What specific growth factors must be added to nutrient media for culturing Selenomonas?

Cultivation of Selenomonas requires complex media supplemented with specific growth factors.

Which family does the genus Selenomonas belong to?

The genus Selenomonas belongs to the family Acidaminococcaceae, with Selenomonas sputigena as the type species.

What type of flagellation is characteristic of Selenomonas?

They feature lophotrichous flagellation, characterized by a tuft of flagella on the cell surface.

Will Selenomonas survive when cultured in aerobic conditions?

No, they are obligate anaerobes. Much like fusobacteria, they die instantly upon exposure to air.

How do these bacteria ferment lactose?

They ferment lactose with robust production of acid and gas.

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Selenomonas

For medical students2 min readUpdated 2026-10-10

Selenomonas species are gram-negative, obligate anaerobic bacteria characterized by polymorphic, curved, or spiral-shaped rod morphology. They are part of the normal microbiota of mucous membranes and the gastrointestinal tract in mammals, and are also found in environmental sources.

MorphologyGram-negative, curved or spiral rods

MotilityLophotrichous (possess a tuft of flagella)

RespirationObligate anaerobes

EcologyGastrointestinal tract, mucous membranes, skin, contaminated water bodies

Taxonomy and Classification

Bacteria of the genus Selenomonas occupy the following systematic position in microbiological classification:

Family: Acidaminococcaceae.
Genus: Selenomonas.
Type species: Selenomonas sputigena.

This taxonomy defines their phylogenetic relationships with other anaerobic microorganisms and underlies shared physiological processes.

Ecological Niche

Members of the genus Selenomonas are widely distributed in host organisms and the environment. Their primary habitats include:

Mammalian and human hosts:
Gastrointestinal tract (GIT).
Oral cavity mucous membranes.
Genital tract.
Human skin.
Environment:
Contaminated water bodies (providing suitable anaerobic conditions for survival).

Morphological and Staining Properties

Microscopic examination reveals marked polymorphism in Selenomonas species.

Shape: The bacteria appear as polymorphic rods that can be curved or spiral-shaped, characteristically featuring tapered ends.
Gram Stain: Gram-negative, reflecting a cell wall structure with a thin peptidoglycan layer and an outer membrane.
Motility: Actively motile microorganisms. Their flagellation is classified as lophotrichous, meaning a tuft of flagella is located at one of the poles or along the lateral surface of the bacterial cell, driving directed movement.

Cultural and Biochemical Features

Isolation and maintenance of Selenomonas in laboratory settings require strict cultivation protocols:

Oxygen Requirements: Obligate anaerobes. Any exposure to molecular oxygen is lethal to their metabolism.
Nutritional Requirements: The microorganisms require complex, multicomponent growth media. Specific growth factors must be added for successful proliferation.
Biochemical Activity: They exhibit pronounced saccharolytic activity, notably fermenting lactose to produce acid and gas end products.
Antigenic Structure: The bacterial cell wall contains somatic O-antigen.

Resistance and Susceptibility

Selenomonas species exhibit extremely low resistance to environmental factors, particularly oxygen:

Air Tolerance: Similar to fusobacteria, exposure to ambient air results in rapid cell death.
Chemical Agents: The bacteria are fully susceptible to standard antiseptics and common disinfectants used in medical practice.

Mnemonic

Selenomonas — Spiral/curved rods, Supplemented media, Slain by air. Flagellation — Lophotrichous (picture a tuft of lunar rays, since selene means moon).

Frequently asked questions

What specific growth factors must be added to nutrient media for culturing Selenomonas?: Cultivation of Selenomonas requires complex media supplemented with specific growth factors.
Which family does the genus Selenomonas belong to?: The genus Selenomonas belongs to the family Acidaminococcaceae, with Selenomonas sputigena as the type species.
What type of flagellation is characteristic of Selenomonas?: They feature lophotrichous flagellation, characterized by a tuft of flagella on the cell surface.
Will Selenomonas survive when cultured in aerobic conditions?: No, they are obligate anaerobes. Much like fusobacteria, they die instantly upon exposure to air.
How do these bacteria ferment lactose?: They ferment lactose with robust production of acid and gas.

Go deeper

Structure and properties of the somatic O-antigen in Selenomonas
Specific growth factors required for cultivation
Detailed mechanism of lactose fermentation
Comparison of oxygen resistance between Selenomonas and Fusobacterium
Role of Selenomonas sputigena in the oral microbiome