovery of Helicobacter pylori, a variety
of additional Helicobacter species have been isolated from animals and from
humans; many are enteropathogenic. Examples are Helicobacter suis,
Helicobacter felis, Helicobacter bizzozeronii,andHelicobacter salomonis.
