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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.
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Mycoplasma 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
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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.
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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
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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
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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.
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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 ( µm) and inert Spore-like: dormant and resistant Infectious: form that moves between cells Reticulate body: µm, metabolically active, reproduce inside host cells
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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.
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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.
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Spirochetes 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.
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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
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Gram negative curved rods
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
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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.
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