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Questions and Answers
What is lysis in the context of cell infection?
What is lysis in the context of cell infection?
Which of the following bacteria is associated with the production of toxins that damage cell membranes?
Which of the following bacteria is associated with the production of toxins that damage cell membranes?
Which mechanism can lead to programmed cell death?
Which mechanism can lead to programmed cell death?
Which type of toxin is specifically classified as an extracellular matrix target?
Which type of toxin is specifically classified as an extracellular matrix target?
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Which factor is likely responsible for promoting premature apoptosis in host cells?
Which factor is likely responsible for promoting premature apoptosis in host cells?
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In a case of bacterial infection, which mechanism is not a form of damage during infection?
In a case of bacterial infection, which mechanism is not a form of damage during infection?
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Which type of bacteria is most likely to quickly die off in the presence of oxygen?
Which type of bacteria is most likely to quickly die off in the presence of oxygen?
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What indicates a positive result in a simple agglutination assay?
What indicates a positive result in a simple agglutination assay?
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What occurs during the prozone phenomenon in an agglutination test?
What occurs during the prozone phenomenon in an agglutination test?
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In an ELISA, what happens if there is no antigen present in the sample?
In an ELISA, what happens if there is no antigen present in the sample?
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What is the first nucleic acid-based test that was developed?
What is the first nucleic acid-based test that was developed?
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What is required for hybridization in DNA probe testing?
What is required for hybridization in DNA probe testing?
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What does sensitivity measure in a diagnostic test?
What does sensitivity measure in a diagnostic test?
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Which of the following describes specificity in diagnostic testing?
Which of the following describes specificity in diagnostic testing?
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What outcome does a false negative indicate?
What outcome does a false negative indicate?
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How can the sensitivity and specificity of a test be quantified?
How can the sensitivity and specificity of a test be quantified?
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What is the primary purpose of conducting a microscopic examination of patient samples?
What is the primary purpose of conducting a microscopic examination of patient samples?
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Which of the following represents a true positive?
Which of the following represents a true positive?
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What does measurement of a pathogen-specific immune response in a patient indicate?
What does measurement of a pathogen-specific immune response in a patient indicate?
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If a diagnostic test has high specificity, what does it imply?
If a diagnostic test has high specificity, what does it imply?
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What information is typically represented in a 2 × 2 table used for diagnostic tests?
What information is typically represented in a 2 × 2 table used for diagnostic tests?
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What is the primary purpose of Gram stains and acid-fast stains in diagnosing infections?
What is the primary purpose of Gram stains and acid-fast stains in diagnosing infections?
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Which stain is primarily used to detect systemic protozoal infections?
Which stain is primarily used to detect systemic protozoal infections?
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What type of antibody is noted for being the most specific in enhancing microscopic identification?
What type of antibody is noted for being the most specific in enhancing microscopic identification?
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In which method do you add an unlabeled primary antibody followed by a secondary antibody for detection?
In which method do you add an unlabeled primary antibody followed by a secondary antibody for detection?
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What is a common characteristic of selective media used in microbial culture identification?
What is a common characteristic of selective media used in microbial culture identification?
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Which process directly inoculates blood into nutrient broth to check for microbial growth?
Which process directly inoculates blood into nutrient broth to check for microbial growth?
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What does antimicrobial sensitivity testing help determine?
What does antimicrobial sensitivity testing help determine?
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Which stain is utilized for detecting intestinal helminths?
Which stain is utilized for detecting intestinal helminths?
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What is the main use of serology in diagnosing infections?
What is the main use of serology in diagnosing infections?
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Which of the following is NOT used in the diagnosis of infections by microscopy?
Which of the following is NOT used in the diagnosis of infections by microscopy?
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What is the primary purpose of the Western blot technique in microbial diagnostics?
What is the primary purpose of the Western blot technique in microbial diagnostics?
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What role does the enzyme play in the ELISA test?
What role does the enzyme play in the ELISA test?
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Which type of agar is most suitable for culturing E. coli in the scenario described?
Which type of agar is most suitable for culturing E. coli in the scenario described?
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Which method enables the detection of pathogen macromolecules in a patient's sample?
Which method enables the detection of pathogen macromolecules in a patient's sample?
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What does the term 'solid-phase assay' refer to in the context of ELISA?
What does the term 'solid-phase assay' refer to in the context of ELISA?
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What characteristic makes Western blot one of the most specific serologic methods?
What characteristic makes Western blot one of the most specific serologic methods?
