31 - Clinical Microbiology

Question 1

what is critical for the analysis of a specimen

Answer 1

quality; if not the results may be inaccurate or misleading; they will need to be recollected

Question 2

how long does it take for a culture

Answer 2

18-48 hours; sometimes longer

Question 3

what are the growth media types?

Answer 3

cell culture

artificial media - agar

Question 4

what is cell culture used for

Answer 4

a living system used for cultivating viruses and highly fastidious bacteria; observing for cytopathic effects

Question 5

what are the two forms of artificial culture media

Answer 5

liquid (broth)

Solid (agar)

Question 6

can you assess purity using liquid (broth) artificial culture media?

Answer 6

NO!

Question 7

can you use solid (agar) artificial culture media to assess purity

Answer 7

YES!

Question 8

what kind of system is artificial culture media

Answer 8

non-living system

Question 9

what can enriched media be used for?

Answer 9

nutritionally fastidious organisms

Question 10

2 organisms that can be seen using enriched media

Answer 10

Haemophilus and Neisseria

Question 11

what can we use when normal flora must be inhibited

Answer 11

selective media

Question 12

what selective agents can be put in selective media

Answer 12

dyes, antibiotics, salts

Question 13

what differential agents can be put into differential media

Answer 13

sugars (w/ pH indicator)

Question 14

what is differential media used for

Answer 14

to make certain organisms “look different” from others (colony appearance); useful when normal flora must be differentiated from potential pathogens

Question 15

what media is good for stool specimens

Answer 15

selective-differential media

Question 16

what will be critical factors for which media to select

Answer 16

disease
body site
suspected pathogens
presence/absence of normal flora

Question 17

what will be observed with macroscopic morphology

Answer 17

colony type (e.g. size shape, etc) heolysis (alpha, beta, gamma), pure vs mixed culture (visible difference of colonies)

Question 18

actinomyces macroscopic morphology

Answer 18

“molar tooth” colony

Question 19

Bacillus anthracis macroscopic morphology

Answer 19

“medusa head” colony

Question 20

Swarming proteus macroscopic morphology

Answer 20

waves of growth

Question 21

what does each type of hemolysis mean

Answer 21

alpha: partial hemolysis
Beta: complete hemolysis
Gamma: no hemolysis

Question 22

what does mixed culture often signify?

Answer 22

contamination with normal flora; generally limits ID/AST (antimicrobial susceptibility testing) of workup

Question 23

what are the different arrangements of microscopic morphology

Answer 23

clusters (staphlo-), chains (strepto-), pairs (diplo-), singly

Question 24

what is the turnaround time for biochemical tests?

Answer 24

few min - 24 hours

Question 25

what’s the turnaround time for molecular tests?

Answer 25

mass spectrometry: 10-30 min
sequencing: 24 hours

Question 26

examples of biochemical tests? what will be the product?

Answer 26

catalase (H2O2 to H2O & O2 -> bubbles)

glucose fermented to acid (decrease in pH - indicator turns color)

Question 27

what is the turnaround time, sensitivity, and specificity of Microscopy

Answer 27

15 min, low sensitivity, good specificity

Question 28

what is the turnaround time, sensitivity, and specificity of tests for antigen

Answer 28

15-30 min, low sensitivity, excellent specificity

Question 29

what is the turnaround time, sensitivity, and specificity of molecular tests

Answer 29

4-24hrs, excellent sensitivity and specificity

Question 30

steps of enzyme immunoassay

Answer 30

specific antibody bound to solid phase
add antigen solution; wash off unbound material
add specific antibody conjugated to enzyme; wash off unbound material
add substrate; color reaction if antigen present

Question 31

t/f you must know the target for primer in molecular amplification

Answer 31

true

Question 32

what will multiplex PCR panels detect

Answer 32

common causes of “syndromes” (fast, good sensitivity/specificity

Question 33

is serology a direct or indirect method?

Answer 33

indirect

Question 34

what will serology detect

Answer 34

specific antibodies to infectious agent

Question 35

what will > 4-fold rise in titer for serology mean

Answer 35

recent infection

Question 36

what will < 4-fold rise in titer for serology mean

Answer 36

past infection

Question 37

clinical indications of serology

Answer 37

retrospective diagnosis if acute and convalescent sera required
most accurate and rapid method if culture impossible and/or mere presence of antibody indicates infection
best indicator of immunity
best indicator of population exposure

Question 38

how can the presence of an antibody be interpreted with serology testing

Answer 38

patient was exposed to agent in the past
i might indicate that the pt is immune to infection or reinfection
it might suggest a diagnosis

Question 39

how can the absence of an antibody be interpreted with serology testing

Answer 39

the pt was not exposed to the agent or they were exposed w/n 7 days

Question 40

what are the different methods for antimicrobial susceptibility

Answer 40

culture based - phenotypic
molecular based - genotypic

Question 41

when is antimicrobial susceptibility testing (AST) performed

Answer 41

three overarching principles
1) isolate must be clinically significant (i.e. a potential pathogen)
2) antimicrobial susceptibility pattern of isolate is unpredictable
3) a standardized method is available for AST performance and interpretation on the isolate

Question 42

can you use AST (antimicrobial susceptibility testing) with a mix of different pathogens?

Answer 42

no, requires isolation of pathogen