Spirochetes (Gram-Negative)

Treponema pallidum

Spirochetes are tiny gram-negative bacteria that resemble corkscrews. This is a unique group because spirochetes have an additional phospholipid-rich membrane, and periplasmic flagella, which protrude sideways from the cell wall under the outer membrane. Spirochetes are divided into Treponema, Borrelia and Leptospira.

Treponemes do not produce toxins or tissue destructive enzymes. Instead, disease is caused by autoimmune responses.

Treponema pallidum
Causes the STD syphilis. Transmitted by contact with open skin or vaginal, anal or oral sex.

• Stages of syphilis:
1. Painless ulcer and painless regional swelling of lymph nodes. 
2. Rash on palms and soles. Condyloma latum, painless bumps on genitals. Almost any organ can be infected, resulting in fever, weight loss and lymphadenopathy (abnormal lymph node size). 
3. Most patients recover from the symptoms of the secondary stage, but 25% will relapse and develop the symptoms again. 
4. Slow inflammatory damage to organs, blood vessels and nerve cells. Patients either exhibit: Gummas (lesions of the skin and bone); Cardiovascular syphilis (aneurism of the aorta as the media layer becomes necrotic); Neurosyphilis (subacute syphilis, meningovascular syphilis where blood vessels of the brain is infected, tabes dorsalis damaging the spinal cord, general paresis leading to mental deterioration, or asymptomatic).  
• Congenital syphilis:
• Early congenital - symptoms resemble adult secondary syphilis. 
• Late congenital - similar to adult tertiary syphilis except heart damage is rare. 
• Subspecies:
• Endemicum causes skin lesions that are mostly oral. Gummas of the skin and bone may develop. 
• Pertenue causes the disease yaws. Papules and lesions appear on the skin, and later tertiary gummas develop in the skin and bones. 
• Carateum causes the disease pinta. Papules develop, followed by lesions on the skin that turn blue in the sun. 

Borrelia burgdorferi 
Causes lyme disease, transmitted by insects.

• Stages of lyme disease:
1. Early localized - a skin lesion at the site of tick bite, called erythema chronicum migrans (ECM). It is a rash that spreads out over time. 
2. Early disseminated - smaller, multiple ECM on the body. Four organs can be invaded: 
• Brain and nerves: meningitis, cranial nerve palsies (especially Bell's palsy), and peripheral neuropathies. 
• Heart: transient heart blocks and less commonly, myocarditis. 
• Joint: brief attacks of arthritis. 
3. Late - chronic arthritis or chronic neurologic damage. 

Borrelia recurrentis
Transmitted to humans by body lice. The bacteria spreads in the blood, causing a high fever, headaches and muscle aches. Symptoms relapse due to antigenic variation of surface proteins exhibited by the bacteria.

Leptospira
Transmitted to humans who come in contact with animal urine. In the first phase of disease: high spiking fever, headache and severe muscle aches, and red eyelids. In the second, immune phase: meningitis.

Leptospira interrogans can cause the more severe Weil's disease, or infectious jaundice. It causes renal failure, hepatitis, jaundice and hemorrhages in many organs.