question
2 main approaches of lab diagnosis of ID
answer
1. bacteriological --> staining and culturing the organism
2. immunological (serologic) --> identify organism via detection of Ab against the organism in the pt's serum
2. immunological (serologic) --> identify organism via detection of Ab against the organism in the pt's serum
question
Which is NOT an approach to the bacteriologic lab work?
a. Observing
b. Maintaining
c. Obtaining
d. Identifying
a. Observing
b. Maintaining
c. Obtaining
d. Identifying
answer
b. Maintaining
question
In most cases of serologic testing, a ___________ rise in Ab titer between the acute and convalescent-phase serum samples is considered to be significant.
a. two-fold
b. four-fold
c. ten-fold
d. fifteen-fold
a. two-fold
b. four-fold
c. ten-fold
d. fifteen-fold
answer
b. four-fold
question
True/False: The microscopic appearance is sufficient to speciate an organism.
answer
False --> but it allows an educated guess to be made about the genus which guides empiric therapy (ex: gram pos vs neg coverage)
question
Detection of ___________ indicates a current infection.
a. IgM
b. IgG
c. IgA
d. IgE
a. IgM
b. IgG
c. IgA
d. IgE
answer
a. IgM
question
When obtaining a pure culture, you initially use __________ agar because it supports the growth of many bacteria and the type of hemolysis can be observed.
answer
blood
question
What should you be most aware of when using blood agar?
a. it may spread HIV and other viral growth
b. there may be contamination from normal flora
c. viruses will not grow on blood agar
d. it needs to be chilled to 32 degrees Fahrenheit to activate the blood agar's inhibitors
a. it may spread HIV and other viral growth
b. there may be contamination from normal flora
c. viruses will not grow on blood agar
d. it needs to be chilled to 32 degrees Fahrenheit to activate the blood agar's inhibitors
answer
c. viruses will not grow on blood agar
question
Why can't you use blood agar for viruses and obligate intracellular bacteria, such as Chlamydia and Rickettsia?
answer
Because RBCs (remember BLOOD AGAR) do not have a functioning nucleus and are incapable of supporting the growth of either viruses or obligate intracellular bacteria
question
Which type of obligate intracellular bacteria will NOT grow on blood agar?
a. Chlamydia and Rickettsia
b. Neisseria and Haemophilus
c. Legionella pneumophila
d. H. influenzae and Bordetella pertussis
a. Chlamydia and Rickettsia
b. Neisseria and Haemophilus
c. Legionella pneumophila
d. H. influenzae and Bordetella pertussis
answer
a. Chlamydia and Rickettsia
question
Why would blood agar need to be heated?
a. to allow for the media to set
b. to kill off any bacteria before you innoculate the agar to prevent contamination
c. to make chocolate agar
d. to inactive inhibitors of certain bacteria
e. C and D
f. A and B
a. to allow for the media to set
b. to kill off any bacteria before you innoculate the agar to prevent contamination
c. to make chocolate agar
d. to inactive inhibitors of certain bacteria
e. C and D
f. A and B
answer
e. C and D
(heating blood agar makes it turn a chocolate color)
(regular blood agar contains inhibitors for certain bacteria, such as Neisseria and Haemophilus, so you have to heat it in order to inactivate these inhibitors)
(heating blood agar makes it turn a chocolate color)
(regular blood agar contains inhibitors for certain bacteria, such as Neisseria and Haemophilus, so you have to heat it in order to inactivate these inhibitors)
question
The function of blood agar is to detect ______________.
answer
hemolysis
A: shows hemolysis
C: no hemolysis
A: shows hemolysis
C: no hemolysis
question
Bordet-Gengou (potato) agar detects what type of bacteria?
A. Legionella pneumophila
B. Bordetella pertussis
C. H. Influenzae
D. Neisseria meningitidis
A. Legionella pneumophila
B. Bordetella pertussis
C. H. Influenzae
D. Neisseria meningitidis
answer
B. Bordetella pertussis (Bordet for Bordetella)
question
Charcoal yeast extract agar contains increased concentrations of iron and cysteine to allow growth and it detects _______________ _____________.
answer
Legionella pneumophila
question
Chocolate agar w/ factors V and X detects ______________ ____________.
answer
Haemophilus influenzae
question
Egg yolk agar is used to detect which enzyme produced by Clostridium species?
A. Lecithinase
B. β-Lactamase
C. Catalase
D. Oxidase
A. Lecithinase
B. β-Lactamase
C. Catalase
D. Oxidase
answer
A. Lecithinase
question
Eosin Methylene Blue Agar selects against gram _________ bacteria and differentiates between ___________ fermenters and non-fermenters.
answer
positive
lactose
lactose
question
Lowenstein-Jensen agar selects against gram_________ bacteria in the respiratory tract flora and contains lipids for growth.
You can detect ________________ _______________ with this agar.
