Spirochaetes, Mycoplasma, Rickettsia and Chlamydia

Key points

• • These are atypical bacteria that do not behave like ordinary ones, so they need special methods to see, grow or detect them.
• • Spirochaetes are thin, coiled, motile bacteria; Treponema causes syphilis, Leptospira causes leptospirosis, and Borrelia causes Lyme disease and relapsing fever.
• • Mycoplasma are the smallest free-living bacteria and have no cell wall, so they are not seen on a Gram stain and cause an atypical (walking) pneumonia.
• • Rickettsiae are tiny obligate intracellular bacteria, spread by insect and tick bites, that cause the typhus and spotted fevers.
• • Chlamydiae are also obligate intracellular bacteria with a two-stage life cycle, and they cause eye infections (trachoma) and a common sexually transmitted infection.
• • Because they lack a normal cell wall or hide inside cells, several of these bacteria are missed by the tests that work on ordinary bacteria.