An Introduction To Spirochetes

The toxicity and invasiveness of bacterial infections are frequently used to classify them. The ability of a bacteria to infect a huge variety of tissue in its host determines its invasiveness. 

Spirochetes, a genus of bacteria that causes diseases like syphilis, Lyme disease, relapse fever, and leptospirosis, are among the most invasive mammalian pathogens. 

An Introduction To Spirochetes

The majority of spirochetes are distinguished by their different forms and movements.

They are lengthy, thin bacteria with morphologies that range from flat waves to helices to more irregular morphologies.

Spirochetes, along with many other bacteria, move by using long, helical appendages called flagella; however, spirochetes contain a flagella inside the periplasm, which is the thin gap in between outer and inner membranes. 

The flagella inside the periplasm rotate and/or undulate, causing the cell body to revolve and/or undulate.

The power that controls the movement of these organisms is produced by these bacterial deformations, and it is this peculiar motility that permits the bacteria to be very invasive in mammals. 

This review will summarise the present level of knowledge on these organisms’ characteristics, motility and biomechanics, as well as evidence for how this knowledge might help us better comprehend spirochetal illnesses.

Functions Of Bacteria 

Bacteria encompass all groups of microscopic single-celled organisms found in vast numbers in practically every location on Earth, ranging from deep-sea vents to deep beneath the surface of the Earth to human digestive tracts.

Bacteria, which lack the membrane-bound nucleus as well as other internal components, are classified as prokaryotes, or unicellular living forms. 

Prokaryotes are the most common living organisms on Earth, having existed for roughly three-quarters of the planet’s history and adapted to practically every available biological niche.

Bacteria have a wide range of metabolic capabilities as a group, and can feed on practically any organic substance as well as some inorganic compounds. 

Although certain bacteria can inflict disease in humans, animals, and plants, the vast majority are harmless environmental agents whose metabolism support higher life forms.

Other bacteria live as symbionts with plant life and invertebrates, where they perform crucial services for the host such as nitrogen fixation as well as cellulose breakdown. 

Soil would not be fruitful without prokaryotes, and dead organic matter would decompose much more slowly. 

Bacteria are commonly employed in the manufacturing of meals, chemicals, and medications.

The study of the interactions between diverse species of bacteria continues to give fresh insights about the origins of life on Earth and evolutionary mechanisms.

Structural Diversity In Bacteria 

Despite the fact that bacterial cells are significantly smaller and have a simpler structure from eukaryotic cells, bacteria are a diverse group of creatures that vary in size, shape, environment, and metabolism. 

Many of our current understandings of bacteria originate from research of illness causing bacteria, which are easier to isolate in bacterial culture and analyse than many free-living bacterium species. 

It’s worth noting as many free-living bacteria aren’t the same as bacteria that have evolved to live as parasites or symbionts on animals.

As a result, there seem to be no absolute principles for bacterial composition and structure, and any general statement is subject to numerous exceptions.

What Are Spirochetes?

Spirochetes are responsible for a wide range of animal diseases, including the well-known human ailments Lyme disease and Syphilis.

Yaws, relapsing fever, leptospirosis and periodontal disease are all caused by spirochetes in humans.

Spirochetes are bacteria with a spiral form. Some are harmless members of the natural mucosal flora, whereas others are dangerous diseases.

Borrelia, Leptospira, Treponema, and Spirillum are the four genera that cause disease in humans. 

The treponema pallidum variant pallidum causes syphilis (previously known as lues). In most situations, it is a persistent systemic disease that is transmitted sexually.

Borrelias are divided into two groups: those that cause Lyme disease or those that cause relapsing fever. 

Borrelia burgdorferi and related borrelias are the pathogens that cause Lyme disease in Europe. Hard ticks are the carriers of the disease.

They can be free-living or attached to a host. They can live in the oral cavity, humans’ gastrointestinal tracts, mammals’ gastrointestinal tracts, insects’ gastrointestinal tracts, and marine settings. 

The treponemes, Borrelia burgdorferi, and Leptospira interrogans are the most common spirochetal infections in humans. 

Rifampin, which is commonly employed in microbiological isolation, is resistant to all of them.

Treponema is anaerobic, whereas Borrelia is microaerophilic and Leptospires is aerobic.

