Microbiology

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Author:
grignoter
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162701
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Microbiology
Updated:
2013-03-16 13:55:05
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microbiology pathology medicine
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microbiology
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  1. Septic arthritis - causative organism
    19 - 30yo commonest is Neisseria gonnorhoea, the arthritis occurs after an asymptomatic period. Take a sexual history in a young person with a single inflammed joint!
  2. Gram Negative Bacteria
    - appearance
    Red/pink

    • Do not retain crystal violet as outer membrane prevents it getting in
    • Retain safranin (red)

    • Have 2 membranes:
    • 1. cytoplasmic membrane
    • ------ thin peptidoglycan layer
    • ----- periplasmic space
    • 2. outer membrane containing LPS and porins
    •       LPS includes lipid A, a core polysaccharide and the O Ag
  3. Gram Negative Bacteria
    - characteristics
    • more antibody resistant (impenetrable wall)
    • pathogenesis may be associated with cell envelope especially LPS (endotoxin) layer- LPS --> cytokines --> inflammation
    • don't sporulate (except Coxiella burnetii)
  4. Gram Positive
    Purple

    Retain crystal violet after washing
  5. Enteric Fever
    • salmonella typhi (G-)
    • salmonella paratyphi

    Incubation: 21d or less

    Clinical: stepwise temperature increase, malaria has been excluded, abdo symptoms, relative bradycardia (expect heart rate to increase by 15bpm for each degress above 37ish so tachycardia expected if pyrexial. 80 - 90 therefore = bradycardia).

    "Rose Spots"= 2 - 3mm pale pink spots, mainly on torso

    "pea soup" diarrhoea or constipation.

    Investigations: blood and stool cultures diagnostic. EXCLUDE MALARIA.

    Sequelae: GI perforation, bleeding
  6. Salmonella typhi
    gram negative

    Transmission: faecal-oral

    • Enteric Fever.
  7. Hepatitis A
    Incubation: 2 - 6 weeks

    Clinical: flu-like prodrome (2 weeks), icteric hepatitis (2 weeks - 3 months). May be asymptomatic in <5yo

    Transmission: faecal-oral (sometimes sexual, especially in MSM)

    Outcome: moratlity ~1-%, increased in >40yo, CLD, HepB or C or EtOH

    • Investigations:
    • 1. hepatitic biochemistry (high AST/ALT, BR, mildly high ALP)
    • 2. IgM anti-HAV using EIA

    Management: symptom control, rest, hydration, outpatient care. May give Ig or HAV vaccine to contacts.
  8. Biochemisty of Acute Viral Hepatitis
    ALT and AST 500 - 10,000 IU/L in first few weeks

    BR 30 - 100 umol/L, conj and unconj and bilirubinuria

    ALP <300IU/L

    PT 1 - 5 seconds prolonged. (>5s suggests impending hepatic failure)
  9. Hepatitis B
    Transmission: global majority acquired vertically. Efficient sexual transmission.

    • Clinical: asymptomatic in children and immunosuppressed. ~30% icteric, can --> fulminant hepatitis, cirrhosis, and hepatocellular cancer.
    • 1% get fulminant hepatitis - decompensated liver disease, 50% mortality.

    10% get chronic HBV (antigen + for >6mo), typically asymptomatic until cirrhosis and decompensated liver disease - ascites, jaundice, varices, confusion, cachexia, death.

    10% with cirrhosis --> Ca (enlagring liver, weight loss, death).

    • Investigations:
    • 1. hepatitic biochemistry when acute (high AST/ALT, BR, mildly high ALP) OR mildly high AST/ALT when chronic
    • 2. Worsening LFT and PT if cirrhosis or Ca
    • 3. Serology - sAg proves infection. e and c are also useful and DNA is the most sensitive assay. NB. some mutations give HBeAg negative active infection (pre-core mutations).

