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

Incidence of RMSF - 2002

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

Louse (lice) life cycle

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

Chlamydia psittaci

• c.a. of psittacosis• Produces atypical

pneumonia• Transmitted by

infected psittacine birds to humans or to poultry plant workers

• Parrots quarantined prior to sale