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In an ELISA, what happens to antibodies that do not bind to the antigens?
In an ELISA, what happens to antibodies that do not bind to the antigens?
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Which factor can a second antibody in an ELISA assay be designed to recognize?
Which factor can a second antibody in an ELISA assay be designed to recognize?
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What is a key advantage of using nucleic acid-based diagnosis of infection?
What is a key advantage of using nucleic acid-based diagnosis of infection?
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Which of the following techniques is synonymous with antigen detection tests?
Which of the following techniques is synonymous with antigen detection tests?
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Study Notes
Host Pathogen Interactions Pt. II
- Before learning about how the immune system fights pathogens, now will elaborate on what happens when pathogens thwart the immune system.
- Host-pathogen interactions are critical to the development of infectious disease.
- As a physician, understanding these complex interactions is vital for treatment and prevention based on the stage of infection.
WHY DO WE CARE? HOST-PATHOGEN INTERACTIONS I
- Bacteria enter bloodstream
- Immune system responds to fight infection
- Local infection caused by bacteria spreads throughout the body causing uncontrolled inflammation
- Leads to organ damage and death if left untreated
CLASS OBJECTIVES
- Differentiate between the 6 Stages of Establishment of Infectious Disease & 5 Stages (Periods) of Infectious Disease
- Define and give examples of virulence factors
- Further breakdown Reservoir Of Infection (RON) & learn about transmission to new hosts
- Define requirements for a nutritionally compatible niche (i.e. oxygen- aerobe v. anaerobe, facultative v. obligate; & iron)
- Identify mechanisms of cell death and how microorganisms perform them
- Identify the three types of bacterial toxins & give examples of each
- Compare & contrast antigenic drift & antigenic shift
FIVE STAGES (PERIODS) OF INFECTIOUS DISEASE
- Incubation: Time from acquisition to onset of symptoms.
- Prodrome: Nonspecific symptoms (fever, tiredness)
- Specific Disease: Disease-specific symptoms
- Recovery: Aka, convalescence.
- Health: May become chronic carrier or develop latent infection.
VIRULENCE FACTORS HELP ESTABLISH INFECTION/DISEASE
- Virulence factors enable pathogens to replicate and disseminate inside a host by subverting or evading host defenses.
- Adhesins: Surface proteins that bind to host cells
- Capsules: Inhibit phagocytosis
- Toxins: E.g., Lipopolysaccharide (LPS)
- Unique toxins: E.g., Botulinum toxin
- Other unique factors (example): Gp120 facilitates HIV entry into host cells
GOAL: SURVIVAL
- Three demands of free-living microbes:
- Avoid being washed away (colonize host cells, occupancy)
- Find a nutritionally compatible niche (nutrition)
- Survive innate and adaptive defenses (resistance)
- Transmit to a new host
NUTRITIONALLY COMPATIBLE NICHE
- Nutritional requirements often reflect ecological habitat.
- Will select environments that support their nutritional requirements.
- Ideal microenvironment for microbes: sugars, vitamins, minerals, etc.
- Oxygen: Aerobes, Anaerobes, Facultative, Obligate
- Iron: Bacteria need iron for synthesis of cytochromes & enzymes; Human body decreases free iron concentration in bacterial infection; Bacteria excrete siderophores to steal iron from host
OCCUPANCY- SURFACE COLONIZATION
- Adhesins: Cell-surface components of bacteria that facilitate adhesion
- Pili (fimbriae): Bind to special receptors.
- Invasin (Nonfimbrial surface protein): Binds to integrin
- Surface proteins: Bind to fibronectin
- Capsule: Composed of polysaccharides, principal antiphagocytic
- Rare exception of Gram+ bacteria having fimbriae, but know it's "unique" to Gram- bacteria for exam
Bacterial Colonization
- P pili & Type I pili, curli pili, type IV pili
- Spa, GAS M1, PI-1 & PI-2
- Curli pili, MSCRAMMs
- Adheres bacterial cells to each other and host structures
- Biofilm, Vegetation on AV valve
RESISTANCE- SURVIVING THE CONSTITUTIVE & INDUCED DEFENSES
- Mechanisms to evade host's first line defenses
- Defending against complement
- Subverting phagocytosis
- Surviving inside phagocytes
- Becoming intracellular
- Immunosuppression
- Diversion of Lymphocyte Function
- Proteolysis of Antibodies
- Latency
- Antigenic Variation (& Antigenic Drift & Shift)
I. DEFENDING AGAINST COMPLEMENT
- Complement: Circulating plasma proteins that recognize pathogens and become activated.
