Unit 3 Organisms – Flashcards
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| Mycobacteria (general) |
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| Non-motile, Non-spore-forming Obligate aerobes Slender bacilli Unusual cell walls: contain mycolic acid, high lipid content - renders them hydrophobic and highly resistant to drying/disinfectants/pH changes Slow growing with fastidious growth requirements (supplement agar with homogenized eggs and other complex media - Lowenstein-Jensen Agar); heat-sensitive (kill with pasteurization) Stain with special dyes (Kinyoun and Auromine O) - acid fast ("red snappers") Broken into groups - tuberculous group and Runyon groups 1-4 |
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| Tuberculous Mycobacteria (M. tuberculosis, M. bovis, M. africanum) |
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| All cause tuberculosis; acquired via inhalation of droplet nuclei (or through GI tract or abraded skin) M. tuberculosis: organisms enter respiratory tract in droplets and are phagocytized by alveolar macrophages; then prevents fusion of phagosome with lysosome -> macrophages/lymphocytes attracted by chemotactic factors -> multinucleated giant cells (Langhans cells) -> granulomas to prevent disease spread M. tb = most common cause of infection in HIV patients |
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| Tuberculosis |
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| Screen for TB with PPD and Quantiferon-TB Gold assay Primary disease - pulmonary tract, insidious onset with nonspecific complaints, sputum production May remain dormant in 90% See evidence on CXR (upper lobes), positive PPD, lab detection by smear/culture(red snappers)/PCR Screen for MDR genes with PCR Treat with triple therapy for pulmonary disease - rifampin, isoniazid, pyrazinamide (6 months) Skin converters - INH and PZA (9-12 months) Prevention: N95 mask, negative pressure room with airborne precautions (consider pt non-infectious after 3 consecutive days of negative sputum samples) |
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| Mycobacterium avium complex (MAC) |
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| M. avium + M. intracellulare Environmental organism (water, plants, soil) Causes pulmonary disease in immunocompetent and immunocompromised (i.e. HIV) patients |
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| Mycobacterium marinum |
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| Causes fish tank granulomas |
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| Mycobacterium fortuitum Mycobacterium chelonae Mycobacterium abscessus |
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| Rapid growers Associated with cutaneous and subcutaneous infections, and prosthetic device/indwelling catheter infections |
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| Mycobacterium leprae |
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| Cannot grow unless in an animal model 2 presentations: tuberculoid leprosy (skin hypopigmentation; in immunocompetent hosts), and lepromatous leprosy (immunocompromised; presents as nodular disfigurement of skin) Transmitted via direct contact Detect organisms in skin scrapings (best from earlobe) Treatment: simple and inexpensive - sulfa drug dapsone |
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| Nocardia |
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| Hybrid organism: gram + and mycobacterium properties (can stain gram + or partially acid fast) Produces long, branching, thin filaments (has a pink, beaded appearance) Found in the soil - causes pulmonary infection from inhalation or infection through abraded skin See abscesses that follow lymphatics Treat with bactrim |
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| Spirochetes |
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| Treponema - 3 species, cause 3 different diseases Borrelia - several species causing endemic, epidemic relapsing fevers and lyme disease Leptospira interogans: leptospirosis Spiral shaped, actively motile (periplasmic flagellum) |
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| Treponemes |
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| All are spiral shaped, obligate anaerobes, can't be gram stained or cultivated in vitro; visualize with silver stain Acquired through abraded skin/wounds, produce primary skin lesion, produce similar antibody responses All respond to PCN |
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| Treponema pertenue |
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| Yaws/Frambesia Endemic to tropics, spread by direct contact 3-4 wk incubation period Primary lesion: Mother Yaw -> will produce secondary Yaws in 6-15 wks Tertiary yaws - gummatous nodules or deep chronic ulcerations |
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| Treponema carateum |
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| Pinta Endemic to Central/South America Transmitted via direct contact Get a nonulcerating primary lesion -> develops into hyperpigmented lesions on hands, feet, scalp (may become depigmented after several years) Tertiary manifestations rare |
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| Treponema pallidum |
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| Syphilis Transmitted by direct, usually sexual, contact Organisms spread through lymphatics and systemic circulation -> hard chancre/primary lesion develops at site of inoculation = highly infectious, lots of spirochete shedding (when baby is most at risk for congenital syphilis) Pattern of dormancy and symptomatic periods - first get chancre and general illness signs, then latency, then rash and flu-like symptoms, then latency, then tertiary presentation for 1/3 of infected (gummatous skin lesions, aortic aneurysm, CNS symptoms, MR) Serodiagnosis based on screening for nonspecific antibodies - if they're present, go to confirmatory screening Also have EIA screening |
