Which of the following best describes spirochete cells?

Which of the following statements is true about spirochete cells?

Which of the following diseases is commonly associated with spirochete bacteria?

What is a distinguishing feature of spirochete bacteria?

*Treponema* is a genus of spirochetes that contains several human pathogens, including the species *Treponema pallidum*, which is further divided into multiple subspecies causing syphilis and tropical diseases of the skin, bones, and joints.

*Treponema*

*Borrelia burgdorferi* is a pathogenic spirochete species that causes Lyme disease. It is transmitted to humans by tick vectors from the genera *Ixodes* and *Amblyomma*, and infection often produces a 'bull's eye' rash, fever, fatigue, and sometimes debilitating arthritis.

*Borrelia burgdorferi*

*Borrelia recurrens* is a pathogenic spirochete species that causes relapsing fever, a condition marked by recurring cycles of fever.

*Borrelia recurrens*

The axial filament is a specialized, flagellum-like structure that wraps around a spirochete cell. Unlike typical external flagella, it runs internally inside the cell body, residing in the periplasmic space between the outer membrane and the plasma membrane. The rotation of this internal filament is what enables the high motility of spirochetes.

Axial Filament

*Treponema pallidum* is a species of spirochete that is classified into four subspecies: *T. pallidum pallidum*, which causes the sexually transmitted infection syphilis, and three other subspecies (*T. pallidum pertenue*, *T. pallidum carateum*, and *T. pallidum endemicum*) that cause tropical infectious diseases affecting the skin, bones, and joints.

*Treponema pallidum*

Spirochetes are gram-negative bacteria characterized by long, spiral-shaped bodies that can reach lengths up to $${}250$$ μm. Due to their extreme thinness, they are difficult to view under conventional brightfield microscopes, typically requiring darkfield fluorescent microscopy instead, and are highly difficult or impossible to culture in a laboratory.

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Individual cells of a specific prokaryotic organism typically exhibit a characteristic shape, known as cell morphology. While thousands of prokaryotic organisms exist, only a handful of morphologies are commonly seen microscopically. These standard shapes include spherical (coccus), rod-shaped (bacillus), curved comma-shaped (vibrio), short oval-like rods (coccobacillus), long rigid corkscrews (spirillum), and loose, flexible helical spirals (spirochete).

Cell Morphologies

Non-proteobacteria gram-negative bacteria are a group of gram-negative bacteria that do not belong to the Proteobacteria phylum. This group includes spirochetes, the Cytophaga-Flavobacterium-Bacteroides (CFB) group, Planctomycetes, and Chlamydia species.

Non-proteobacteria Gram Negative Bacteria

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Microbiology covers the scope and sequence requirements for a single-semester microbiology course for non-majors. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of the text make the material interesting and accessible while maintaining the career-application focus and scientific rigor inherent in the subject matter. Microbiology’s art program enhances students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs.

Microbiology is produced through a collaborative publishing agreement between OpenStax and the American Society for Microbiology Press. The book aligns with the curriculum guidelines of the American Society for Microbiology.

OpenStax Microbiology Textbook

The genus *Mycoplasma* consists of more than $${}100$$ species of bacteria that lack a cell wall and are classified as low G+C gram-positive bacteria, despite not staining with Gram-stain reagents. These bacteria are extremely small, with some diameters around $${}0.2$$ μm, which is smaller than certain large viruses. Due to the absence of a cell wall, *Mycoplasma* cells are pleomorphic, meaning they lack a fixed shape, can assume diverse forms, and may resemble tiny animal cells, making them challenging to identify.

Mycoplasmas

Pathogenic bacteria are bacteria that can cause infectious disease.

Pathogenic Bacteria

Which of the following bacterial morphologies is characterized by a spiral shape?

Which bacterial morphology is described as rod-shaped?

Which bacterial morphology is described as spherical in shape?

Which bacterial morphology is described as comma-shaped?

The term coccus (plural: cocci) is used to describe prokaryotic cells that possess a round, spherical shape.

Coccus

The term vibrio (plural: vibrios) is used to describe prokaryotic cells that are shaped like curved rods, closely resembling a long comma.

Vibrio

The term coccobacillus (plural: coccobacilli) refers to prokaryotic cells that appear as short rods, closely resembling ovals.

Coccobacillus

The term spirillum (plural: spirilla) describes prokaryotic cells that possess a long, spiral shape, visually resembling a corkscrew.

Spirillum

Spirochete

Pleomorphism is the biological characteristic of certain cells or microorganisms, such as *Mycoplasma* species, that allows them to assume a variety of shapes rather than having a single characteristic morphology.

Pleomorphism

The term bacillus (plural: bacilli) refers to rod-shaped prokaryotic cells. In taxonomy, Bacillus is also a genus of low G+C gram-positive bacteria, many of which can form resilient endospores.

Bacillus

Planctomycetes is a phylum of aquatic bacteria inhabiting freshwater, saltwater, and brackish environments. They reproduce by budding rather than binary fission, producing a motile swarmer cell from a maternal cell. This swarmer cell eventually attaches to a surface using an appendage called a holdfast and differentiates into an immobile (sessile) cell, which is the only stage capable of reproduction.

Planctomycetes

Gram-negative cells possess a cell envelope with a significantly thinner layer of peptidoglycan—no more than about $${}4$$ nm thick—compared to gram-positive cells. Their overall cell envelope structure is highly complex, featuring a periplasmic space and an outer membrane located external to the peptidoglycan layer.

Gram Negative Cell Walls

The *Chlamydia* genus consists of many pathogens. They spread very easily from host to host because they form elementary bodies during their life cycle. These are spore-like which allows *Chlamydia* to be metabolically inactive until they are in a host environment.

*Chlamydia*

The *Cytophaga-Flavobacterium-Bacteroides* (CFB) group is a phylum of phylogenetically diverse, rod-shaped, gram-negative nonproteobacteria. These bacteria are anaerobic organoheterotrophs and avid fermenters that share similarities in their DNA nucleotide sequences and are adapted to anaerobic environments, such as the human mouth or gut, where they can be mutualistic or pathogenic.

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