Spirochete – Definition, Morphology, Diseases

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What is Spirochete?

  • Spirochetes, scientifically denoted as Spirochaetota, belong to a unique phylum of bacteria characterized by their distinct diderm (double-membrane) gram-negative cellular structure. One of the most distinguishing features of these bacteria is their elongated, helically coiled morphology, reminiscent of a corkscrew. This spiral configuration is the very reason behind their nomenclature, with “spiro” meaning spiral and “chaete” referring to hair.
  • These microorganisms exhibit chemoheterotrophic behavior, deriving their energy from chemical sources and organic compounds. They vary in size, with lengths ranging from 3 to 500 μm and diameters spanning from approximately 0.09 to 3 μm.
  • A salient feature that sets spirochetes apart from other bacterial groups is the presence of endoflagella, sometimes referred to as axial filaments. These structures are anchored at both poles of the bacterium, situated within the periplasmic space, which lies between the inner and outer cellular membranes. The endoflagella extend along the length of the cell, and their rotation induces a unique twisting motion, enabling the spirochete to navigate its environment. This mode of movement is particularly advantageous, allowing spirochetes to traverse viscous mediums such as mucus, blood, and even certain host tissues.
  • Reproduction in spirochetes occurs through asexual transverse binary fission. While many of these bacteria are free-living and anaerobic, there are notable exceptions. The phylum is diverse, not only in terms of its pathogenic potential but also in its ecological habitats and molecular attributes, including variations in guanine-cytosine content and overall genome size.
  • Spirochetes have been identified in a plethora of environments, from aquatic habitats to the stomachs of various animals. While some form symbiotic relationships, others are known pathogens, causing diseases like Lyme disease and syphilis. Interestingly, certain spirochetes have been detected in marine bivalves, where they maintain a neutral, commensal relationship.
  • In conclusion, spirochetes are a multifaceted group of bacteria, distinguished by their spiral morphology and unique mode of motility. Their ability to move efficiently through dense mediums, coupled with their diverse habitats and pathogenic potential, makes them a significant subject of study in the realm of microbiology.
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Definition of Spirochete

Spirochete is a type of bacteria characterized by its elongated, helically coiled (corkscrew-shaped) morphology, belonging to the phylum Spirochaetota. These bacteria are known for their unique movement mechanism using endoflagella and can be found in diverse environments, with some species causing diseases like Lyme disease and syphilis.

Taxonomic organization of the spirochetes

The taxonomic organization of spirochetes is rooted in the comprehensive frameworks provided by the List of Prokaryotic names with Standing in Nomenclature (LPSN) and the National Center for Biotechnology Information (NCBI). The following delineates the hierarchical structure of this bacterial phylum:

Phylum: Spirochaetota

  • Class: Spirochaetia
    • Order: Leptospirales
      • Family: Leptospiraceae
        • Genera: Leptonema, Leptospira, Turneriella
    • Order: Brachyspirales
      • Family: Brachyspiraceae
        • Genera: Brachyspira, “Ca. Maribrachyspira”
    • Order: Brevinematales
      • Families: Brevinemataceae, “Longinemaceae”, “Thermospiraceae”
        • Genera: Brevinema, “Longinema”, ?Thermospira
    • Order: “Exilispirales”
      • Family: “Exilispiraceae”
    • Order: Spirochaetales
      • Families: “Pillotinaceae”, Borreliaceae, Sphaerochaetaceae, Spirochaetaceae
        • Genera: ?Pillotina, Borrelia, Borreliella, “Ca. Ornithospirochaeta”, Marispirochaeta, Sediminispirochaeta, Sphaerochaeta, Alkalispirochaeta, Salinispira, Spirochaeta
    • Order: “Treponematales”
      • Families: Breznakiellaceae, “Rectinemataceae”, Treponemataceae
        • Genera: Breznakiella, Gracilinema, Leadbettera, Rectinema, Treponema

This classification underscores the diversity within the Spirochaetota phylum, with each genus and species having distinct biological and ecological roles. The systematic arrangement provides a clear understanding of the relationships and evolutionary lineage of these bacteria, facilitating scientific research and medical interventions.

