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
