Miscellaneous bacterial pathogens
• Bacteria without cell walls
• Bacteria that require host cells
• Spiral and curved bacteria
• Some of these are related to Gram positives
and some are Gram negative, but all stain pink
in a Gram stain.
• Most are difficult or impossible to grow in the
lab.
1
Mycoplasma
2
• Mycoplasmas have unusual properties
– Very small, pleomorphic (cocci to filaments)
– Have no cell walls, but have sterols in their
membranes
– Require numerous growth factors to grow
• Species of interest: M. pneumoniae,
– M. pneumo attaches to epithelial cells, kills them
– Buildup of mucus, other infections
– Fever, malaise, sore throat, etc. walking pneumonia
– No cell wall! Can’t treat with penicillins
Mycoplasma-2
• Ureaplasma urealyticum
– Sexually transmitted, cause of urethritis
– Similar to M. pneumoniae, but urease +
– Other Mycoplasmas also cause NGU
• Non-gonococcal urethritis, infections caused by
something other than N. gonorrhoeae.
http://www.ai.mit.edu/people/tk/ce/mycoplasma-s.gif
3
Rickettsiae
• Gram negative, very small, obligate parasites
– Leaky membranes?
• Most diseases spread by vectors
• Rickettsiae infect endothelial cells lining blood
vessels, avoid digestion in lysozome
– Have LPS, generate fever
– Damage to capillaries produces spots, rashes
– Damage to vessels deprives organs of oxygen
4
Rickettsial diseases
• R. rickettsii: Rocky mountain spotted fever
– Spread by tick bite; rodents are the reservoir
– Most common through southeast, mid-south
• R. prowazekii: epidemic typhus
– Humans primary host; vector is the louse
– Disease spread in crowded, unhygienic conditions
• R. typhi: murine/endemic typhus
– present in rodent population, vector is the flea
5
Rickettsiae-2
• Ehrlichia chaffeensis- cause of 2 types of
ehrlichiosis.
– Similar to other rickettsial diseases, seldom rash
– Spread by lone star tick and dog tick
– Infects leukocytes rather than endothelial cells
– “emerging disease”, first identified by case at Fort
Chaffee, Arkansas.
6
Chlamydia
• Very small, obligate intracellular parasites
– Cell and outer membrane, but no peptidoglycan
• Spread directly rather than by vectors
• Two stage life cycle
– Elementary body: tiny (0.2-0.4 µm) and inert
• Spore-like: dormant and resistant
• Infectious: form that moves between cells
– Reticulate body: 0.6-1.5 µm, metabolically active,
reproduce inside host cells
7
Chlamydial diseases
• C. trachomatis: infects cells of mucous
membranes, conjunctiva. Mostly eye & STD
– Infection kills cells, stimulates inflammation which
also causes cell destruction
• Trachoma- leading cause of non-traumatic
blindness. Caused by certain strains.
– Infection of conjunctiva causes scarring, turning in
on eyelashes which scratch cornea.
– Scarred cornea, with ingrown blood vessels,
obscure vision.
– STD strains can also infect eyes, self-inoculation.
8
Sexually transmitted Chlamydial disease
• Non-gonococcal urethritis, about 50% of cases
• Chlamydia infections are the most common STD, but
even more are infected and asymptomatic
• Lymphogranuloma venereum
– Lymph nodes in genital region (inguinal) become
enlarged (buboes), may even rupture.
– Blocked lymph ducts lead to genital elephantiasis,
other damage in genital region.
– 85% of women asymptomatic; others can develop
PID; scarring of uterine tubes can lead to sterility,
ectopic pregnancy.
• Eye infections of newborns prevented with antibiotic
drops.
9
Spirochetes
10
• Spirochetes: teeny weeny squiggly things
– Have internal flagella in bundles called axial
filaments; corkscrew through liquid
• Treponema pallidum: cause of syphilis, STD
– Initial stages: chancre, hard, painless genital ulcer
following long incubation
– Ulcer disappears, spirochete spreads, causes
systemic disease (rash, fever, etc)
– Either goes away, comes back, or tertiary syphilis in
which gummas form; serious stage.
Spirochetes-2
• Borrelia burgdorferi: cause of Lyme disease
– Reservoir in rodents, deer; spread by deer tick
– Slow developing; fever, usually bulls-eye rash;
arthritis and heart or CNS involvement.
• Borrelia recurrentis: cause of relapsing fever
• Leptospira interrogans: cause of leptospirosis
– From contact with animal fluids, esp. urine.
– Infects liver and kidneys, from kidney enters urine
– Note: tidy cycle of spread and infection
11
Gram negative curved rods
12
• Vibrio: comma shaped
– Like enteric but oxidase positive; polar flagella
– Halotolerant to halophilic, grow in estuarine and
marine environments
– V. cholerae: cause of cholera
• Toxin-mediated severe diarrhea
• Salt, fluid leave intestinal cells, patient dies of
dehydration.
• Oral rehydration therapy (ORT): water, salts, and
glucose, now saving lives.
• Causes pandemics that spread around the world
– Lack of adequate sewage treatment
Other curved rods
• Campylobacter jejuni: number one cause of
bacterial gastroenteritis; zoonotic
– More common than Salmonella and Shigella
combined for food borne disease.
• Helicobacter pylori: cause of ulcers
– Correlated with stomach cancer.
– Produces urease enzyme
• Released ammonia neutralizes stomach acid,
irritates stomach lining.
• Basis for radioactive urease test.
13