The bacterium Borrelia burgdorferi is recognized as the primary cause of Lyme disease, a tick-borne illness that can affect multiple body systems. Its distinctive shape is fundamental to its survival and ability to cause disease. This unique form allows it to navigate diverse environments within both its tick vector and human host, influencing how the infection establishes and progresses. Understanding this shape provides insight into its adaptability and pathogenic mechanisms.
Describing the Spirochete Form
Borrelia burgdorferi is classified as a spirochete, characterized by its slender, helical, or corkscrew-like appearance. Unlike many other bacteria that are spherical (cocci) or rod-shaped (bacilli), Borrelia burgdorferi maintains a flexible, undulating body. Its dimensions are 0.2 to 0.3 micrometers wide and 5 to 20 micrometers in length, giving it a long, thin profile.
This distinctive morphology is maintained by a flexible cell wall and an outer membrane that encloses its internal structures. The overall shape can be described as a flat wave or a loose spiral, allowing for significant flexibility. This flexibility differentiates it from more rigid bacterial structures and enables its characteristic movement.
Movement Enabled by Shape
The spirochete shape of Borrelia burgdorferi directly facilitates its unique motility. This bacterium possesses internal flagella, called periplasmic flagella, located within the periplasmic space between its inner and outer membranes. These flagella are not external appendages like those found on many other bacteria; instead, they wrap around the protoplasmic cell cylinder in a ribbon-like configuration.
The rotation of these periplasmic flagella causes the entire cell body to twist and undulate. This rotation, driven by large flagellar motors at each end of the bacterium, generates a powerful torque that propels the spirochete forward in a corkscrew or drilling motion. This unique propulsion allows Borrelia burgdorferi to efficiently navigate through highly viscous host tissues, which would impede most other bacteria.
Shape’s Role in Disease Progression
The spirochete shape and its corkscrew motility enable Borrelia burgdorferi to cause and spread Lyme disease throughout the host. After transmission from an infected tick, the bacterium’s drilling motion allows it to penetrate and disseminate through dense host tissues, including the skin, connective tissues, and later, the nervous system and joints. This invasive capability enables the bacterium to move from the initial bite site into the bloodstream, where it can circulate to infect various organs.
The flexible, undulating shape also contributes to the bacterium’s ability to evade the host’s immune responses. By moving through dense tissues and potentially entering host cells, Borrelia burgdorferi can avoid direct exposure to immune cells and antibodies. Its ability to penetrate and spread systemically allows it to establish persistent infections, leading to the varied and often long-lasting symptoms associated with Lyme disease.