    Management: symptom control, fluids, rest. Lamivudine, adeofovir, inteferon. Liver transplant (if cirrhosis/Ca).
  10. Hepatitis B Serology
    sAb = antibodies against the surface - positive with any exposure, incluidng infection and vaccination

    eAb = antibodies against the core - positive in anyone who has had replicating virus in them - infected, chronic, carrier, and had previously but now cleared.

    sAg = surface antigen - positive if currently have virus or recently vaccinated

    eAg = core antigen - positive if currently replicating virus in the system - infected and infectious

    HBV-DNA = DNA of the virus, positive if currently replicating virus in the system - infected and infectious
  11. Hepatitis D (delta)
    RNA virus, only occurs as co-infection with HBV

    Transmission: sexual, IVDU. Acquired with acute HBV or as superinfection during chronis HBV. (May get two acute bouts of virus.)

    Incubation: 3 - 7 weeks

    • Clinical: 10x more likely to be fulminant, 80% fatal.
    • When + acute HBV: severe icteric hepatitis (--> chronic in 80%). More rapid progression to cirrhosis and Ca.

    Investigations: serum anti-HDV (antigen and RNA tests also possible)

    Management: no effective antivirals. HBV vaccination and protective behaviour.
  12. Hepatitis C
    Transmission: IVDU, vertical (esp is HIV coinfection), some sexual (esp if HIV)

    Incubation: 150 days

    Clinical: ~20% are icteric, mainly asymptomatic. Fulminant rare unless HAV superinfection. 80% --> chronic HCV. ~20% develop cirrhosis 20 years later. 5% develop Ca 20 - 30 years later. Cirrhosis more likely and more rapid with HIV, HBV or EtOH.

    Investigations: Ab assays (may be negative for first 9 months). ELISA for screening, RIBA for confirmation. PCR.

    Management: no vaccine. Education and prevention. Vaccinate for HAV and HBV. pegylated inteferon injections + 6 - 12mo of ribavirin is curative for 50% (expensive).
  13. Chlamydia trachomatis
    • gram negative
    • obligate intracellular cocci

    • 3 human biovars:
    • -- Ab, B, Ba, C = trachoma in the eyes
    • -- D - K = STI cervicitis, urethritis, PID, neonatal pneumonia and conjunctivitis
    • -- L1 - L3 = LGV
  14. Symptoms of Chlamydia
    • discharge
    • post-coital bleeding
    • dysuria (especially in men)
    • mucopurulent discharge in men
    • pelvic pain
    • cobble-stone appearance of cervix
    • 50% women and 80% men aysmptomatic
    • 2 week incubation
  15. Sequelae of Chlamydia
    • salpingitis, PID
    • infertility
    • subsequent ectopic pregnancy
    • perihepatitis (if ascends into abdomen)
    • epididymitis
    • conjunctivitis (neonatorum)
    • Reiter's disease
  16. Fitz-Hughes-Curtis Syndrome
    ascending chlamydia enters the abdomenal cavity and causes perihepatitis??
  17. Diagnosis of Chlamydia
    • urine antigen detection
    • vaginal swab culture
    • NAAT?
  18. Management of Chlamydia
    • doxycycline
    • contact tracing
  19. Lymphogranuloma Venerum (LGV)
    • Chlamydia trachomatis
    • L1, L2, L2a or L3
    • infects lymphatics then monocytes
    • commoner in MSM
    • commoner in HIV infection
    • primary stage: painless ulcer
    • secondary: buboes and lymphangitis
    • tertiary: fibrosis and long-term oedema
  20. LGV - Primary Stage
    • painless genital ulcer 3 - 12 days after infection
    • self-resolving, often goes unnoticed
    • 10% get Erythema Nodosum
  21. LGV Secondary Stage
    • 10 - 30 days after primary stage
    • unilateral buboes - inflammed LN in groin
    • lymphangitis, e.g. dorsal penis (cord-like)
    • proctitis or proctocolitis
    • cervicitis, perimetritis, salpingitis
    • fever, malaise, anorexia
  22. Buboes
    • painful enlarged inguinal LN
    • inflammation --> thin skin, fixation
    • progress to: necrosis, flutuant/suppurative LN, abscess, fistula, stricture, sinus tract, fibrosis obstructing lymphatics, chronic oedema
  23. Symptoms of Proctitis
    (distal 10 - 12cm)
    • anorectal pain
    • tenesmus
    • rectal discharge
  24. Symptoms of Proctocolitis
    (>12cm from anus)
    • anorectal pain
    • tenesmus
    • rectal discharge
    • diarrhoea
    • abdominal cramps
  25. Reiter's Disease
  26. Malaria
    • Plasmodium: falciparum (deadliest), vivax, ovale, malariae
    • Protazoan

