31 - Clinical Microbiology Flashcards
what is critical for the analysis of a specimen
quality; if not the results may be inaccurate or misleading; they will need to be recollected
how long does it take for a culture
18-48 hours; sometimes longer
what are the growth media types?
cell culture
artificial media - agar
what is cell culture used for
a living system used for cultivating viruses and highly fastidious bacteria; observing for cytopathic effects
what are the two forms of artificial culture media
liquid (broth)
Solid (agar)
can you assess purity using liquid (broth) artificial culture media?
NO!
can you use solid (agar) artificial culture media to assess purity
YES!
what kind of system is artificial culture media
non-living system
what can enriched media be used for?
nutritionally fastidious organisms
2 organisms that can be seen using enriched media
Haemophilus and Neisseria
what can we use when normal flora must be inhibited
selective media
what selective agents can be put in selective media
dyes, antibiotics, salts
what differential agents can be put into differential media
sugars (w/ pH indicator)
what is differential media used for
to make certain organisms “look different” from others (colony appearance); useful when normal flora must be differentiated from potential pathogens
what media is good for stool specimens
selective-differential media
what will be critical factors for which media to select
disease
body site
suspected pathogens
presence/absence of normal flora
what will be observed with macroscopic morphology
colony type (e.g. size shape, etc) heolysis (alpha, beta, gamma), pure vs mixed culture (visible difference of colonies)
actinomyces macroscopic morphology
“molar tooth” colony
Bacillus anthracis macroscopic morphology
“medusa head” colony
Swarming proteus macroscopic morphology
waves of growth
what does each type of hemolysis mean
alpha: partial hemolysis
Beta: complete hemolysis
Gamma: no hemolysis
what does mixed culture often signify?
contamination with normal flora; generally limits ID/AST (antimicrobial susceptibility testing) of workup
what are the different arrangements of microscopic morphology
clusters (staphlo-), chains (strepto-), pairs (diplo-), singly
what is the turnaround time for biochemical tests?
few min - 24 hours
what’s the turnaround time for molecular tests?
mass spectrometry: 10-30 min
sequencing: 24 hours
examples of biochemical tests? what will be the product?
catalase (H2O2 to H2O & O2 -> bubbles)
glucose fermented to acid (decrease in pH - indicator turns color)
what is the turnaround time, sensitivity, and specificity of Microscopy
15 min, low sensitivity, good specificity
what is the turnaround time, sensitivity, and specificity of tests for antigen
15-30 min, low sensitivity, excellent specificity
what is the turnaround time, sensitivity, and specificity of molecular tests
4-24hrs, excellent sensitivity and specificity
steps of enzyme immunoassay
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
t/f you must know the target for primer in molecular amplification
true
what will multiplex PCR panels detect
common causes of “syndromes” (fast, good sensitivity/specificity
is serology a direct or indirect method?
indirect
what will serology detect
specific antibodies to infectious agent
what will > 4-fold rise in titer for serology mean
recent infection
what will < 4-fold rise in titer for serology mean
past infection
clinical indications of serology
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
how can the presence of an antibody be interpreted with serology testing
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
how can the absence of an antibody be interpreted with serology testing
the pt was not exposed to the agent or they were exposed w/n 7 days
what are the different methods for antimicrobial susceptibility
culture based - phenotypic
molecular based - genotypic
when is antimicrobial susceptibility testing (AST) performed
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
can you use AST (antimicrobial susceptibility testing) with a mix of different pathogens?
no, requires isolation of pathogen
