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Bergey’s “oddball”Gram negatives
*Obligate intracellular parasites:
Rickettsia
Chlamydia
*Bacteria lacking cell walls:
Mycoplasma
Spiroplasma
Rickettsia and Chlamydia
• Almost all are obligate intracellular parasites grow and reproduce only in host cells
• Metabolically incomplete they cannot synthesize all necessary metabolic molecules
• Resemble viruses (small size and intra-cellular requirement for reproduction)
Rickettsia• ca of RMSF, typhus
and others• Transmitted by blood
sucking arthropod (tick, flea, louse)
• Animal or insect reservoir
• Infects endothelial cell – produces vasculitis/ vascular obstruction -> producing small hemorrhages -> rash
Rocky Mt Spotted Fever • ca is R. rickettsia • Found in young people• Transmitted by ticks• Most cases east of Miss!• Misdiagnosed as measles• Case fatality rate is high• Treat with chloramphenicol• Death due to:
– Hypotension
– Intravascular coagulation
Epidemic typhus
• typhus = “stupor”• c.a. is R. prowazekii• Transmitted by body
lice – typically among crowded populations
• High prolonged fever• Vasculitis/coagulation• Vaccines available for
military
Endemic typhus (found in US)
• c.a. is R. typhi• Usually not fatal• Rat flea vector• Rodent reservoir• Sometimes referred to
as “murine typhus”
Chlamydia
• Important pathogen in humans and animals• Includes two morphological types within its
life cycle– Elemental body = infectious form; attaches to
cell surfaces – stimulates phagocytosis– Reticulate body = reproductive form; acquires
host ATP, divides within and kills host cell
Diagnosed as “inclusion bodies” within epithelial cells
Chlamydia trachomatis I• c.a. of most common STD
(4 million/yr) in the U.S.
• Produces NGU
• Can be self-limiting
• Sensitive to antibiotics
• Males – purulent urethral discharge
• Females – many asymptomatic
• Can lead to PID in women
• Opthalmia neonatorum to neonate
Chlamydia trachomatis II
• Lymphogranuloma venereum (LGV)
• Caused by strains of Ct that invades and infects lymphoid tissue
• Enlarged local lymph nodes
• Esp. near genital area
Chlamydia trachomatis III• “trachoma” = #1 cause
of blindness worldwide• ~500 million affected• Transferred by flies,
infected fingers, infective discharges on bedding, pillows, etc.
• Damage to cornea invites secondary infection blindness
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