Term
| How do Neisseria meningits and HACEK organisms switch from colonizing to pathogenic etiologies? |
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Definition
1) Neisseria that colonizes the pharynx of one individual can pass to a new host with no adaptive immunity to it, resulting in inflammation and life-threatening bacterial meningitis
2) HACEK organisms (Haemophius parinfluenzae, Aggregatibacter spp, Cardiobacterium hominis, Eikenella corrodens and Kingella kingae) stick to fibrin-platelet thrombi on damaged heart valves and can cause infective endocarditis. |
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Term
| Define Koch's postulates of microorganism involvement in infectious disease |
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Definition
1) Must be found in organisms suffering from disease but not in healthy individuals (Clostridium difficile violates)
2) Must be isolated and grown in pure culture (Viruses and prion diseases violate)
3) Cultured organism must cause disease when introduced to naive individual
4) Must be able to re-isolate from diseased experimental host and identify as same organism |
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Term
| What are some examples of "Qualitative" microbiological testing and what are pros/cons? |
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Definition
1) Blood cultures, acid fast bacillus cultures from sputum for TB
2) Maximize sensitivity at expense of PPV (many false positive from contamination) |
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Term
| What are some examples of "Semi-quantitative" microbiological testing and what are pros/cons? |
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Definition
Perform this test to decide whether isolated organism is colonizing/contaminating only, or whether it can be responsible for inflammation.
1) Examples include wound cultures and sputum cultures
-Directly stain specimen (Gram, AFB, calcoflour)- you need 10^6 per mL to visualize.
- Plate and follow for 3-5 days |
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Term
| How do "Quantitative" microbiological tests work and what are some examples? |
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Definition
1) Use a predetermined CFU/mL cut-off to determine whether organism could be cause of inflammation
2) Urine cultures (UTI > 10^5), Bronchoscopic lavage cultures, skin biopsy cultures from burn patients |
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Term
| What are some uses of blood (serum) cultures for microbiological diagnosis? |
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Definition
Remember, take 2 samplings from 2 different sites.
1) Fungal or parasitic antigens (Cryptococcus, Aspergillus, Malaria)
2) Direct microscopy (malaria, Babesia)
3) Antibody detection
4) Detection of viral RNA or DNA genomes by PCR (HIV, CMV) |
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Term
| What should you look for in a typical urine culture to distinguish infection from contamination? |
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Definition
1) WBC count and >100,000 bacteria/mL (infection)
2) Presence of epithelial cells or multiple bacterial types (contamination)
Can also use urine test for bacterial and fungal antigens, and well as viral genomes (BK virus in kidney transplant). |
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Term
| What should you look for in a typical CSF sample? |
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Definition
Do a lumbar puncture and perform
1) Gram stain for bacteria
2) India ink dye to look for Cryptococcus neoformans (fungus)
3) PCR to look for virus (HSV) |
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Term
| How do you obtain a Respiratory tract sample of sputum? |
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Definition
Broncho-alverolar lavage (BAL) to avoid contamination
Use swabs instead for Pertussis and Influenza. |
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Term
| What should you look for in a typical stool sample? |
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Definition
1) Microscope for GI parasties
2) EM for viruses
3) Culture for bacteria and to PCR look for toxins (C. difficile). |
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