    • Falciparum has most cases in UK and increasing.
    • Malaria is 22% of the cases of fever in the returning traveller in the UK

    Endemic Areas: subsaharan African (incl Ghana, Nigeria, Kenya), India, Southeast Asia, Central America and the northern part of South America

    • Clinical: fevers and rigors (acute phase response), flu-like syndrome, cough, diarrhoea, jaundice
    • NB. not typically rash or lymphadenopathy

    Clinical differentials may include: flu, URTI, gastroenteritis, hepatitis

    • Investigations:
    • - blood film: thick blood film shows plasmodium, thin film shows subtype. 3 may be needed 24 h apart. Not diagnostic if patient is on semi-immunosuppressant levels of antimalarials.
    • see "ring form" of RBC containing small parasite that has an eosinophilic nucleus, basophillic cytoplasm and a vacuole in the middle. Classify parasitaemia as % of the RBC on the film containing parasites.
  27. Dengue Fever
    increasing prevalence

    Endemic Areas:
  28. Rabies
    • lyssa virus
    • an enveloped ssRNA with negative sense
    • family: rhabdoviridae

    Transmitted by bats, monkeys, cattle

    Pathology: travels up peripheral nerves, incubation depends on distance to travel
  29. Rabies - Signs and Symptoms
    Early: malaise, headache, fever (early encephalitis)

    Mid: acute pain, violent movements, slight or partial paralysis, mania, depression, hydrophobia, hypersalivation, paranoia, hallucinations. Sometimes inflammation of spinal cord → transverse myelitis.

    Late: mania, lethargy, confusion, coma, renal failure
  30. Rabies - Investigation and Management
    Ix: hx, examine animal which bit, Negri inclusion bodies (eosinophilic, sharp outlines in cytoplasm of neurons, they are proteins produced by the virus)

    • Management:
    •       1. Thoroughly wash wound (reduces number of viral particles) - iodine or alcohol, or flush mucus membranes with water
    •       2. If no pre-exposure vaccine: Human Rabies Immunoglobulin (1 dose) <20U/kg - around bite as much as possible, the rest as deep IM in
    • distant site
    •      3. rabies vaccine (4 doses over 14 days) PEP within 10 days can be up to 100% effective.

    BUT rabies is usually fatal (respiratory insufficiency) once neuro symptoms begin.
  31. ELISA
    Enzyme-linked immunosorbent assay

    • 1. Sample Ag applied to surface
    • 2. Ab-enzyme complex to this Ag applied
    • 3. Enzyme's substrate is added

    Reaction  colour change
  32. Trichomonas Vaginalis
    • flagellated protazoan
    • invades superficial epithelium of urogenital tract
  33. Symptoms of Trichomonas Infection (females)
    • offensive, frothy, greeny-grey discharge
    • dyspareunia
    • dysuria
    • vaginits
    • vulvitis
    • strawberry cervix (punctate erythema)
    • (asymptomatic in males)
  34. Management of Trichomonas Vaginalis
    metronidazole
  35. Neisseria Gonorrhoeae
    • gram negative diplococcus
    • infects mucosal surface of genito-urinary tract, rectum and pharynx
    • typically asymptomatic
  36. Complications of Gonnorrhoea
    • Bartholin's abscess
    • salpingitis +/- irreversible tubal damage
  37. Symptoms of Gonorrhoea (males)
    • dysuria
    • frequency
    • mucopurulent discharge 3 - 5d after exposure
    • urethritis
    • meatal oedema
    • (females usually symptomatic)
  38. Disseminated Gonnococcal Infection
    • <1% cases
    • pyrexia
    • vasculitic rash
    • polyarthritis
    • managed with antibiotics (culture for sensitivity)
  39. Bacterial Vaginosis
    • mixed anaerobic flora
    • may include Gardnerella vaginalis, Mycoplasma hominis
    • creamy grey discharge
    • fishy odour
    • no itching
    • risk of preterm delivery and late miscarriage if present in pregnancy

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