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| Congenital Syphilis |
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| Spread of disease caused by treponema pallidum from infected mother to fetus First trimester: treponema cannot cross placenta - fetus is safe and mother can get treated 2nd and 3rd trimester - if mother has primary or secondary disease, baby will be stillborn; if tertiary disease, baby will have congenital defects |
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| Borrelia |
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| Visualized with aniline dye (Wright, Giemsa) Microaerophilic, can be cultivated in vitro Helical shaped (spirochetes) Arthropod borne infections Difficult to grow (need special media) |
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| Borrelia recurrentis |
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| EPIDEMIC relapsing fever Spread to human by spirochete on body louse Borrelia live in hemolymph of louse -> transmitted when human squish louse (itchy!) and release the infected hemolymph into their abraded skin; penetrate into skin using cork-screw motility Associated with poor hygiene Cause relapsing fever due to antigenic variation during course of infection - associated with changes in outer membrane protein (variable major protein) Diagnose with peripheral blood smear, treat with PCN or tetracycline; avoid arthropod vectors! |
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| Borrelia hermsii/parkeri/etc (Endemic Relapsing Fever) |
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| Borrelia enter hemocele of ticks and then disseminate into all tissues -> spread to human when infected ticks bite (spirochetes in salivary glands) Ticks normally also infect rodents and rabbits Cause relapsing fever due to antigenic variation during course of infection - associated with changes in outer membrane protein (variable major protein) Diagnose with peripheral blood smear, treat with PCN or tetracycline; avoid arthropod vectors! |
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| Lyme Disease |
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| Associated with Borrelia burgdorferi, transmitted by female Ixodes hard shell ticks See a primary skin lesion (erythema migrans) or "bullseye" rash in some -> spirochetemia at site of first infection, then becomes a relapsing/remitting couse -> late stages are worse: arthritis, CNS involvement, cardiac, skin effects Prevalent in NE, Michigan, Wisconsin and parts of California; endemic on Long Island, CT Increased cases in summertime - prevent by wearing protective clothes outdoors (esp. hiking and hunting) and checking self for ticks (remove immediately - need 36 hours to get disease); used to be a vaccine but it wasn't effective Deer Tick -> Mice, Deer (Humans not part of natural cycle) Difficult to diagnose - no good test so use clinical suspicion Rx: PCN, tetracycline in early stages; ceftriaxone in late stages |
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| Leptospira interrogans |
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| Spirochete veterinary pathogens that cause kidney infections in animals (humans are not reservoir or primary host) Infected animals excrete leptospira in urine -> humans with occupational exposure at risk (vets, sewer workers) Causes conjunctival hemorrhage, kidney infections in humans Diagnosis: urine sample (also blood and CSF), use PCR Rx: PCN, tetracycline |
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| Anaerobes (general) |
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| Colonize the human body: skin 10:1, mouth and UG tract 100:1, colon 1,000-10,000:1 Cannot grow in presence of oxygen because they lack superoxide dismutase (killed by free radicals) Injuries that predispose to intoxification/toxemia: things that reduce perfusion, trauma (GSW, surgery, bowel perforation), metabolic/pathologic processes (diabetes, tumors) Usually have foul smelling infections Overwhelmingly, infections are from endogenous sources Rx: always debride wound and give appropriate antibiotics |
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| Gram - Non-spore forming Anaerobes |
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| Fusobacterium (spindle shaped) Bacteriodes fragilis Prevotella melaninogenica (form black colonies) Virulence factors: adhesins (capsule, fimbriae), superoxide dismutase, catalase, IgA/M/G proteases, tissue destructive enzymes (hemolysin, phospholipase C, heparinases, lipases, collagenases, proteases) Above diaphragm: use PCN (fusobacterium, prevotella, etc) Below diaphragm: bacteriodes fragilis - PCN resistant so use something else |
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| Propionobacterium acnes |
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| Anaerobic gram + rod Causes acne (normal skin flora) |
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| Actinomyces |
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| Anaerobic, gram + rod (Similar morphology to Nocardia - branched) Normal flora of mucous membranes, causes subcutaneous infection, prosthetic-device-related infection, IUD infections, cervical facial infection (Lumpy Jaw), thoracic/abdominal/pelvic infections See sulfur granules (yellow) upon microscopic exam Rx: surgical debridement, PCN (or clindamycin or erythromycin) |
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| Mobiluncus |
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| Anaerobic, gram + curved rod Normal flora of vagina - second leading cause of vaginosis (watery discharge, fishy smell) Rx: ampicillin, clindamycin or erythromycin |
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| Clostridia vs. Other Anaerobes |
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| Clostridia - have exotoxins, most infections are monobacterial Other Anaerobes - no exotoxins, polymicrobic infections (some aerobes too) Both: cause toxemias or intoxifications |
