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PATH 3100 Exam 4. Questions & answers
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PATH 3100 Exam 4. Questions & answers
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PATH 3100 Exam 4Mycology - ANS-the study of fungi responsible for disease in humans
Mycoses - ANS-infections caused by fungi; cutaneous, subcutaneous, systemic,
opportunistic
Fungus - ANS-nucleated, spore-bearing; cell walls of chitin or cellulose; reproduce
sexually or asexually; includes moulds and yeasts
Mould - ANS-fungus composed of filaments that generally form a colony that may be
filamentous, powdery, woolly, or smooth
Yeast - ANS-a unicellular budding fungus that usually produces a soft, pasty, smooth
colony; usually no filamentous growth can be observed macroscopically
Characteristics of Fungi - ANS-Fungi kingdom, eukaryotic, cell wall (no peptidoglycan,
lipopolysaccharides, teichoic acids, chlorophyll, but has peptidomannan, gluons, and
chitins), cytoplasmic membrane
Candida albicans - ANS-most common yeast isolated, oral flora of gastrointestinal,
urinary, and respiratory tracts, "opportunist" causes thrush, vaginitis, cutaneous,
systemic infections, immunocompromised patients are susceptible
Cryptococcus neoformans - ANS-yeast, not normal flora but found in environment;
associated with fowl excreta, meningitis especially in AIDS patients, produces a capsule
(India Ink Stain), detection of capsular polysaccharide antigen in CSF and serum
POWERPOINT FLASH CARDS - ANS-
Diagnosis - ANS-may be clinical based on symptoms and patient history, testing may
include stain, culture, histology, molecular diagnostics, serological assays that detect
fungal cell was components
Bacteremia - ANS-the presence of viable bacteria in the blood, can occur without
symptoms
Sepsis - ANS-the systemic inflammatory response to infection. Clinical syndrome that
complicates severe infection. Characterized by the cardinal signs of severe
,inflammation (vasodilation, leukocyte accumulation, increased microvascular
permeability) Can occur without a positive blood culture
Pathophysiology of bacteremia and fungemia - ANS-entry of organisms from focus of
infection into lymphatics then the blood, cytokine release results in clinical
manifestations of "sepsis", bacteria do not replicate in the intravascular space except in
the presence of vascular damage or devices, damaged heart valves, or unusual blood
flow
Symptoms of bacteremia are usually the symptoms of the focal process from which it
arises plus the nonspecific symptoms of infection. Patients with serious, overwhelming
disease have sepsis with any or all of hypotension, multiple organ system failure,
delirium or coma, and high mortality rate
Transient - ANS-lasts minutes to hours, associated with manipulation of
colonized/infected material: dental (up to 90%), gu procedures (up to 50%), gi
procedures (up to 50%)
may be initial manifestation of focal infection such as pneumonia (5-30%), osteomyelitis
(30-50%), meningitis (50-90%), arthritis (20-70%)
Intermittent - ANS-periodic seeding from un-drained or inadequately treated focus
(abscesses, UTI, pneumonia, etc)
Continuous - ANS-intravascular infection such as endocarditis, vascular access
infection, septic thrombophlebitis
Risk factors and prognosis - ANS-a number of factors have been studied to predict
positive blood cultures but none are adequate to clearly indicate when to draw cultures
risk factors for increased mortality when cultures are positive are more straightforward:
advanced age, hospital-acquired infection, hypothermia, hypotension, leukopenia,
multiple underlying disease processes
Diagnostic strategy for blood cultures - ANS-1. proper sterile technique vital to reduce
contamination. Critical that iodine/iodophor remain on site for 4-5 minutes
2. arterial blood no better than venous
3. blood cultures should NOT be obtained through IV catheters
4. a blood culture is defined as 1 venipuncture irrespective of the number of bottles
inoculated
5. blood cultures are adequate to detect >99% of bacteremias detached by a single
system approach
, 6. for intermittent bacteremia the highest yield from cultures occurs in the 2 hours
preceding clinical symptoms: draw cultures as quickly as possible after symptoms occur
7. uniformly positive blood cultures obtained at different points in time suggest
intravascular infection
8. pattern of collection: draw cultures before antibiotics. for most infections obtain 2
cultures one right after the other; for possible endocarditis draw 3 blood cultures
separated in time by at least 30 minutes. If all cultures are negative at 24 hours, it may
be reasonable to draw 2 additional cultures, but it is more likely that positive information
will be obtained from a different procedure (viral cultures, viral amplification, serologies,
different culture media, different culture site Ex. bone marrow)
Interpretation of positive cultures - ANS-1. contamination always a consideration
2. to consider an organism a "true positive" review: H&P, temperature, WBC, patient's
course before and since culture obtained, results of cultures at other sites, evidence of
infection at a site, the organism isolated, and the number of positive cultures
3. depending on the organism grown, the time to culture positively is helpful: true
positives usually are identified in the first 48 hours, contaminants in 4-7 days
4. The number of positive bottles per set is NOT helpful
5. Quantitation is generally NOT helpful
Critical Factors in the detection of bacteremia - ANS-1. volume of blood (20-30ml better)
2. ratio of blood to broth (dilution of blood helps)
3. medium - the ingredients to help organisms grow
4. atmosphere of incubation
5. agitation of bottles
6. temperature of incubation
7. anticoagulants
8. gelatin
9. inactivators of antibiotics
10. cell lysis
Examination methods - ANS-1. conventional broth with gram-stain and subculture
(includes Septi-Chek)
2. Semi-automated (infrared detection with BACTEC 660/730)
3. lysis centrifugation (for moulds)
4. Continuous monitoring blood culture systems: reduced hands on time with continuous
observation of cultures, earlier detection of positives, but at higher costs with limited
media configurations. Now state of the art for larger labs
5. multiple real-time PCR of positive blood cultures bottles for most common pathogens
and resistance markers
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