- Causes opsonization and killing of bacteria.
- Opsonization: Antibodies attached to pathogens to mark for destruction.
- Activation pathways: Classical, Alternative, and Mannose-Binding Lectin
- MAC (Membrane Attack Complex)
2. SUBVERTING PHAGOCYTOSIS
- Phagocytosis: Ingestion of bacteria or other materials by phagocytes.
- Avoid being phagocytized
- Killing phagocytes
- Avoiding neutrophil extracellular traps (NETs)
- Escaping ingestion/capsules
- Humiliation
- Paralyzes function
3. SURVIVING INSIDE PHAGOCYTES
- Inhibition of lysosome fusion with phagosomes
- Escape into the cytoplasm
- Resistance to lysosomal enzymes
- Inhibition of phagocytes oxidative pathways
- Murder, membrane lysis
- Indifference (resist lysosomal enzymes)
- Protection (surface lipophosphoglycan)
- Redirect phagosomal trafficking/Remove host proteins
4. BECOMING INTRACELLULAR
- Some cells thrive inside phagocytes
- Trigger infected cells to fuse with uninfected neighbors
- Spread into adjacent cells
- Example bacteria (intracellular): Listeria monocytogenes
5. IMMUNOSUPPRESSION
- Immunosuppression damages immune cells (like T cells) or inhibits cytokine secretion.
- Example: HIV
6. DIVERSION OF LYMPHOCYTE FUNCTION
- Diversion of lymphocyte function
- Superantigens (Type of antigen that results in excessive activation of immune system)
- Non-specific activation of T-cells and widespread cytokine release
- Example: Certain streptococci
7. PROTEOLYSIS OF ANTIBODIES
- Proteolysis of antibodies: Making proteases (proteins that break proteins) that cleave specific antibody (immunoglobulin A).
- Sometimes a piece of IgA remains which prevents other antibodies from binding
- Found in pathogenic bacteria
8. LATENCY
- Pathogen present in the body but exists in a resting state without producing itself.
- Not affected by immune system, long-lasting
- Can reactivate in times of stress or decreased immune function
- Example pathogens: Herpes virus, HIV, tuberculosis
9. ANTIGENIC VARIATION
- Changing surface antigen (example pathogens): Trypanosoma brucei
- Variable surface glycoprotein
- Hundreds of genes code for different antigens
- When antibodies are created, they switch to producing a different antigen
- Example pathogens: N. Gonorrhoeae, Influenza
- Hemagglutinin binds to cell surface receptors
- Neuraminidase (changes the receptors)
TEST YOUR KNOWLEDGE #1
- Methods that microbes use to evade the host's first line of defense
TEST YOUR KNOWLEDGE #2
- Mechanism that damages the host during infection (and why)
- Given the choices, none is not a mechanism of infection.
TEST YOUR KNOWLEDGE #3
- Obligate anaerobe is the most likely culprit
ALSO A SCIENTIST
- Abigail Salyers (information about degrees, publications, etc.)
- Jane Hinton (information about degrees, publications, etc.)
- Michel Yao (information about degrees, research, etc.)
General Principles of Laboratory Dx
- Four diagnostic principles
WHY DO WE CARE? GENERAL PRINCIPLES OF LABORATORY DIAGNOSTICS
- Rapid diagnostic tests (RDTs) provide convenient results immediately to the patient
CLASS OBJECTIVES
- Describe the four diagnostic principles of laboratory diagnostics
- Assess the performance of different diagnostic tests
- Understand tests and the meaning of results
- Diagnose infections by culture
- Describe molecular and genetic approaches to study bacteria
ASSESSING THE PERFORMANCE OF DIAGNOSTIC TESTS
- True positive, True negative, False Positive, False Negative
- Sensitivity & Specificity calculation
- Calculation for Positive Predictive Value and Negative Predictive Value
DIAGNOSTIC SENSITIVITY AND SPECIFICITY: HOW RELIABLE IS THE TEST?
- Interpretation and factors to consider
- 2x2 Table
- sensitivity, specificity formula
TRUE VS FALSE
- Define true positive, true negative, false positive, and false negative results
LET'S APPLY IT!
- Sensitivity and Specificity using a matrix
WHAT IS THE SENSITIVITY? WHAT IS THE SPECIFICITY?
- Calculation of sensitivity and specificity using a matrix
THE FOUR DIAGNOSTIC PRINCIPLES
- Microscopic
- Cultivation and identification of microorganisms from patient samples.
