Bacterial Diagnosis - Hunter Flashcards
how do you diagnose a bacterial disease?
exam patient
institute treatment for suspected disease
collect specimen
give to lab and tell them what you think it is
lab will give results
physician implements appropriate therapy
What is the most common reason for failing to establish an etiologic diagnosis?
failure of proper specimen collection
confirmation of the clinical diagnosis of a bacterial infection requires collection of an (blank)
appropriate specimen
For bacteria infections, the primary problem is in distinguishing what?
resident/normal flora microbes from those causing infection
What is a direct specimen?
microbes are in sterile site that can be accessed directly (i.e needle aspiration of deep abscess or blood collection)
What is an indirect specimen?
microbes are in sterile site but must be collected through a non-sterile site (i.e. voided urine sample)
What is a contaminated specimen?
microbes that are in site contaminated with normal flora (i.e throat or stool culture)
T or F
The specimen and your presumptive diagnosis dictates how the clinical microbiology lab approaches the isolation and identification of the bacterial pathogen.
T
What is the most commonly used tool for specimen collection? What are its pitfalls?
sterile swab
only collects a small amount of sample and easily dries out
What is transport media for?
prevent drying out, maintain neutral pH and minimize growth of contaminants
Transport containers can be (blank) or (blank) depending on the particular microbe of interest.
aerobic
anaerobic
What are the ways to identify specific microbes in the clinical microbiology lab?
microscopy broth and agar culture (antibiotic sensitivity testing) biochemical characterization antibody detection antigen detection nucleic acid-based tests
What are the three microscopes used for direct examination of the specimen?
brightfield microscopy
darkfield micrscopy
fluorescence microscopy
What microscope is this:
light focused directly on specimen (most common)
brightfield microscopy
What microscope is this:
central light is blocked, peripheral light only collected as scatter from microbes
darkfield microscopy
What micrscope is this:
similar to darkfield, except microbes are labeled with dye that fluoresces when it interacts with light of an appropriate wavelength
fluorescence microscopy
Most bacteria are examined with a (blank) objection
100x oil immersion
What are the three kinds of stains for identifying bacteria?
simple stains
differential stains
special stains
What stain is this:
use a single dye to visualize bacteria
simple stains
What stain is this:
used to distinguish different bacterial groups (i.e gram positive vs. gram negative)
differential stains
What stain is this:
used to detect bacterial structures
(i.e capsules, flagella, and endospores)
special stains
What are the two most common bacterial stains?
gram stain and acid fast stain
Culture of microbes in (blank) or on (blank) medium is commonly used.
nutrient broth
agar
T or F
a single microbe can grow to amounts that are visible (i.e turbidity in broth or colonies on agar)
T
T or F
Almost all medically important microbes can be cultured
T
What are the four forms of bacteria colonies on agar?
circular, irregular, filamentous, rhizoid
What are the five elevations of bacterial colonies on agar?
raised, convex, flat, umbonate, crateriform
What are the five margins of bacterial colonies on agar?
entire, undulate, filiform, curled, lobate
What is this:
made from animal or plant products supplemented with a variety of nutrients (grow many microbes, but there is no ‘universal’ culture medium
nutrient media
What is this:
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
What is this:
contain substances designed to demonstrate biochemical or other features of specific pathogens (pH indicators of fermentation of specific sugars, or red blood cells that can be hemolyzed)
indicator media
Cultures of most (blank) are maintained in an incubator at 35 to 37 degrees celcius.
aerobic
Some aerobic bacteria are gorwn in air but require (blank)
CO2 (capnophilic)
Strictly (blank) die in the presence of oxyygen. What do you need for these bacteria to grow?
anaerobic
specialized cultures
What do you need to match to the microbes expected from the clinical examine and specimen collected?
Combos of broth, solid media, aerobic, CO2, anearobic incubation
What does antimicrobial sensitivity testing allow for?
allows selection of most effective chemotherapeutic agent against the bacterial isolate
How do you find the minimum inhibitory concentration of an antibiotic?
broth dilution tests and agar diffusion tests
The (blank) method has been fully automated in the clinical microbiology lab.
broth dilution
What do you use bacitracin (A) disk for?
for presumptive identification of strep pyogenes, which is sensitive to low concentration of bacitracin
What do you use bile solubility for?
for rapid differentiation of pneumococci (which are bile soluble) from other streptococci
What do you use catalase for?
an important characteristic that defines significant major groups of bacteria, (e.g. staphylococci {catalase positive} streptococci and enterococci {catalase negative}
What do you use coagulase for?
for identification of staphylococcus aureus
What do you use hippurate hydrolysis for?
a positive test is used for presumptive identification of group B strep. Indole A rapid test is used for presumptive identification of E. coli from urine specimens
What do you use Optochin (P) disk for?
suscpetibility to optochin is presumptive identification of strep pneumonia
What do you use oxidase for?
to help differentiate gram-negative rods
What do you use PYR hydrolysis for?
A rapid test for presumptive identification of S. pyogenes and enterococcus
How can you biochemically characterize pathogens?
via API20e System
Antibodies formed in response to most bacterial infections can be detected by methods such as (blank X 3)
ELISA, western blot, immunofluorescense
(blank) can indicate current, recent, or past infection
antibodies
What the downside of using antibodies to detect pathogens?
some antibodies to some becateria take several weeks to respond.
(blank) is quite useful in epidemiologic studies
serology
(blank) can be unreliabe in immunocompromised patients.
antibody detection
Whole bacteria, bacterial antigens, and bacterial toxins released into body fluids can be detected by (blank) using a variety of assays (e.g., immuno-fluorescence and ELISA)
antibodies
T or F
rapid antigen detection systems have been developed (e.g. rapid strep test)
T
What are the 2 types of assays in nucleic acid analysis?
non-amplified
amplified assays
How does non-amplified nucleic acid analysis work?
they are based on hybridization of nucleic acids from pathogens to labeled probes.
When do you want to use non-amplified assays?
to identify cultured bacteria where sensitivity is not as important
PCR based tests are the (Bank) and are the most commonly used in the diagnostic laboratory
amplified assays
When do you use PCR based test?
for sensitivity, they are extremely sensitive but subject to contamination. great care is needed to run good PCR tests
(blank) probes can be used to identify bacteria in clinical specimens
nucleic acid
The (blank) of most bacterial pathogens are known
genomes
(blank) can be designed to hybridize with specific DNA sequences
Probes
What assays are particularly useful when sensitivity is not an issue?
nucleic acid probes
