Term
| How do Neisseria meningits and HACEK organisms switch from colonizing to pathogenic etiologies? |
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Definition
| ) 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 (Vibrio cholerae, Salmonella (typhoid Mary),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
| Microbiologic testing in clinical bacteriology practice • Qualitative |
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Definition
| (negative or positive) Patient specimen placed in nutritive broth to amplify small number of organisms present – Result is expressed as negative or positive for ___ – Finalizing negative results takes from 5 to 42 days depending on growth rate of organism – Mostly reserved for analysis of sterile body sites (blood, CSF) – Maximize sensitivity at the expense of positive predictive value (false positives from contamination are common) Examples: blood cultures, acid fast bacillus cultures from sputum for Mycobacterium tuberculosis |
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Term
Microbiologic testing in clinical bacteriology practice
-Semi-quantitative |
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Definition
(negative/rare/light/moderate/heavy growth)
– Specimen directly stained (Gram stain, AFB, calcofluor)
• to visualize you need at least 106 organisms per mL (low sensitivity-negative doesnt mean negative)
– Then directly plated on agar media (4-quadrant streaking)
– Result is expressed as negative/rare/light/moderate/heavy depending on
how many quadrants show growth on agar plates
– Finalizing negative results takes 3-5 days
– General-purpose culture, may help to decide whether the isolated
organism is colonizing/contaminating only or significant enough to
implicate it as the cause of the inflammation
Examples: wound cultures, sputum cultures |
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Term
Microbiologic testing in clinical bacteriology practice
-Quantitative cultures |
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Definition
(colony-forming units (CFU) per volume)
– Specimen can be directly stained (Gram stain, AFB, calcofluor) as before
• to visualize you need at least 106 organisms per mL
– Specimen of known volume plated on agar media (lawn technique)
– Result is expressed as bacterial colonies (colony-forming units) per mL
– A predetermined CFU/mL cut-off can help to decide whether the isolated
organism is cause of the inflammation or not (UTI’s >105, ventilatorassociated
pneumonia >105)
Examples: urine cultures, bronchoscopic lavage cultures (BAL)In bronchiolavage specimen if i have more than 1000cfu/ml it might be cause of pneumonia, and if i don't it might be just colonizing not infections. skin biopsy cultures from burn patients |
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Term
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Definition
| Blood Urine, CSF, Feces,Sputum (material spat out from the lower airways) |
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Term
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Definition
Bacteremia or fungemia (infection of the bloodstream..shouldve been gone by spleen ) is a most serious infection and may be secondary to infections at other sites (for example, pyelonephritis or
pneumonia;causing endocarditis secondary to it). The blood should normally be sterile (free of circulating organisms)
Blood culture collection: The skin is cleaned and blood is collected and inserted into bottles containing liquid media (aerobe, anarobe.lm enables enhanced growth of bacteria/fungi). These
bottles contain resins to bind compounds inhibiting microbial growth.
•In order to increase the yield for Mycobacteria and some fungi, isolator blood cultures
are used. These are centrifuged at high speed, lysing immune cells containing
intracellular organisms, and then plated on media.
•Blood should be collected at two different sites at two different times. Since the skin is
covered by organisms, improperly collected blood cultures may be contaminated with
bacteria such as coagulase negative staphylococci or corynebacteria (diphtheroids)
1/2 sets positive, 2/2 sets positive |
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Term
| Other uses of blood (serum) for microbiologic diagnosis |
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Definition
Detection of fungal or parasitic proteins or antigens (Cryptococcus, Aspergillus,
malaria)
Direct microscopy to detect organisms (malaria, Babesia)
Detection of antibodies against bacteria, fungi, viruses or parasites by serology (eliza):
you do it again in two weeks IgM production which may not be apparent at the time of the patient presenting to physicians; a “convalescent” sample (collected 10-14 days after presentation) should be collected to detect late-occurring IgM and also changes in IgG titer. so do it twice.
Detection of viral RNA or DNA genomes by PCR (HIV, CMV) |
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Term
| How is HepA found using diagnostic tool |
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Definition
| 2-6 weeks after exposure, PCR can be done to the stool even before jaundice. At jaundice, IGM high.two weeks after, IgG higher and IgM lower. |
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Term
| Urine collection-The skin around penis and vagina may be contaminated with GI flora. How do you distinguish skin+bacteria collection from true positive? |
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Definition
–Presence of white blood cells (inflammation indicates infection)
–Absence of epithelial cells (presence indicates contamination from the meatus)
–More than 100,000 bacteria/mL urine (higher concentration of organisms make
an infection more likely than contamination)
–Only one kind of bacteria on urine culture (polymicrobial growth make
contamination from the meatus more likely than an infection |
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Term
| Urine can also be used for the detection of bacterial and fungal antigens such as? |
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Definition
| Legionella pneumophila and Histoplasma capsulatum and for viral genomes with PCR (BK virus in kidneytransplantation)Streptococcus pneumoniae for pneumonia |
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Term
| The CSF bathes the meninges and therefore, microbiologic examination of CSF may facilitate the diagnosis of?? |
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Definition
Meningitis. CSF can be tapped by a lumbar puncture and like
blood, CSF should be sterile. A cloudy appearance suggests the presence of leucocytes as an inflammatory response to bacterial infection (High protein and low glucose also..if you notice you start empirical treatment right away otherwise he dead)
A gram stain-bacterial infection;
An India ink dye-Cryptococcus neoformans (fungus) infection.
CSF can be cultured for bacteria, fungi and viruses.
PCR of CSF can detect viral gene targets (HSV). |
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Term
| Respiratory tract secretions |
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Definition
| •Sputum -spat out from the lower airways (not saliva). Since sputum has to pass through the pharynx and mouth there is potential for sputum to be contaminated with bacteria or fungi that are not truly causing disease so its tough one. Legionella Antigen detection, and SARS genome detection •A more invasive -obtain secretions directly from inflamed airspaces in the lung done by broncho-alveolar lavage (BAL). This makes oropharyngeal contamination by colonizing flora less likely. •Some diseases are best diagnosed by PCR and/or viral culture from nasopharyngeal swabs such as pertussis and influenza. |
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Term
| Aids in distinguishing true respiratory tract infection (pneumonia) from contamination? |
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Definition
| Presence of white blood cells (inflammation) Absence of epithelial cells (contamination) More than 10,000 bacteria/mL (BAL) One kind of bacteria on culture “Fitting” the disease |
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Term
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Definition
| Stool (feces) Microscopic examination can identify parasites infecting the gut, electron microscopy can identify some viruses but this is not often done in clinical practice. Culture can identify bacteria causing gastroenteritis; the use of selective media can differentiate normal gut flora from abnormal bacteria ( salmonella..you pour antibiotics to kill other bacteria so that you can concentrate) Toxins from some bacteria may also be found in the feces (Clostridium difficile) PCR can detect toxin genes of bacteria (C. difficile) and viruses (enterovirus) that normally do not colonize the gut. |
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