Pathogenic Mechanism of Spirochetes

Spirochetes are a unique group of bacteria, some of which are responsible for causing significant diseases in humans and animals. Their pathogenicity is attributed to a combination of their structural features, ability to evade the host immune response, and the toxins they produce. Here’s a detailed look at the pathogenic mechanisms employed by spirochetes:

  1. Unique Morphology: The helical shape of spirochetes and their endoflagella allow them to move in a corkscrew manner, enabling them to penetrate host tissues, including mucous membranes and tight junctions, effectively.
  2. Immune Evasion:
    • Antigenic Variation: Some spirochetes, like those causing relapsing fever, can change their surface proteins, allowing them to escape detection by the host’s immune system.
    • Physical Seclusion: Spirochetes can hide within cells or in privileged sites (like the central nervous system) where the immune response is limited.
    • Biofilm Formation: Some spirochetes can form biofilms, which are protective communities of bacteria that can resist immune responses and antibiotic treatments.
  3. Toxins and Enzymes: Spirochetes produce various enzymes and toxins that can damage host tissues. For instance, the hyaluronidase enzyme helps in breaking down connective tissues, facilitating the spread of the bacteria.
  4. Adhesion to Host Cells: Spirochetes have specific surface proteins that allow them to adhere to host cells, an essential step in establishing infection.
  5. Invasion of Host Cells: Some spirochetes can invade host cells, which not only provides them with a protective environment but also allows them to access nutrients.
  6. Dissemination: After initial colonization, spirochetes can spread to various organs and tissues, leading to systemic infections. Their motility plays a crucial role in this dissemination.
  7. Inflammatory Response: The presence of spirochetes can trigger a strong inflammatory response in the host. While this is a defense mechanism, the inflammation can cause tissue damage, contributing to the symptoms of the disease.
  8. Persistence in Host: Some spirochetes, like the one causing Lyme disease, can persist in the host for a long time, leading to chronic symptoms.

Diseases caused by spirochetes, such as syphilis (by Treponema pallidum), Lyme disease (by Borrelia burgdorferi), and leptospirosis (by Leptospira species), showcase the effectiveness of these pathogenic mechanisms. Understanding these mechanisms is crucial for developing effective treatments and preventive measures against spirochetal diseases.

Morphology and Characteristics of Spirochete

Spirochetes are a unique group of bacteria, distinguishable by their specific morphological and functional attributes. Here, we delve into the primary characteristics that define this bacterial group:

  1. Endoflagella (Axial Flagella): One of the hallmark features of spirochetes is the presence of endoflagella, sometimes referred to as axial flagella. These structures originate from the periplasmic space at each pole of the bacterium and extend backward, spanning the entire length of the cell.
  2. Cell Shape and Movement: The endoflagella not only contribute to the helical or corkscrew shape of the spirochetes but also facilitate their distinct modes of movement. These bacteria can exhibit a range of motions, including flexion, extension, rotation along their longitudinal axis, and translational movement, all attributed to the dynamic nature of their flagella.
  3. Reproductive Mechanism: Spirochetes reproduce asexually through a process known as transverse binary fission. This method involves the bacterium dividing transversely to produce two daughter cells.
  4. Habitat: Spirochetes predominantly inhabit liquid environments. They can be found in a variety of mediums, including blood, lymph, water, and mud, showcasing their adaptability to diverse ecological niches.
  5. Oxygen Requirements: While the majority of spirochetes are anaerobic, thriving in environments devoid of oxygen, there are exceptions. Some species have evolved to live in oxygen-rich environments, highlighting the diverse metabolic capabilities within this bacterial group.
  6. Pathogenic Potential: Spirochetes are not just benign inhabitants of their environments. Several species within this group have evolved to become pathogens, causing a range of diseases in humans.

In summary, spirochetes, with their distinctive morphology and diverse characteristics, play varied roles in nature, from benign environmental inhabitants to potent human pathogens. Their unique features, especially the presence of endoflagella, set them apart in the vast world of bacteria.

Spirochetes as Parasites

Spirochetes, a unique group of bacteria recognized for their helically coiled structure, have garnered significant attention in the medical community due to their role as causative agents of various diseases. Three primary genera within the spirochetes are known to harbor pathogenic species:

  1. Treponema: The species Treponema pallidum is notorious for causing syphilis, a sexually transmitted disease. Other species within this genus are responsible for diseases like yaws, pinta, and bejel, which manifest as skin and mouth sores, bone lumps, and skin discolorations. These conditions can be transmitted through sexual contact or direct skin-to-skin contact. Fortunately, a simple penicillin injection can effectively eliminate these bacteria.
  2. Leptospira: This genus encompasses species that lead to Leptospirosis, sometimes referred to as Weil’s disease. Initial symptoms resemble the flu, presenting as fever, headaches, and muscle aches. However, if untreated, the condition can escalate to severe complications like meningitis and pulmonary hemorrhage.
  3. Borrelia: Comprising 52 species, this genus is primarily transmitted through tick and lice bites. Out of these, 21 species are implicated in Lyme disease, while the remaining 29 are associated with Relapsing Fever, characterized by recurring episodes of fever, chills, headaches, nausea, and rashes.

