Exam 1 Lecture 3 Flashcards
Two steps to interrupt infection disease
Isolation and Identification
First step of infection is to:
Colonize
What happens after a pathogen colonizes a replicative niche?
Multiplies, and once a significant amount of multiplication occurs, this can cause an infection
How does the body respond to multiplication of a pathogen?
Immune response is initiated to cause fever, involving 3 cytokines: IL-1, IL-6, and TNF-alpha
Diacrisis
dia = through; krisis = a judgment
Synonym for diagnosis
Diagnosis
the determination of the nature of a disease
What is the first step to formulating a diagnosis?
History! It is important to ask plentiful and specific questions that can be used to formulate an accurate hypothesis.
Examples of questions to ask during a history
What is the problem? (chief complaint) What makes it worse? Did you travel? What do you eat? What are your personal habits? (etc.)
Once you have the patient’s history, what do you do with it?
- Form a hypothesis
- Perform physical exam
- Run some imaging/tests using information gathered
- Prepare treatment plan
- Repeat and refine hypothesis in between these steps as necessary
Etiological agent
viable microorganism, or its toxin, that may cause disease in humans
Why is identification of etiological agents important?
- determine nature of disease
- predict course and potential outcome(s)
- tailor therapy: apply specific interventions to a clearly defined problem
- exclude non-infectious causes of symptoms
Sterile specimen example
urine (depending on how it is collected) AND blood (assuming that the patient is free of bloodborne pathogens like HIV)
Non-sterile site with microbiota example
Colon
Why is it important to identify specimens?
to develop accurate hypothesis
Methods of examination
Bright field, dark field, and fluorescence microscopy
2 types of fluorescence microscopy
direct and indirect, both using fluorophore
3 types of cultures
nutrient, selective, indicator
nutrient culture
grows just about everything, particularly designed to grow organisms that are fastidious
selective culture
allows for the growth of certain pathogens; useful for sorting pathogen from normal microbiota
indicator
useful for revealing particular aspects of its physiology
Why is it important to know about incubation?
different pathogens have different requirements for optimal propagation
True or false: temperature and presence of oxygen are often signals to alter gene expression in pathogens
True (also presence of CO2!)
Conventional identification relies on:
9 log amplification; ability to isolate single cells to identify the pathogen correctly
Gross phenotype
look at colony phenotype on the plate
Why is important to identify biochemical characteristics in pathogens?
They are often virulence determinants
Catalase
produced by pathogens that can cleave hydrogen peroxide
–> specifically, catalase is used by pathogens that use O2 to respire
Urease
urea is cleaved to form NH3 and CO2 to act as a buffer in stomach acid
–> example: H. pylori releases NH3 to buffer gastric acidity and colonize the gastric mucosa
Coagulase
fibrinogen is cleaved to form a fibrin clot, preventing white blood cells from entering the colonization/infection site
- -> example: S. aureus uses the enzyme coagulase to create a fibrin coat, and avoid detection from the immune system
- blood clot = roadblock!
What is an example of an antigenic structure?
Streptococcal polysaccharide
What are 6 tools to identify microbes?
- Gross phenotype
- Biochemical characteristics
- Antigenic structures
- Toxin production
- Nucleic acid sequences
- Flow of information
What is serological detection?
The identification of host immunoglobulins (antibodies) that are specific to recognizing antigens from pathogens
How is the humoral immune response measured?
It is measured by titer (higher dilution capable of producing a positive test result)
True or False: At the acute disease stage, antibody titer is the lowest
False. Antibody titer increases early on during infection.
Distinguish between acute disease and convalescent disease
Serological detection of infection gives us information on whether the patient is currently or was recently infected (acute disease) OR if the patient is completely recovered (convalescent disease)
True or False: There is a 10-fold increase in titer in acute vs. convalescent disease.
False. There’s a 4-fold increase in titer from the acute disease stage to the convalescent disease stage.
We can also evaluate results from serological detection by looking at the ratio of ___/___. Higher ___ is an indicator of primary infection, while higher ___ is an indicator of secondary infection.
IgM/IgG
IgM
IgG
What are the various phases in the graph of the primary immune response?
Latent period, Log phase, Plateau phase, and Decline phase
True or False: A very robust IgG response is characteristic of a second infection by the same antigen.
True
Can a dead pathogen cause infectious disease?
No, it needs to be able to replicate…the dead pathogen is advantageous to the development of vaccines
What is molecular detection and what organisms is it used for?
- Molecular detection is using nucleic acids to identify infection
- It is used for organisms that are difficult or impossible to cultivate
What is an example of a pathogen that is difficult to cultivate?
Tuberculosis
What is an example of a pathogen that is impossible to cultivate?
Mycobacterium leprae
List 2 technological advantages of using sequencing
- Discover problems not previously identifiable
2. Speed, sensitivity, specificity
List 3 drawbacks of using sequencing
- False-positive results due to contamination
- Contamination obscuring diagnosis
- Limited ability to assess properties of the pathogen
What are some molecular detection techniques?
- PCR
- Traditional PCR + Sanger sequencing (dye terminator sequencing)
- Traditional PCR + melting curve analysis
- Next Generation Sequencing
What are the requirements for sequencing platform?
- Accuracy for identification (taxonomy)
- Informative about phylogeny (study of evolution of the organism)
- Accurate evolutionary clock
