Selenomonads

Taxonomy and Classification

Bacteria known as selenomonads have the following taxonomic position in microbiological classification:

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

This taxonomy determines their phylogenetic relationships with other anaerobic microorganisms and accounts for commonalities in certain physiological processes.

Ecological niche

Representatives of the genus Selenomonas are widespread both within the host organism and in the external environment. Their main habitats include:

1. Mammalian and human body:
2. Gastrointestinal tract (GIT).
3. Oral mucosa.
4. Genital tract.
5. Human skin.
6. Environment:
7. Contaminated water bodies (where suitable anaerobic conditions for their survival are established).

Morphological and tintorial properties

Upon microscopic examination, selenomonads demonstrate marked polymorphism.

• Shape: Bacteria appear as polymorphic rods that can be curved or spiral. A characteristic feature is the presence of tapered ends.
• Gram staining: Gram-negative (G-), indicating a cell wall structure with a thin peptidoglycan layer and an outer membrane.
• Motility: Microorganisms are actively motile. Their flagellation type is classified as lophotrichous, meaning that a whole tuft of flagella is located at one of the poles or on the lateral surface of the bacterial cell, providing directed movement.

Cultural and biochemical characteristics

Isolation and maintenance of selenomonad growth in laboratory conditions require strict adherence to cultivation rules:

• Oxygen relation: Obligate anaerobes. Any contact with molecular oxygen is detrimental to their metabolism.
• Nutrient media requirements: Microorganisms require complex, multicomponent nutrient media. Specific growth factors must be added to the medium for successful growth.
• Biochemical activity: Exhibit pronounced saccharolytic activity. In particular, they are capable of fermenting lactose, resulting in the formation of end products in the form of acid and gas.
• Antigenic structure: The bacterial cell wall contains somatic O-antigen.

Resistance and stability

Selenomonads have extremely low resistance to environmental factors, especially oxygen:

• Air relation: As with fusobacteria, exposure to open air results in instant cell death.
• Chemical agent relation: Bacteria are fully sensitive to the action of common antiseptics and standard disinfectants used in medical practice.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

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

Other topics in the section "Gram-positive spore-forming bacilli (Anthrax, Clostridia: tetanus, botulism, gas gangrene, difficile)"

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