The Structure Of Spirochetes

The form of spirochetes is one of their most distinguishing features. Spirochetes are usually long and thin, with helical or flat-waveforms. 

They, like all bacteria, have a cell membrane that divides the inside from the outside of the cell. 

Spirochetes have a spiral form due to a flexible peptidoglycan cell wall that is looped around numerous axial fibrils.

An outer bilayered membrane completely covers the cellular structure and axial fibrils, comparable to the outer layer of other gram-negative bacterium.

A hyaluronic acid sludge coating accumulates around the outside of some species, which may contribute to their pathogenicity.

Spirochetes can rotate and flex, and this motility is thought to be caused by mobility of the axial filament.

The cytoplasm is a packed liquid environment that houses the genome as well as a variety of proteins, and the bacterial cell wall is a narrow, mesh-like coat of peptidoglycan which provides structural stability and serves to define cell shape just beyond the inner membrane. 

The protoplasmic cylinder is a composite structure made up of a cell wall, inner membrane, and cytoplasm.

Finally, this cell cylinder is surrounded by an outer membrane.

The periplasm is a small gap in between cellular membranes that is roughly 20–40 nm thick. 

The periplasm, in addition to housing the cell wall, also comprises long, narrow helically-shaped structures that are physically and chemically similar to flagella from several other bacteria. 

Each of the bacterium’s periplasmic flagella has its own flagellar motor, which is lodged inside the interior membrane and attached to a cell wall near each end. 

As a result, periplasmic flagella connect near the bacterium’s ends and coil inwards along the cell body.

Spirochetes can also have a large number of flagella attached near each end, ranging from 1 to 100.

The periplasmic flagella appear essential in driving the movement of these organisms, just as they are in many bacteria (and will be explored later).

The flagella, on the other hand, perform a skeletal function in many spirochetes. 

Facts About Spirochetes

1. Skin or mucous membranes are commonly used as entrance points.

2. They spread widely and quickly via blood, tissue, and body fluids, affecting cardiovascular, neurologic, and cutaneous tissues in particular.

3. Their outer membrane is devoid of surface proteins. This aids them in evading the immune system.

4. Spirochetes that are neurotropic penetrate the nervous system early in the disease.

5. B. burgdoferi and T. pallidum seem to be latent until they activate in the CNS. This makes counselling more difficult. Because leptospires and recurring fever organisms do not appear to be dormant in the CNS, their treatment is simpler.

6. Spirochetal illnesses progress in stages, with latent periods in between.

7. Infection in untreated hosts can extend anywhere from weeks or months.

Spirochetes And Microscopy

Routine microscopy makes it difficult to see many spirochetes. Despite being gram negative, many of them do not accept stains well and are too thin (0.15 m or less) to fit inside the light microscope resolving capability. 

These spirochetes can only be seen with a darkfield microscope, immunofluorescence, and specific staining procedures.

Borrelia and other spirochetes are larger and more noticeable in stained preparations, including normal blood smears.

Classification And Growth Of Spirochetes

Classification And Growth Of Spirochetes

In vitro, parasite spirochetes develop more slowly than most other bacteria that cause disease.

Some species, such as the syphilis causative agent, have never been cultivated in cell culture for more than a few generations. 

Some are severe anaerobes, while others require low oxygen concentrations and are aerobic.

Spirochete taxonomy is immature in comparison to other bacterial groups.

Spirochetes have a wide range of phenotypic manifestations due to significant variances in their genotypes.

In fact, the deoxyribonucleic acid base makeup of spirochetes varies widely, with guanine plus cytosine levels varying from 36 to 66 mol percent.

Spirochetes have been divided into five genera based on physiological distinctions, as well as ecology, morphology, and other factors.

Cristispira, Spirochaeta, Treponema, Leptospira, and Borrelia are some of the bacteria that cause infections.

Spirochetes Metabolism 

Spirochete metabolism has been studied in a limited amount of research.

This lack of effort could be attributed to the fact that spirochetes were an ill-defined category of microbes for several years following their discovery, garnering the attention of just a limited percentage of microbial physiologists. 

Furthermore, many spirochetes, particularly those associated with anaerobic hosts, are difficult to bulk culture due to their dietary requirements. 