Lyme Disease: A Closer Look

  • Lyme disease, caused by certain species of Borrelia, is a prevalent condition transmitted through tick bites. The disease manifests initially as an expanding rash, followed by a range of symptoms, from severe headaches and neck stiffness to arthritis and neurological complications. In extreme cases, Lyme disease can be lethal.
  • The insidious nature of Lyme disease lies in its delayed onset of symptoms and the spirochete’s sophisticated mechanisms to evade the host’s immune system. Upon entering the host, the Borrelia spirochete employs a protein from the tick’s saliva to cloak itself, rendering it invisible to the immune system. This stealth mode allows the bacterium to establish its presence and spread throughout the body, leveraging the motility provided by its endoflagella.
  • Furthermore, the spirochete can modify its outer cell wall proteins, effectively altering its appearance and confounding the immune system. This constant change hinders the immune system’s ability to produce effective antibodies, leading to a toxic response that causes inflammation and tissue damage.
  • Additionally, spirochetes have the capability to embed themselves within the host’s extracellular matrix, further evading immune detection. They can also infiltrate lymph nodes, disrupting the normal antibody production process.
  • A particularly concerning defense mechanism employed by Borrelia is the formation of biofilms. These self-generated protective barriers house the bacteria and other microorganisms, shielding them from antibiotics and allowing them to remain dormant until conditions become favorable for resurgence.

In summary, spirochetes, with their advanced evasion techniques and pathogenic potential, underscore the importance of early detection and treatment in combating the diseases they cause.

Spirochetes as Symbionts

While spirochetes are often associated with pathogenicity, a significant number of these bacteria engage in symbiotic interactions, where both the host and the spirochete benefit from the relationship.

1. Symbiosis in Termites:

The termite species Mastotermes darwiniensis harbors a flagellate known as “Mixotricha” within its digestive system. Remarkably, the surface of Mixotricha is densely populated with Treponema spirochetes, giving it a ciliated appearance. These spirochetes, through coordinated undulatory movements, propel Mixotricha within the termite’s intestinal fluid, while Mixotricha’s anterior flagella facilitate steering.

The primary role of Mixotricha is to assist in the degradation of cellulose from the wood consumed by the termite, converting it into sugars, hydrogen, carbon dioxide, and acetate. It is postulated that the associated spirochetes participate in the oxidation of acetate, catering to the termite’s respiratory needs. In return, the spirochetes benefit from the nutrients generated by Mixotricha’s metabolic activities.

2. Symbiosis in Ruminants:

Ruminants, including animals like cows, sheep, and deer, possess a specialized four-chambered stomach designed to digest cellulose-rich plant matter. The initial chamber, known as the ‘rumen,’ is a microbial haven, teeming with fungi, bacteria, and protozoans. These microorganisms produce enzymes essential for cellulose breakdown, enzymes that ruminants inherently lack.

Within the rumen’s microbial consortium, Treponema spirochetes are present, albeit in smaller proportions. These spirochetes, akin to their counterparts in termites, facilitate the cellulose degradation process. They utilize the metabolic by-products of other rumen microorganisms for their sustenance and growth.

The subsequent chambers of the ruminant stomach, namely the ‘reticulum,’ ‘obassum,’ and ‘abomasum,’ are involved in other digestive processes, including liquid absorption and the digestion of food through gastric acids.

In conclusion, spirochetes, beyond their pathogenic roles, play pivotal parts in symbiotic relationships, showcasing the intricate balance and interdependence that exists in nature. Their presence in diverse ecosystems, from termite intestines to ruminant stomachs, underscores their adaptability and the multifaceted roles they play in the broader biological tapestry.

Disease Causing Organisms

Spirochetes, a unique group of bacteria, encompass several genera responsible for various diseases in humans. Here, we explore the disease-causing organisms within the Spirochete phylum:

  1. Genus Treponema:
    • Treponema spirochetes are characterized by their slender structure, fine spirals, and either rounded or pointed termini.
    • T. pallidum is the causative agent of venereal syphilis, a sexually transmitted infection that progresses through primary, secondary, and tertiary stages. The primary stage is marked by painful genital ulcers, followed by skin rashes and mucosal lesions in the secondary stage. The tertiary stage can lead to severe complications, including aneurysms and granulomata.
    • Other species, such as T. endemicum, T. pertenue, and T. carateum, are responsible for endemic syphilis, yaws, and pinta, respectively.
  2. Genus Borrelia:
    • Borrelia spirochetes are large, motile bacteria with wide and irregular coils.
    • B. recurrentis induces relapsing fever, characterized by recurring episodes of fever. The disease can be louse-borne or tick-borne, with the latter caused by species like B. hermsii, B. duttoni, and B. parkeri.
    • B. burgdorferi is the pathogen behind Lyme disease, which manifests initially as skin lesions, followed by systemic symptoms like fever and joint pain. The tertiary stage can lead to chronic conditions, including arthritis and encephalopathy.
    • B. vincenti causes Vincent’s angina, a gum infection resulting in symptoms like bleeding, ulcers, and fever.
  3. Genus Leptospira:
    • Leptospira are thin spirochetes with numerous coiled spirals and distinctive hooked ends.
    • Leptospira interrogans is responsible for leptospirosis, a zoonotic disease transmitted to humans through water contaminated by the urine of carrier animals. Symptoms range from mild fever and rashes to severe complications, including jaundice and abdominal pain.

