Miscellaneous bacterial pathogens

1. 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.

2. 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

3. 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

4. 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

5. 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

6. 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.

7. 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

8. 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.

9. 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.

10. 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.

11. 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

12. 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

13. 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.