- Measurement of a pathogen-specific immune response in the patient
- Detection of pathogen-specific macromolecules in patient samples
I. DIAGNOSING INFECTIONS BY MICROSCOPY- STAINS
- Gram stains & acid-fast stains
- Useful to detect presence of bacteria in normally sterile fluids (CSF, blood, urine)
- Helps differentiate microorganisms and select appropriate antibiotics
- Giemsa stain for protozoal infections
- Lugol's iodine stains for intestinal helminths
- Silver stains for systemic fungal infections
1. DIAGNOSING INFECTIONS BY MICROSCOPY- ANTIBODY BASED IDENTIFICATION
- Specific antibodies enhance accuracy of microscopic identification
- Application of monoclonal antibodies for specific epitopes
- Polyclonal antibodies applicable to less specific targets
- Direct Immunofluorescence (Conjugated Fluorophore)
- Indirect Immunofluorescence (Unlabeled primary antibody)
1. DIAGNOSING INFECTIONS BY MICROSCOPY- ANTIBODY BASED IDENTIFICATION DIRECT & INDIRECT IMMUNO-FLUORESCENCE
- Direct Immunofluorescence (Conjugated Fluorophore Antibody)
- Indirect Immunofluorescence (Unlabeled primary antibody)
2. DIAGNOSING INFECTIONS BY CULTURE
- Agar-based media and in a broth medium
- Blood culture (Direct inoculation)
- Sub-cultured & transferred to plates for identification (lysis-centrifugation technique)
- Culture identification: phenotypic properties, motility, utilization of nutrient substrates, enzyme production
- Selective media to identify specific cultures
2. COMMON CULTURES: EMB & MACCONKEY AGAR
- Lactose (+/-), colonies of various bacteria (E. coli, Enterobacter aerogenes, Proteus vulgaris, Salmonella typhimurium, Staphylococcus aureus)
2. DIAGNOSING INFECTIONS BY CULTURE
- Antimicrobial sensitivity testing for susceptibility to antimicrobial agents
- Zone of inhibition around disk
3. MEASURING THE ANTIBODY RESPONSE TO INFECTION- WESTERN BLOT
- Serology, examines blood serum
- Western blot for specific serologic methods for pathogens
- Protein bands are transferred to membranes for detection
3. MEASURING THE ANTIBODY RESPONSE TO INFECTION- ELISA
- Enzyme-linked immunosorbent assay (ELISA)
- Solid-phase assay for pathogen or pathogen antigens
- Enzyme-labeled anti-antibodies bind to patient antibodies
TEST YOUR KNOWLEDGE #1
- Stool culture agar choice for suspecting E. coli infection
4. DIAGNOSING INFECTION BY DETECTING PATHOGEN MACROMOLECULES (& GENETIC TESTING)
- Methods such as antigen detection tests
- Nucleic acid-based diagnosis (e.g. PCR, Microarrays)
- Next-Generation Sequencing
A. ANTIGEN DETECTION TESTS
- Like reverse serologic tests
- Simple agglutination assay
- Positive: clumping; Negative: no clumping
A. ANTIGEN DETECTION TESTS- ELISA & EIA
- Enzyme-linked immunosorbent assay (ELISA)
- Enzyme immunoassays (EIA)
TEST YOUR KNOWLEDGE #2
- Antimicrobial susceptibility testing results
- Identifying most effective antibiotic based on results
B. NUCLEIC ACID-BASED DIAGNOSIS OF INFECTION
- DNA structure and function (separation and hybridization)
- DNA probe tests and in situ hybridization
C. NUCLEIC ACID AMPLIFICATION - PREMISE BEHIND PCR
- Principle behind Polymerase Chain Reaction (PCR)
- Steps of amplification and amplicon analysis
POLYMERASE CHAIN REACTION (PCR)
- Real-time PCR, quantitative PCR (qPCR)
- Targeting specific segments of DNA
PCR DEBATE
- Nuanced approach depending on the situation & context
COVID-19 TESTING OVERVIEW
- Method, sample types, timing, comparison between RT, PCR, Serology and Antigen tests.
C. MICROARRAYS
- Identifying bacteria based on conserved sequences
- Hybridization to microarrays
D. NEXT-GEN SEQUENCING
- Determining DNA sequence of a complete bacterial genome
- Gaining data regarding bacterial resistance, virulence, and typing
- Useful in outbreak investigation
TEST YOUR KNOWLEDGE #3
- Determining if latex agglutination tests are positive or negative
ALSO A SCIENTIST
- Jane Hinton bio information.
