This page offers information about the Lyme disease causing bacterium Borrelia burgdorferi.
In 1981 the causative agent of Lyme disease was discovered by Willy Burgdorfer, who managed to isolate spirochetes (a type of bacteria) belonging to the genus Borrelia out of Ixodes-ticks.
Some other well-known species of Borrelia include Borrelia recurrentis, Borrelia hermsii and Borrelia miyamotoi, which are all associated with Relapsing fever, which is another infectious disease.
Later this spirochete got the name Borrelia burgdorferi, named after its discoverer. Another well-known spirochete is Treponema pallidum, that causes syphilis in humans. Spirochetes are a group of bacteria that have a spiral, corkscrew shape and a unique way of moving through lash-like appendages that are called flagella.
Spirochetes are usually much longer than they are wide, and their width is often too small to be able to see them with an ordinary light microscope. Borrelia burgdorferi can have a length of 20-30 μm, but a width of only 0.2-0.3 μm (μm = micrometer). Therefore, dark field microscopy must be used to see spirochetes. A dark-field microscope has a special condenser that directs light in an angle from the sides instead of straight from the bottom to the object. This way the particles or cells are visible as bright objects against a dark background.
Borrelia burgdorferi has an optimal growth of 32° C, in a micro-aerobic environment (= with low oxygen levels). But even under optimal conditions, the generation time is slow with about 12 to 24 hours. The medium for the lab culture of Borrelia burgdorferi is Barbour-Stoenner-Kelly (BSK).
Borrelia burgdorferi is not classified as a gram positive or gram negative bacterium, although with the Gram stain it is weakly negative and it does have some characteristics of gram negative bacteria, but there are also differences.
The Borreliae that cause Lyme disease are divided into several genospecies (subspecies), of which the three most well-known are:
I. Borrelia burgdorferi (sensu stricto)
II. Borrelia garinii
III. Borrelia afzelii
Sometimes to avoid confusion, the term Borrelia burgdorferi sensu stricto is used to indicate that one is referring to this particular genospecie, while the term that is used to describe all genospecies together is Borrelia burgdorferi sensu lato. However, generally simply the name Borrelia burgdorferi is used.
In the Unites States Borrelia burgdorferi sensu stricto is predominant, while in Europe and Asia all three genospecies exist, although Borrelia garinii and Borrelia afzelii are predominant there. The strains differ in clinical symptoms and presentation.
The life cycle of Borrelia burgdorferi goes together with that of the tick and the hosts of the tick. Mice serve as the principal reservoir for the bacteria and have been shown to remain infected for life. Ixodes ticks transmit Borrelia burgdorferi to other hosts of the tick.
Borrelia burgdorferi penetrates the blood and tissues of various infected mammals and birds. In nature, Borrelia burgdorferi exists in small and larger animals like mice and deer. When a tick has a first blood meal on an infected animal, often a small one like a rodent, the tick can get infected. The tick can transfer the spirochetes over to another animal on their next blood meal, usually a larger animal like a deer, pet and also humans and other warm blooded animals. An infection with Borrelia burgdorferi can cause Lyme disease in humans, dogs, cats, horses, and other animals.
Besides its usual motile spirochete-form, Borrelia burgdorferi may also exist in other forms, although this is subject to debate. Particularly there is evidence that there is a cystic or coccoid form of Borrelia burgdorferi in which the spirochetes are encysted in a protective sheath (like a cocoon), and wherein the cell wall may be missing or altered. Also, there may be dormant (latent) cells of Borrelia burgdorferi that don't reproduce and are hardly active for many months. In such cases successful treatment of Lyme disease with antibiotics may be more difficult.
Further there are studies in which the researchers supposedly saw cell wall deficient forms (CWD-form) of Borrelia burgdorferi, although it might actually have been the cyst-form that they saw and mistaken them for cell wall deficient forms. Research from recent years also suggests that Borrelia burgdorferi creates biofilms that helps it survive from the immune system and antibiotics. However, the existence of a Borrelia biofilm is not generally accepted. Lastly, some people claim that Borrelia burgdorferi can produce neurotoxins, but there isn't solid evidence to support this claim. Borrelia burgdorferi can be killed by various types of antibiotics, including common types like doxycycline and amoxicillin.