Such cultivable anaerobic host-linked spirochetes are typically produced on complex mediums with blood serum, serum constituents, ascitic fluids, or rumen fluid. 

For a few host-associated anaerobic spirochetes, chemically specified growth media have been identified, some of which have over 50 medium components.

Borrelia burgdorferi

Borrelia burgdorferi is a spirochete bacteria with a helical structure. It possesses a flexible cell wall, as well as an outer and inner membrane. 

The protoplasm is found inside the cell membranes of bacteria and is long and cylinder shaped due to the spiral form of the bacteria. The cell is usually only 1 metre broad, but it might be 10 to 25 metres long.

Borrelia burgdorferi seems to be a tick-borne obligatory parasite with a wide range of small mammals as its natural reservoir.

Infection among these natural hosts does not cause disease, but infection of humans can cause Lyme disease based on the human immunopathological reaction to B. burgdorferi. 

Bacterial compounds that enable B. burgdorferi to multiply and thrive, rather than real virulence factors, appear to be the primary requirement for the bacteria to cause infection in a susceptible host, which is consistent with the aetiology of Lyme disease.

Dr. Alan Steere along with his associates first defined Lyme disease as an infectious sickness in 1977, and it is now the most common vector-borne illness in the U.S.

Because of the geographic grouping of patients within rural areas as well as the seasonal incidence of symptoms, 

Steere hypothesised that Lyme disease was transmitted by an insect vector.

Spirochetes were later discovered inside the midgut tissues of ticks gathered in a Lyme disease infected area by Dr. Willy Burgdorfer. 

When these spirochetes were put into rabbits, they caused a skin rash that looked like erythema migrans, while sera from Lyme disease patients responded with the germs in indirect immunofluorescence assays.

B. burgdorferi sensu strictu, B. garinii, and B. afzelii, which are together called B. burgdorferi sensu lato in Europe and Asia, are the three varieties of Borrelia accounting for the bulk of human instances of illness. 

The particular species called B. burgdorferi s.s. causes Lyme disease within the United States.

Lyme disease in Europe and North America has certain similarities in terms of clinical signs, including a rash as well as an influenza-like sickness.

Diagnosis For Lyme Disease

Diagnosis For Lyme Disease

Antibodies to the microorganisms can be found in lab tests, which can assist establishing or ruling out the diagnosis. They are as follows:

ELISA – This stands for enzyme-linked immunosorbent assay. ELISA is the most common test for Lyme disease detection. It identifies antibodies for B. burgdorferi.

However, it is seldom utilised as the main basis for diagnosis since it can sometimes produce false-positive results.

Although this test may not be positive in the early stages of Lyme disease, the rash is unusual enough to make a diagnosis with no further testing in persons who reside in Lyme disease-infested areas.

Western blot analysis – This test is frequently performed to verify the diagnosis if the ELISA results are positive.

The Western blot identifies antibodies to various B. burgdorferi proteins in this two-step procedure.

Leptospira interrogans 

Leptospira is a Gram-negative spirochete possessing internal flagella and a body that is flexible and spiral-shaped.

Many serovars of Leptospira interrogans exist depending on the cell surface antigens.

The bacterium species Leptospira interrogans comprises over 200 harmful serovars.

The infectious organisms that induce Leptospirosis are these pathogenic bacteria, also known as Leptospires. 

Both animals and humans are known to be affected by this sickness. Clinical sickness can continue anywhere between a few days to a month or longer, and is usually divided into two phases (febrile and immune). 

The flu-like symptoms of the febrile stage include fever, chills, muscle aches, and a severe headache. 

The first phase usually lasts four to nine days, and the patient is asymptomatic for a short time before the second phase, which includes meningitis, liver problems, jaundice, and renal failure, begins.

The illness is frequently misdiagnosed as encephalitis, meningitis, or influenza due to the wide variety of symptoms. 

The severity of the infection is determined by both the infecting serovar and the host.

In one host, the same serovar can produce mild disease whereas in another, it can cause severe disease. 

Case fatality is modest, but it rises with age, reaching 20% or higher in patients with jaundice and kidney problems.

Leptospirosis is a disease spread by infected animals’ urine. It can be found all over the world, however it is most frequent in temperate and tropical areas.

