Borrelia burgdorferi bacteria. Coloured scanning electron micrograph (SEM) of Borrelia burgdorferi bacteria, the cause of Lyme disease. These spirochaete (spiral-shaped) Gram-negative bacteria are passed to humans through the bites of infected Ixodes sp. ticks. Symptoms of Lyme disease include skin lesions, muscle pain, neurological and cardiac abnormalities, and arthritis. Treatments include antibiotic and corticosteroid drugs.