Classifying H. pylori

Domain: Eubacteria
Kingdom: Bacteria
Phylum: Proteobacteria
Class: Epsilonproteobacteria
Order: Campylobacterales
Family: Helicobacteraceae
Genus: Helicobacter
Species: Helicobacter pylori

For phylogenic tree, click here

Domain Eubacteria: H. pylori is in this domain because it has  no nuclear membrane, no organelles (except for ribosomes), and its genetic material is found within a single strand of circular chromosome.

Kingdom Bacteria: H. pylori is considered a bacterium because it is a unicellular microorganism that lacks a nucleus.  It also has no membrane bound organelles.

Phylum Proteobacteria: H. pylori falls under this phylum because when a gram stain is performed, it stays pink, indicating that it is a Gram-negative bacterium.  Its outer membrane consists of lipopolysaccharides, rather than peptidoglycan as found in Gram-positive bacteria.  As seen in H. pylori, many of these bacteria use flagella for movement but some are sessile (non-motile), or move via gliding.  This phylum gets its name from the Greek god Proteus, who could change his shape because of the wide variety of bacterial forms found in it.

Class Epsilonproteobacteria: Most of the bacteria within this class inhabit the intestinal tract of mammals.  They can either be symbionts (either benefiting or not affecting the host) or parasites such as H. pylori.

Order Campylobacterales:  This order is composed of mesophiles, meaning they live in moderate temperatures (10-50C).  The human stomach, which is the habitat for H. pylori, falls within this range.

Family Helicobacteraceae: This family is characterized by the helical shape of its members.

Genus Helicobacter: Members of this genus live in the acidic mammalian stomach by producing urease.  They are all flagellated and can move quite fast.  This genus  was once part of the Campylobacter genus but was later made into its own group.

Species Helicobacter pylori: H. pylori is the most widely known species of the Helicobacter genus.  It is pathogenic to humans, and it is the topic of this entire website!

**Classification information from