Exam 1 Lecture 3 Flashcards by Aditi Iyer

Two steps to interrupt infection disease

Isolation and Identification

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First step of infection is to:

Colonize

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What happens after a pathogen colonizes a replicative niche?

Multiplies, and once a significant amount of multiplication occurs, this can cause an infection

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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

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Diacrisis

dia = through; krisis = a judgment

Synonym for diagnosis

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Diagnosis

the determination of the nature of a disease

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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.

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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.)

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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

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Etiological agent

viable microorganism, or its toxin, that may cause disease in humans

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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

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Sterile specimen example

urine (depending on how it is collected) AND blood (assuming that the patient is free of bloodborne pathogens like HIV)

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Non-sterile site with microbiota example

Colon

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Why is it important to identify specimens?

to develop accurate hypothesis

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Methods of examination

Bright field, dark field, and fluorescence microscopy

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2 types of fluorescence microscopy

direct and indirect, both using fluorophore

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3 types of cultures

nutrient, selective, indicator

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nutrient culture

grows just about everything, particularly designed to grow organisms that are fastidious

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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?

1. Gross phenotype 2. Biochemical characteristics 3. Antigenic structures 4. Toxin production 5. Nucleic acid sequences 6. 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

1. Discover problems not previously identifiable | 2. Speed, sensitivity, specificity

List 3 drawbacks of using sequencing

1. False-positive results due to contamination 2. Contamination obscuring diagnosis 3. Limited ability to assess properties of the pathogen

What are some molecular detection techniques?

1. PCR 2. Traditional PCR + Sanger sequencing (dye terminator sequencing) 3. Traditional PCR + melting curve analysis 4. Next Generation Sequencing

What are the requirements for sequencing platform?

1. Accuracy for identification (taxonomy) 2. Informative about phylogeny (study of evolution of the organism) 3. Accurate evolutionary clock