You can detect ________________ _______________ with this agar.
answer
positive
Mycobacterium tuberculosis
Mycobacterium tuberculosis
question
MacConkey agar selects against gram __________ bacteria and differentiates between _________ fermenters and nonfermenters.
answer
positive
lactose
lactose
question
Which of the following agars would you use to detect Diptheria?
a. Triple sugar iron
b. Thayer-Martin
c. Tellurite
d. Egg yolk
a. Triple sugar iron
b. Thayer-Martin
c. Tellurite
d. Egg yolk
answer
c. Tellurite
question
This is a chocolate agar designed to isolate Neisseria gonorrhoeae and N. meningitidis from nonsterile sites.
answer
Thayer-Martin
question
This medium contains three carbohydrates and differentiates bacteria on fermentation of glucose, sucrose, lactose.
answer
triple sugar iron
question
When would you most likely perform a blood culture?
answer
When you suspect sepsis, endocarditis, osteomyelitis, meningitis, or PNA.
question
Most frequently isolated gram-pos cocci from the blood
answer
S. aureus
S. pneumoniae
S. pneumoniae
question
Most frequently isolated gram-neg rods from the blood
answer
E.Coli
Klebsiella pneumoniae
Pseudomonas aeruginosa
Klebsiella pneumoniae
Pseudomonas aeruginosa
question
Throat cultures are used primarily to detect the presence of which type of bacteria (an important and TREATABLE cause of pharyngitis).
answer
Group A Beta-hemolytic strep --> use blood agar
(such as Strep pyogenes)
(such as Strep pyogenes)
question
Which procedure is typically NOT DONE on a throat swab?
answer
Gram staining
WHY?
Because is it literally impossible to tell the difference bt normal flora and S. pyogenes
WHY?
Because is it literally impossible to tell the difference bt normal flora and S. pyogenes
question
If you do find colonies of Beta-hemolytic strep on blood agar, you should add a __________ disk to determine whether the organism is likely GAS.
answer
bacitracin
question
Most frequent cause of CAP
answer
S. pneumoniae
question
Most common cause of HAP
answer
S. aureus and gram. neg rods
question
If TB is suspected, an _______ fast stain should be done immediately.
answer
acid
question
The most important causes of acute bacterial meningitis are three encapsulated organisms. What are they?
answer
N. meningitidis
S. pneumoniae
H. Influenzae
S. pneumoniae
H. Influenzae
question
What are two causes of subacute meningitis?
answer
TB and Cryptococcus
question
What are the most common bacterial pathogens causing diarrhea in the US?
answer
Shigella
Salmonella
Campylobacter
Salmonella
Campylobacter
question
Stool cultures are primarily useful when the complaint is __________ diarrhea.
answer
bloody (not watery)
question
A ______________ _______ stain of the stool that reveals many leukocytes indicates that an invasive organism rather than a toxigenic one is involved.
answer
methylene blue
question
Which selective media would you use for Salmonella and Shigella, both gram neg rods that do not ferment lactose?
answer
MacConkey or Eosin-Methylene Blue
--> since they do NOT ferment lactose they appear colorless while E.coli appears purple with a green sheen
--> since they do NOT ferment lactose they appear colorless while E.coli appears purple with a green sheen
question
You can further differentiate between Salmonella and Shigella (both non-lactose fermenting) by using which type of agar?
a. tellurite
b. bordet-gengou
c. thayer-martin
d. TSI
a. tellurite
b. bordet-gengou
c. thayer-martin
d. TSI
answer
d. TSI
(can also use an agglutination test ---> antisera directed against the cell wall O antigens)
(can also use an agglutination test ---> antisera directed against the cell wall O antigens)
question
Most common cause of UTI
answer
E. coli
question
True or false: urine is sterile in the bladder
answer
True: but it acquires organs of the normal flora as it passes through the distal portion of the urethra
question
This is considered one of the most important pathogens in the genital tract.
answer
N. gonnorrhoeae
question
What can be assayed in a counterimmunoelectrophoresis test?
a. positively charged antigens
b. antibodies
c. bacterial DNA
d. negatively charged antigens
a. positively charged antigens
b. antibodies
c. bacterial DNA
d. negatively charged antigens
answer
d. negatively charged antigens
(such as capsular polysaccharides)
(such as capsular polysaccharides)
question
True/False: T. pallidum (aka syphilis) can only be grown on laboratory media
answer
False: it actually does NOT grow on lab media
--> serological testing
--> serological testing
question
Three types of nucleic acid-based tests
answer
1. nucleic acid amplification tests
2. nucleic acid probes
3. neucleic acid sequence analysis
these are the gold standard for many infections
2. nucleic acid probes
3. neucleic acid sequence analysis
these are the gold standard for many infections
question
Which of the following is not a benefit of nucleic acid testing:
a. highly specific
b. quite sensitive
c. faster than culturing
d. cost-effective and inexpensive
a. highly specific
b. quite sensitive
c. faster than culturing
d. cost-effective and inexpensive
answer
d. cost-effective
question
If the venipuncture site is inadequately disinfected, blood cultures are most often contaminated with what?
answer
S. epidermidis
question
The main purpose of performing a throat culture is to detect the presence of which bacteria?
answer
S. pyogenes
question
A sputum culture will be REJECTED by the lab if:
a. it is streaked with blood
b. it contains IgA Ab
c. it contains more epithelial cells than neutrophils
d. it contains pus
e. it contains sulfur granules
a. it is streaked with blood
b. it contains IgA Ab
c. it contains more epithelial cells than neutrophils
d. it contains pus
e. it contains sulfur granules
answer
c. it contains more epithelial cells than neutrophils
(its probably saliva and not sputum)
(its probably saliva and not sputum)
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