Cows, pigs, horses, canines, rats, and wild animals have all been detected with Leptospira germs. 

Humans become infected after coming into touch with urine from infected animals in water, food, or soil. 

This can occur as a result of contaminated food and water, coming into contact with contaminated skin (particularly if it is abraded), or coming into contact with mucosal sites like the eyes or nose.

Exposure to polluted water is the most common source of outbreaks.

Diagnosis For Leptospirosis

Serological techniques, such as Microscopic Agglutination Testing (MAT), which identifies serovar-specific antibodies, a solid-phase assay to detect Immunoglobulin M (IgM) antibodies in the body, are the most popular ways to diagnose leptospirosis. 

Leptospira remains in the blood until 4-7 days after the generation of Leptospira-specific antibodies, which are mostly of the IgM class at first. 

Because the MAT has a great sensitivity and enables the identification of group specific antibodies, it is the cornerstone of leptospirosis diagnosis.

The Treponemes

Treponemes are 6 to 15 m long and 0.1 to 0.2 m wide helically coiled corkscrew-shaped cells.

They have a protoplasmic cylinder, a peptidoglycan-cytoplasmic membrane structure, and an outer membrane that surrounds the periplasmic flagella. Binary transverse fission is used for multiplication.

Treponemes cause a variety of clinical symptoms. There is an initial genitalia tract lesion (primary stage) in people with acquired genital syphilis, accompanied by scattered lesions (second stage) and, in around one-third of untreated persons, cardiovascular and neurologic issues (tertiary stage). 

Congenital syphilis infection during pregnancy can cause foetal mortality or birth abnormalities. 

The nonvenereal treponematoses yaws, pinta, as well as endemic syphilis commonly manifest as cutaneous or mucous membrane lesions. T issue and bone abnormalities also can arise from yaws and syphilis.

Treponemes are extremely invasive pathogens that can spread quickly after being inoculated.

The treponemal outer membrane’s unusual structure appears to have a role in evading host immune responses, at least in part. 

Treponemes lack the usual lipopolysaccharide (endotoxin), but they do have a lot of lipoproteins, which cause inflammation.

There are still no recognized nonhuman reservoirs for treponemal infection; humans are the sole known source.

Venereal syphilis is found all over the world and has become a major public health issue in many developing countries in recent decades. 

The highest rates of infectivity relate to highly sexually active age groups.

The frequency of novel syphilis cases declined steadily with the advent of penicillin as a cornerstone of syphilotherapy until 1958, when the pattern reverted and a steady rise began. 

In the late 1980s, there was a significant increase in the number of instances of early syphilis, which was mostly due to crack cocaine use among inner-city minorities.

Improved surveillance systems have helped to manage this syphilis epidemic. Yaws are still common in the tropics, despite significant eradication operations.

Diagnosis For Syphilis 

Because syphilis has numerous clinical symptoms, laboratory testing is a critical part of the diagnosing process.

Treponema pallidum, the etiological agent, cannot be cultivated, and there is no one best alternative test. 

Serology is the most used method for diagnosing syphilis in the laboratory.

Syphilis manifests itself in a variety of ways, and it has many clinical characteristics with several other treponemal as well as nontreponemal disorders. 

As a result, the clinical diagnosis must always be backed up by proper laboratory tests, and the test results must be interpreted in light of the patient’s medical history and physical examination findings.

Although T.pallidum cannot be cultivated in cultures, there are numerous tests for syphilis diagnosis, both direct and indirect. 

The detection of T. pallidum by microscopic inspection of fluid or swabs from lesions, histological study of tissues, and nucleic acid amplification techniques like polymerase chain reaction are all direct diagnostic procedures (PCR).

Serological assays for the identification of antibodies are used in indirect diagnosis.

Summary

Spirochetes are a distinctive bacterial community that can be found in a variety of settings, including soil, deep sea sediments, arthropods, and mammals. 

These microorganisms are responsible for a variety of human diseases, notably syphilis, Leptospirosis, and Lyme disease. 

Spirochetes have a characteristic flat-wave morphology and a spiral form.

This article has provided an overview of the characteristics and functions of spirochetes and the basis of which they cause disease in humans.

Jennifer Dawkins

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