Hunter: Bacterial Diagnosis Flashcards
What is the most common reason for failing to establish an etiologic diagnosis?
failure of proper specimen collection
What is the primary problem with diagnosing bacterial infection?
distinguishing resident or normal flora microbes from those causing infection
microbes are in sterile site that can be accessed directly (e.g., needle aspiration of deep skin abscess, or blood collection)
direct specimen
microbes are in sterile site but must be collected through a non-sterile site (e.g., voided urine sample)
indirect specimen
Microbes are in site contaminated with normal flora (e.g., throat or stool culture)
contaminated specimen
ex: fecal sample (tons of microorganisms in poop)
What is the most common tool for specimen collection? What does transport media do? Should the transport container be aerobic or anaerobic?
sterile swab; prevents drying out, maintains neutral pH, and minimizes growth of contaminant; container can be aerobic or anaerobic depending on the microbe of interest
light focused directly on specimen (most common)
brightfield microscopy
central light is blocked, peripheral light only collected as scatter from microbes
darkfield microscopy
**organism shows up against a black backfield
similar to darkfield, except microbes are labeled with dye that fluoresces when it interacts with light of an appropriate wavelength
fluorescence microscopy
Compare simple stains to differential stains to special stains
simple stains: use a single dye to visualize bacteria
differential stains: used to distinguish different bacterial groups (gram positive PURPLE vs gram negative RED)
special stains: used to detect bacterial structures (like capsule or flagella)
made from animal or plant products supplemented with a variety of nutrients (grow many microbes, but there is no “universal” culture medium)
nutrient media
**ex: sheep blood agar
used when specific pathogens are sought in sites with an extensive microbial flora. Usually chemical additives or antimicrobials that inhibit unwanted microbial growth
selective media
**ex: MacConkey agar or Eosin Methylene Blue agar
contain substances designed to demonstrate biochemical or other features of specific pathogens (i.e., pH indicators of fermentation of specific sugars, or red blood cells that can be hemolyzed)
indicator media
Strictly (blank) bacteria die in the presence of oxygen. Specialized culture conditions are required to grow these microbes
anaerobic
Cultures of aerobic bacteria are maintained in an incubator at (blank) degrees. Some bacteria grown in air require CO2. These are called (blank)
35-37 degrees C; capnophilic
This procedure allows selection of the most effective chemotherapeutic agent against a bacterial isolate
antimicrobial sensitivity testing
These tests are used to determine the MIC of an antibiotic
broth dilution tests
agar diffusion tests
What is an acid fast stain?
Same as a gram stain, but acid-fast organisms stain RED while other things stain BLUE
*Acid-fastness is a physical property of certain bacteria, specifically their resistance to decolorization by acids during staining procedures
What are some methods to test antibody response
ELISA
Western Blot
Immunofluorescence
Why can the Ab response be limited in its usefulness in diagnosis?
it can take several weeks to develop; also, Ab detection can be entirely unreliable in immunocompromised patients
RAPID antigen detection systems have been developed to detect antibody in minutes. Give an example.
rapid strep test
A + rapid strep test can be relied on. But, what must you do if you get a - result?
culture verification (throat culture)
**WAIT to prescribe penicillin b/c most pharyngitis is VIRAL
Nucleic acid analysis tests are divided into two types
non-amplified vs amplified
Non-amplified assays are based on hybridization of nucleic acids from pathogens to labeled (blank)
probes
