Microbiology, 2021

4.3 • Nonproteobacteria Gram-Negative Bacteria and Phototrophic Bacteria 149
Within the genus Helicobacter, the helical, flagellated bacterium H. pylori has 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 4.11). Studies have also shown that H. pylori is linked to stomach cancer. 12 H.
pylori is 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 4.11
Helicobacter pylori can cause chronic gastritis, which can lead to ulcers and stomach cancer.
Table 4.6 summarizes 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
CHECK YOUR UNDERSTANDING
• Name two Epsilonproteobacteria that cause gastrointestinal disorders.
4.3 Nonproteobacteria Gram-Negative Bacteria and
Phototrophic Bacteria
Learning Objectives
By the end of this section, you will be able to:
• Describe the unique features of nonproteobacteria gram-negative bacteria
• Give an example of a nonproteobacteria bacterium in each category
• Describe the unique features of phototrophic bacteria
• Identify phototrophic bacteria
12 S. Suerbaum, P. Michetti. “Helicobacter pylori infection.” New England Journal of Medicine 347 no. 15 (2002):1175–1186.