In conclusion, while spirochetes exhibit a wide range of ecological roles, certain species are pathogenic, causing significant diseases in humans. Recognizing and understanding these organisms is crucial for effective diagnosis and treatment.


Which of the following is a distinguishing feature of spirochetes?
a) Gram-positive cell wall
b) Presence of endoflagella
c) Obligate aerobes
d) Non-motile nature

Which disease is caused by Treponema pallidum?
a) Lyme disease
b) Leptospirosis
c) Syphilis
d) Relapsing fever

Borrelia burgdorferi is responsible for which condition?
a) Yaws
b) Lyme disease
c) Pinta
d) Vincent’s angina

Spirochetes are primarily found in which type of environments?
a) Dry and arid
b) Liquid environments like blood and lymph
c) Acidic environments
d) Alkaline environments

Which spirochete is known to cause relapsing fever?
a) Treponema pertenue
b) Borrelia recurrentis
c) Leptospira interrogans
d) Borrelia burgdorferi

The primary mode of reproduction in spirochetes is:
a) Budding
b) Sporulation
c) Transverse binary fission
d) Longitudinal binary fission

Which spirochete is associated with a symbiotic relationship in the termite gut?
a) Borrelia
b) Leptospira
c) Treponema
d) Brachyspira

Which disease is characterized by a bull’s-eye rash and is caused by a spirochete?
a) Yaws
b) Syphilis
c) Lyme disease
d) Pinta

Which of the following spirochetes is known to cause a zoonotic disease called leptospirosis?
a) Borrelia burgdorferi
b) Treponema pallidum
c) Leptospira interrogans
d) Brachyspira hyodysenteriae

The unique corkscrew movement of spirochetes is attributed to:
a) Pili
b) Capsule
c) Endoflagella
d) Fimbriae


What are Spirochetes?

Spirochetes are a group of spiral-shaped bacteria that are characterized by their unique corkscrew movement and the presence of endoflagella.

How are Spirochetes different from other bacteria?

Spirochetes are distinguished by their spiral shape and the presence of endoflagella, which are located between the outer and inner membranes and give them their characteristic movement.

What diseases are caused by Spirochetes?

Spirochetes are responsible for several diseases in humans, including syphilis (caused by Treponema pallidum), Lyme disease (caused by Borrelia burgdorferi), and relapsing fever (caused by various Borrelia species).

How are Spirochete infections transmitted?

Transmission varies depending on the species. For instance, syphilis is sexually transmitted, Lyme disease is transmitted through tick bites, and leptospirosis is transmitted through contact with contaminated water or soil.

Are all Spirochetes pathogenic?

No, not all spirochetes are pathogenic. While some cause diseases in humans and animals, others live in symbiotic relationships with their hosts or exist freely in the environment.

How are Spirochete infections diagnosed?

Diagnosis is typically based on clinical symptoms, history of exposure, and laboratory tests such as microscopy, serological tests, and molecular techniques like PCR.

How are Spirochete infections treated?

Spirochete infections are primarily treated with antibiotics. The choice of antibiotic and duration of treatment depend on the specific infection and its severity.

Can Spirochete infections be prevented?

Prevention strategies depend on the specific disease. For instance, Lyme disease can be prevented by avoiding tick bites, while syphilis can be prevented by practicing safe sex.

What is the significance of Spirochetes in the environment?

Spirochetes play a role in various environmental processes. For example, some spirochetes are involved in the degradation of organic matter, while others live in symbiotic relationships with insects, aiding in digestion.

Are there any vaccines available against Spirochete infections?

As of now, there are no commercially available vaccines against most spirochete infections, including syphilis and Lyme disease. However, research is ongoing to develop effective vaccines.


  1. Cole, J. R. (1990). Spirochetes. Diagnostic Procedure in Veterinary Bacteriology and Mycology, 41–60. doi:10.1016/b978-0-12-161775-2.50009-8
  2. Haake, D. A. (2009). Spirochetes. Encyclopedia of Microbiology, 278–292. doi:10.1016/b978-012373944-5.00230-3
  3. https://step1.medbullets.com/microbiology/121562/introduction-to-spirochetes
  4. https://ucmp.berkeley.edu/bacteria/spirochetes.html

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