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| Clostridium perfringens |
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| Causes gas gangrene and myonecrosis Exogenous (soil) and endogenous (bowel) reservoirs Toxins: alpha (phospholipase C causes intravascular hemolysis), beta (necrotizing), neuramidase (capillary thrombosis), enterotoxin (alters ileal membrane permeability, food poisoning) Presentation: predisposing trauma, local edema, crepitus, bullae, pain, cherry red urine (hemoglobinuria from phospholipase C) Dx: gram stain shows gram + rods (no spores) Rx: surgical drainage and debridement, PCN |
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| Clostridium difficile |
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| Gram + anaerobe, causes antibiotic-associated (clindamycin, cephalosporins, oxacillin, PCN) diarrhea and pseudomembranous colitis Normal flora of bowel, also in hospital environment (nosicomial); causes a superinfection Cannot grow in lab; use EIA or PCR At risk: abd surgery, intestinal obstruction, antibiotics/antineoplastic agents Toxins: A (enterotoxin, causes fluid loss), B (cytotoxin, destroys colon mucous cells); hypervirulent strain cannot turn off toxin production (20-30x more toxins) Rx: metronidazole, vancomycin (may see pt relapse), stool donor replacement therapy |
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| Clostridium botulinum |
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| Botulism - acute, often fatal; from ingestion of preformed toxin in improperly processed canned food Toxins -> absorbed in GI tract and block release of Ach in nerve terminals -> target diaphragm = respiratory paralysis (very lethal toxin at low dose) Medical emergency, treat with specific antitoxin (need lab to serotype) Prevention: boil foods for 10min, proper food processing Also have infant (may cause SIDS), wound (same as foodborne), inhalation (bioterrorism) botulism |
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| Clostridium tetani |
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| Tetanus/Lockjaw - acute disease produced by neurotoxin at site of localized infection Organism common in GI tract, soil Local infection -> exotoxin absorbed -> ascends along nerves -> suppresses inhibitory neurons -> excitability and rigidity without direct stimulation of synapses S+S: headache, irritability, muscle stiffness, masseter spasm, dysphagia, rigidity (backward arching - opsithothonus) Dx: clinical, site of infection usually not evident (do try to locate and debride wound) Rx: human tetanus immune globulin, PCN Prevention: tetanus booster every 10 years |
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| Legionella |
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| 3 outcomes: asymptomatic infection, Pontiac Disease, Legionnaire's Opportunistic human pathogen - usually live in water, can grow in stagnant warm water in cooling towers, hot tubs, etc -> exposure with inhalation/aspiration of organisms -> Taken up by macrophages/monocytes -> alters endosome so it can't merge with lysosome -> replicates and escapes NOT CONTAGIOUS (outbreaks from contaminated areas, not people - think of travel) Rx: antibiotics (infection can be lifethreatening) - fluroquinolones, doxycycline, azithromycin + rifampin Dx: urine antigen test + culture of respiratory secretions Healthcare outbreaks common - susceptible people + old plumbing |
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| Chlamydia (General) |
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| Unusual replication: elementary bodies (small, rigid outer membranes, rugged) bind to receptors and are endocytosed where they prevent binding with lysosome and are unpacked into reticulate bodies (noninfectious, intracellular form, replicating, fragile, make own DNA/RNA but need host ATP) Obligate intracellular parasites Inflammatory response may produce some symptoms, but does not clear infection For all patients that can't be treated with doxycycline, be sure to follow up and test to be sure treatment is working! |
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| Chlamydia trachomatis |
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| 18 serovars - serovar determines what symptoms/manifestation you have: Serovars A-C: Blinding Trachoma (infectious eye disease where eyelids turn inward and eyelashes scratch cornea) Serovars L1-L3: Lymphogranuloma venereum (small ulcer proceeds to painful, swollen lymph nodes - get buboes) Serovars D-K: Genital Chlamydia Genital Chlamydia - often asymptomatic (leads to PID in women), at risk with nonbarrier contraception/multiple sexual partners/socioeconomic disadvantage Risk for Reiter syndrome (arthritis, urethritis, eye problems) With women: easily inducible endocervical bleeding and discharge With men: urethral discharge, dysuria TEST FOR CO-INCIDENT CHLAMYDIA IN ALL STD PATIENTS! Dx: cytologic (Giemsa, IF), cell culture (tissue culture, a must for all legal cases), RNA hybridization with DNA probe (simple and fast), PCR, ELISA Rx: doxycycline - not for children or in pregnancy (use erythromycin, amoxicillin) Always treat sexual partner too - prevent spread. Use condoms to prevent. |
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| Chlamydia Pneumonia |
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| 3 organisms: C. pneumoniae: human to human, by respiratory secretions (adult community acquired pneumonia), usually mild illness (headache, sinus percussion tenderness, rhonchi/rales) C. psittaci: zoonosis from infected birds (rare), can be very serious/fatal (Horder spots, CP, splenomegaly, encephalitis, endocarditis, meningitis); not cultured (hazardous) C. trachomatis: spread from infected mother to infant, resulting in conjunctivitis and pneumonia in newborn, mild illness, may be seen rarely in immunocompromised adults Rx: C. pneumoniae and C. psittaci, use doxycycline or erythromycin; C. trachomatis, use erythromycin |