- Kizzmekia Corbett bio information.
PREVENTION STRATEGIES & VACCINES
- Vaccine strategies and benefits
- Top 10 medical cost of skin diseases
- How vaccines eradicated common diseases
- Survival of human populations by year
- How vaccines work
CLASS OBJECTIVES
- Defining vocabulary
- Comparing and contrasting infectious and communicable diseases
- Differentiating between endemic, epidemic, and pandemic
- Describing types of transmission
- Identifying standard precautions
- Defining sterilization, disinfection, and antisepsis
- Describing different levels of disinfection and appropriate usage
DEFINITIONS
- Antisepsis, disinfection, germicide, high-level disinfectant, intermediate level disinfectant, low-level disinfectant, sterilization
TYPES OF TRANSMISSION
- Abiotic environmental factors (Fomites, Soil, Water)
- Animal vectors (Arthropods)
- Human-to-Human (Vertical, Horizontal)
HOW TO PREVENT INFECTIONS: STANDARD CLINICAL PRECAUTIONS
- Hand hygiene
- PPE (Use Personal Protective Equipment)
- Respiratory hygiene & cough etiquette
- Patient placement
- Environmental hygiene
- Laundry handling
- Safe injection practices
- Sharps safety
GOOD HYGIENE: PRIMARY WAY TO PREVENT INFECTIOUS DISEASES
- Proper Handwashing Methods
SCIENCE WITH KENNEN: WEAR YOUR MASKS
- Public Service announcement
PATHOGEN ELIMINATION: ANTISEPTICS VS. DISINFECTANTS VS. STERILIZATION
- Defining disinfectants, antiseptics, and sterilization
ANTISEPSIS
- Chemicals used on living tissue
- Alcohols, iodophors, Chlorhexidine, Parachlorometaxylenol, Triclosan
DISINFECTION
- Chemical and/or physical agents destroying most microbial forms
- Low-level, intermediate-level, high-level disinfectants
STERILIZATION
- Destroying all microbial forms including spores, mycobacteria
- Steam under pressure, ethylene oxide gas, hydrogen peroxide
GERMICIDAL PROPERTIES OF DISINFECTANTS AND ANTISEPTIC AGENTS
- Comparing effectiveness of disinfectants and antiseptics against various microorganisms
WHY BOOSTERS?
- Reasons behind booster vaccine recommendations
HOW VACCINES WORK
- Explanation of the process of vaccine generation, including mechanisms
VACCINES CAN BE PREPARED FROM VARIOUS MATERIALS DERIVED FROM PATHOGENIC ORGANISMS
- DNA and RNA vaccines, their applications and benefits
CHARACTERISTICS OF VACCINES
- Criteria fulfilled for effective vaccine protection from infection
WHY VACCINES ARE IMPORTANT
- Prevention of disease, herd immunity
BREAKTHROUGH STRAINS
- Variants emerge
SO HOW DO WE KNOW IF A VACCINE IS EFFECTIVE?
- Factors influencing vaccine effectiveness: characteristics of receipient, similarity between vaccine and the circulating virus
WHAT IS AN ADJUVANT?
- Ingredient used in some vaccines to enhance immune response
- Examples: Pertussis component, aluminum salts
DID YOU KNOW...
- Comparison of aluminum content in different sources (breast milk, formula, vaccines)
WHAT ELSE IS IN VACCINES?
- Thimerosal (ethylmercury
- Removal in vaccines from 1999
- Formaldehyde; naturally occurring levels in pears, and low levels in vaccines.
WHAT ABOUT ABORTED FETAL TISSUE?
- Viruses use host cells for replication purposes
DO VACCINES CAUSE AUTISM?
- Scientific evidence refutes the link.
COVID-19 IS AFFECTING BLACK, INDIGENOUS, LATINX, AND OTHER PEOPLE OF COLOR THE MOST.
- COVID-19 Racial Data Tracker
RACIAL INEQUALITIES IN VACCINATION RATES
- Willingness to get vaccinated across racial and ethnic groups
- Vaccination rates compared to overall population
FOLLOW UP RESOURCES
- Websites and social media accounts for reliable vaccine information
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Description
Test your knowledge on the mechanisms of bacterial infection and their effects on host cells. This quiz covers concepts like lysis, toxin types, and programmed cell death. Understand how bacteria can damage cellular structures and influence apoptosis.
