Lecture 2 9/1/23 Flashcards
How can infecting agents be detected?
-microscopic examination
-isolation and ID
-antigen and toxin detection
-nucleic acid detection
How can host immune response be detected?
-detecting antibodies
-detecting cellular response (IFN-gamma, PPD skin test)
When can the infectious agent be detected?
-entry of pathogen
-dissemination of pathogen
-colonization and disease
When can antibodies be detected?
-colonization and disease
-pathogen elimination
What are the characteristics of microscopic pathogen detection?
-cost effective
-provides info. on number and morphologic characteristics
-provides info. on likelihood of infection, likely pathogens, predominant organisms
What are the downfalls of microscopic pathogen detection?
-low sensitivity
-low specificity
-some bacteria do not stain
Why do gram neg. bacteria show up pink?
-thin peptidoglycan allows for primary stain to be washed out
-counterstain is picked up
Why do gram pos. bacteria show up purple?
-thick peptidoglycan holds the primary stain in
-counterstain color does not dominate primary stain
Why do acid fast pos. bacteria stain pink?
presence of mycolic acid holds onto the primary stain
Why do acid fast neg. bacteria stain blue?
absence of mycolic acid prevents primary stain from sticking
What are the routine culture procedures?
-aerobic culture
-anaerobic culture
-microaerophilic culture
-fungal culture
Why are special culture procedures valuable?
they provide very specific results regarding individual pathogens
Why is timing an important factor when deciding whether or not to culture?
not all pathogens multiply fast enough to provide culture results in a timely manner
Which bacteria cannot be cultured on lab media?
obligatory intracellular bacteria
Which bacteria types require oxygen for growth?
-aerobic
-microaerophilic
-capnophilic
Which bacteria types do not require oxygen for growth?
-obligate anaerobic
-aerotolerant anaerobic
Which bacteria types can utilize oxygen if present?
facultative anaerobic
How are biochemical tests used to identify bacteria?
-each test provides information about a bacteria’s properties
-unique combinations of each test result can help to identify bacteria
What is polymerase chain reaction?
the amplification and detection of DNA
What reaction components are needed for conventional PCR?
-primers
-deoxynucleotide phosphates
-enzymes
-template DNA
What additional reaction component is needed for real-time PCR?
labelled probes/fluorescent dyes
What are antigen detection tests?
tests that utilize specific antibody reagents to detect pathogens in clinical samples
What is seroconversion?
antibody development after exposure to a pathogen/antigen
How are antibody responses detected?
using body fluids, typically serum
How are cell-mediated responses detected?
using immune cells or body’s reaction to pathogen components
What is an antibody titer?
measurement of serum antibody level against an infectious agent
How are antibody titers expressed?
reciprocal of the highest dilution of serum that positively reacts in specific test
What are paired titers?
-titers determined at 2-4 week interval during course of infection
-four fold increase between titers suggests active infection
What is the relationship between titer reading and titer level?
the higher the titer reading, the more antibodies present
How does BSL level correlate with risk and practices?
-the higher the BSL level, the greater risk to humans
-the higher the BSL level and risk, the greater precautions that must be taken (better/more equipment, etc)
