Bacteria

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Bacteria are single celled microorganisms, without a nucleus (prokaryotes), that can cause lots of morbidity and mortality. They are not infrequently seen by pathologists.

Actinobacteria

General

  • A very large group of bacteria.

It includes:[1]

  • Actinomycetes.
  • Corynebacterium.
  • Mycobacterium.
  • Nocardia.
  • Streptomyces.

Actinomycetes

General

Notes:

  • Mycete = fungus; these organisms have a fungus-like appearance.

Gross

  • Yellow granules.[3]

Microscopic

Features:[4][3]

  • Branching rods.
  • Typically form pink/purple granules ("sulfur granule") that is surrounded by inflammatory cells (lymphocytes or neutrophils).

DDx:

  • Nocardia.

Notes:

  • Sulfur granule may be seen grossly - yellow.[3]

Images:

Stains

  • Gram +ve.
  • AFB -ve.
    • Nocardia +ve.
  • PAS +ve.
    • May be confused with a fungus!

Helicobacter pylori

See Helicobacter gastritis.

Clostridium difficile

  • Commonly C. difficile.

General

  • Gram positive bacillus.

One virulent strain is:[5][6] BI/NAP1.

  • Deletion of tcdC locus.
  • Resistant to fluoroquinolones (gatifloxacin and moxifloxacin).

Chlamydia trachomatis

  • May be referred to as Chlamydia.

General

Note:

  • Often co-exists with gonorrhea.

Microscopic

  • Variable.

Lymphogranuloma venereum:

Mycobacterium tuberculosis

  • Abbreviated TB.

General

  • Causes tuberculosis.
  • May mimic a malignancy.
  • Strong association with HIV.

Clinical

Classic features - pulmonary/systemic:

  • Cough.
  • Fever.
  • Weight loss.

CNS manifestations:

  • Tuberculoma (mass).
  • Meningitis.
  • Abscess.

Tests:

  • PPD test, AKA Mantoux test, AKA TB skin test.

Treatment:

  • Multiple drugs for a long time (months).
    • Commonly used drugs: isoniazid, rifampin, pyrazinamide, and ethambutol.

Gross

Ghon complex

Consists of two components:[7][8]

  1. Peripheral focus - subpleural, calcified.
  2. Central focus - the hilar lymph node that drains the peripheral focus.

Image:

Microscopic

Features:

Note:

  • May be non-necrotizing.

DDx:

Images:

Stains

  • Ziehl-Neelsen stain - red rod-shaped bacteria - key feature.
    • Very small - must use 40x objective.

Image:

Molecular

  • Can be diagnosed with PCR.

Mycobacterium leprae

General

  • Causes leprosy.

Clinical:

  • Nerve damage -> injuries -> disability.

Microscopic

Features:

Stains

  • Fite stain - red rod-shaped bacteria - key feature.
    • Very small - must use 40x objective.

Images:

Mycobacterium avium complex

  • Abbreviated MAC.
  • Previously referred to as Mycobacterium avium-intracellulare, abbreviated MAI.

General

  • Refers to an infection with both:[11]
    • Mycobacterium avium
    • Mycobacterium intracellulare.

Microscopic

Features:

  • Small rod-shaped organisms - within histocytes.
  • +/-Granulomas.

DDx:

Stains

  • AFB +ve.

Coxiella burnetii

General

  • Causes: Q fever.

Features:

  • Intracellular bacterium.
  • Gram negative.

Clinical:

  • Flu-like symptoms.

Microscopic

Features:

  • Fibrin ring granuloma.
    • Epithelioid macrophages (i.e. a granuloma) surrounding a thin pink (fibrin) ring.

DDx:[12]

  • Infections (Coxiella burnetii, CMV, EBV + others).
  • Drug reaction.
  • Malignancy (e.g. Hodgkin lymphoma[13]).

Images:

Bartonella henselae

General

Causative agent in:

Microscopic

Features - bacillary angiomatosis:

Features - cat-scratch disease:

  • Stellate granulomas.

Stains

Image:

See also

References

  1. ↑ 1.0 1.1 Ventura, M.; Canchaya, C.; Tauch, A.; Chandra, G.; Fitzgerald, GF.; Chater, KF.; van Sinderen, D. (Sep 2007). "Genomics of Actinobacteria: tracing the evolutionary history of an ancient phylum.". Microbiol Mol Biol Rev 71 (3): 495-548. doi:10.1128/MMBR.00005-07. PMC 2168647. PMID 17804669. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2168647/.
  2. ↑ Humphrey, Peter A; Dehner, Louis P; Pfeifer, John D (2008). The Washington Manual of Surgical Pathology (1st ed.). Lippincott Williams & Wilkins. pp. 446. ISBN 978-0781765275.
  3. ↑ 3.0 3.1 3.2 URL: http://pathmicro.med.sc.edu/mycology/mycology-2.htm. Accessed on: 14 September 2011.
  4. ↑ URL: http://pathology.class.kmu.edu.tw/ch05/Slide42.htm . Accessed on: 14 September 2011.
  5. ↑ URL: http://www.medpagetoday.com/InfectiousDisease/PublicHealth/2254. Accessed on: 15 August 2011.
  6. ↑ McDonald, LC.; Killgore, GE.; Thompson, A.; Owens, RC.; Kazakova, SV.; Sambol, SP.; Johnson, S.; Gerding, DN. (Dec 2005). "An epidemic, toxin gene-variant strain of Clostridium difficile.". N Engl J Med 353 (23): 2433-41. doi:10.1056/NEJMoa051590. PMID 16322603.
  7. ↑ Rose, Alan G. (2008). Atlas of Gross Pathology with Histologic Correlation (1st ed.). Cambridge University Press. pp. 112. ISBN 978-0521868792.
  8. ↑ URL: http://pathhsw5m54.ucsf.edu/case32/image324.html. Accessed on: 27 February 2012.
  9. ↑ URL: http://www.medscape.com/viewarticle/576467_2. Accessed on: 2 January 2012.
  10. ↑ URL: http://www.meddean.luc.edu/lumen/MedEd/orfpath/bfsrinf.htm. Accessed on: 1 April 2012.
  11. ↑ Turenne, CY.; Wallace, R.; Behr, MA. (Apr 2007). "Mycobacterium avium in the postgenomic era.". Clin Microbiol Rev 20 (2): 205-29. doi:10.1128/CMR.00036-06. PMC 1865596. PMID 17428883. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1865596/.
  12. ↑ Tjwa M, De Hertogh G, Neuville B, Roskams T, Nevens F, Van Steenbergen W (2001). "Hepatic fibrin-ring granulomas in granulomatous hepatitis: report of four cases and review of the literature". Acta Clin Belg 56 (6): 341–8. PMID 11881318.
  13. ↑ de Bayser L, Roblot P, Ramassamy A, Silvain C, Levillain P, Becq-Giraudon B (July 1993). "Hepatic fibrin-ring granulomas in giant cell arteritis". Gastroenterology 105 (1): 272–3. PMID 8514044.
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