Bacterial Diagnosis - Hunter Flashcards
T/F: a physician should begin treatment when an infectious disease is suspected BEFORE lab confirmation
yes
What is the most common reason to fail to establish an etiologic diagnosis or a wrong diagnosis of an infectious organism?
Failure to properly collect a specimen
In diagnosing a bacterial infection, what is the primary problem?
distinguishing normal flora from those causing infection
What is a direct specimen?
microbes are in sterile site that can be accessed directly (e.g., 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 (e.g., voided urine sample)
What is a contaminated specimen?
Microbes are in site contaminated with normal flora (e.g., throat or stool culture)
what two factors will dictate how the micro lab will approach isolating and identifying the bacteria?
the type of specimen you collected and your presumptive diagnosis
T/F: transport of bacterial specimens is aerobic only
false, it can be either
Microscopy Broth and Agar Culture (antibiotic sensitivity testing) Biochemical Characterization Antibody Detection Antigen Detection Nucleic Acid-Based Tests
These are all methods of what?
identifying specific microbes in the lab
What type of microscopy focuses directly on the specimen?
brightfield
What type of microscopy has the central light blocked and peripeheral light is collected as scatter from the microbes?
darkfield
What type of microscopy has microbes labeled with fluorescent dye that interacts at a certain wavelength?
fluorescence
What type of microscopy is most common?
brightfield
What power mag do you need to see bacteria?
100x under oil immersion
What is the point of simple staining?
to just visualize bacteria
what is the point of differential staining?
to distinguish different groups of bacteria, such as gram pos/neg
what are special stains used for?
detect bacterial structures such as capsules, flagella, and endospores
what are the two most common stains?
Gram stain and acid fast
what medium is commonly used to grow bacteria?
agar
T/F: a single microbes can grow to visible amounts
true
T/F: almost all medically important microbes can be cultured
true
How do you describe the colony form?
Circular
irregular
filamentous
rhizoid
how do you describe colony elevation?
raised convex flat umbonate cateriform
how do you describe colony margins
entire undulate filiform curled lobate
What is the difference between nutrient, selective, and indicator media?
nutrient used to grow microbes, selective include antimicrobials to limit overgrowth of undesired bacteria, and indicator media has stuff that demonstrates specific activities of certain bacteria
what type of media should you use if you have a sample of intestinal flora?
selective media to limit floral overgrowth to SELECT for you bacteria
media that has a pH indicator of fermentation of sugars or RBC hemolysis is what type of media?
indicator media
MacConkey agar is what type of media and is used to grow what?
Selective and indicator, gram negative, shows lactose fermentation
Eosin Methylene blue agar is what type of media and is used to grow what?
Selective and indicator, gram negative, also shows lactose fermentation
Hektoen Enteric agar is what type of media and is used to grow what?
Selective and indicator, SPECIFICALLY salmonella and Shigella, shows lactose fermentation and HYDROGEN SULFIDE production
what does capnophilic mean?
bacteria grows in air but requires CO2
Strictly (blank) bacteria die in the presence of air
anaerobic
What are the factors that must be accounted for to grow bacteria? (3)
- Broth/solid media
- aerobic vs. anaerobic
- CO2 levels
What allows the selection of most effective chemotherapeutic agent against the bacterial isolate?
Antimicrobial sensitivity testing
What is used to determine the minimum inhibitory concentration (MIC) of an abx?
broth dilutions and agar diffusion
Bacitracin A disk is used to ID what bacteria?
Strep pyogenes
Bile solubility allow for rapid differentiation of (blank) from other streptococci
pneumococci
Catalase activity differentiates what two major groups?
staph (catalase pos) from strep and enterococci (catalase neg)
Coagulase positive is KEY for what bacteria?
staph aureus
Hippurate hydrolysis will ID group (blank) streptococci
group B
An (blank) rapid test will detect E. coli in the urine
Indole A (hippurate hydrolysis)
Optochin (P) disk can be used to ID what?
strep PNEUMONIAE; P for P
Oxidase activity differentiates what type of rods?
gram negative rods from each other
Enterobacteriaceae, Acinetobacter, and Stenotrophomonas are oxidase pos/neg?
oxidase negative
Pseudomonas and Burkholderia are oxidase pos/neg?
oxidase positive
S. pyogenes and Enterococcus can be determined via rapid test using what?
PYR hydrolysis
What detection lab methods do you use to visualize sera Abs?
ELISA, westerns, or immunofluorescence
The Ab response to some bacteria can take (days/weeks)?
weeks
Serology is mostly useful in what type of studies?
epidemiologic
T/F: Abs are a good detection mechanism of bacterial infection in immunocompromised patients?
FALSE
Can Abs detect whole bacteria or bacterial toxins?
yes
How does a non-amplified nucleic acid assay work?
hybridization of nucleic acids FROM pathogens TO labeled probes
Are rapid non-amplified nucleic acid tests sensitive?
NO; but they are fast
what is the amplifed NA test?
PCR
IS PCR sensitive?
extremely
T/F: the genomes of most bacterial pathogens are known
ture
When would sensitivity not be an issue when IDing bacteria?
after the bacteria has bee grown up in vitro so you have a lot of it vs. trying to test in vivo
