MicroBiology-Draft/Sample

Epsilonproteobacteria

The smallest class of Proteobacteria isEpsilonproteobacteria, which are gram-negative microaerophilic bacteria
(meaning they only require small amounts of oxygen in their environment). Two clinically relevant genera of
Epsilonproteobacteria areCampylobacterandHelicobacter, both of which include human pathogens.Campylobacter
can cause food poisoning that manifests as severe enteritis (inflammation in the small intestine). This condition,
caused by the speciesC. jejuni, is rather common in developed countries, usually because of eating contaminated
poultry products. Chickens often harborC. jejuniin their gastrointestinal tract and feces, and their meat can become
contaminated during processing.

Within the genusHelicobacter,the helical, flagellated bacteriumH. pylorihas been identified as a beneficial member
of the stomach microbiota, but it is also the most common cause of chronic gastritis and ulcers of the stomach
and duodenum (Figure 4.12). Studies have also shown thatH. pyloriis linked to stomach cancer.[12]H. pyloriis
somewhat unusual in its ability to survive in the highly acidic environment of the stomach. It produces urease and
other enzymes that modify its environment to make it less acidic.

Figure 4.12 Helicobacter pylorican cause chronic gastritis, which can lead to ulcers and stomach cancer.

Table 4.6summarizes the characteristics of the most clinically relevant genera of Epsilonproteobacteria.

Class Epsilonproteobacteria

Example

Genus

Microscopic

Morphology

Unique Characteristics

Campylobacter Gram-negative,

spiral-shaped

rod

Aerobic (microaerophilic); often infects chickens; may infect humans via

undercooked meat, causing severe enteritis

Helicobacter Gram-negative,

spiral-shaped

rod

Aerobic (microaerophilic) bacterium; can damage the inner lining of the

stomach, causing chronic gastritis, peptic ulcers, and stomach cancer

Table 4.6

1. Name two Epsilonproteobacteria that cause gastrointestinal disorders.


2. S. Suerbaum, P. Michetti. “Helicobacter pyloriinfection.”New England Journal of Medicine347 no. 15 (2002):1175–1186.

156 Chapter 4 | Prokaryotic Diversity

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