Microbiology and Pathogenesis Quiz

Host Pathogen Interactions Pt. II

• Host-pathogen interactions are critical in infectious disease establishment and progression
• Understanding these interactions is essential for physicians to effectively treat and prevent infectious diseases
• Stages of infectious disease are complex and vary depending on the stage of the disease

Why Do We Care? Host-Pathogen Interactions I

• The immune system fights pathogens, but pathogens can thwart the immune system
• This interaction fundamentally shapes the development and progression of an infectious disease; it plays a critical role.

Class Objectives

• Differentiate the 6 stages of infectious disease establishment and the 5 stages (periods) of infectious disease
• Define virulence factors and give examples
• Breakdown the role of transmission in establishing infection in a new host.
• Define the required nutritional elements for successful pathogen establishment
• Distinguish between obligate, facultative, and aerobe, anaerobe classifications relevant to pathogens
• Explain the significance of essential metal elements like iron to support pathogen growth
• Identify three types of bacterial toxins and provide examples of each.
• Compare and contrast antigenic drift and antigenic shift

Five Stages (Periods) of Infectious Disease

• Incubation: The time from infection to the appearance of symptoms
• Prodrome: Nonspecific symptoms like fever and fatigue herald the onset of specific disease symptoms
• Specific Disease Phase: Disease-specific symptoms occur
• Recovery (convalescence): Specific disease symptoms disappear.
• Health: Complete recovery; or becoming a chronic carrier, developing latent infection (e.g., herpes).

Virulence Factors

• Virulence factors enable pathogens to replicate and disseminate inside a host by subverting or eluding host defenses
• Adhesins: Surface proteins bind to host cells for attachment
• Capsules: Prevent phagocytosis
• Toxins (e.g., LPS): Harm host cells by various mechanisms
• Unique to particular strains: Specific toxins or factors

Goal: Survival

• Microbes have 3 key survival demands:
• Occupancy: Colonizing host cells
• Nutrition: Finding a suitable niche for survival
• Resistance: Surviving host defenses
• Transmission: Transferring to another host

Nutritionally Compatible Niche

• Bacteria have specific nutritional requirements, reflecting their ecological habitat
• The human body provides a suitable environment for microbial growth with diverse nutrients
• Oxygen requirements vary:
• Anaerobes: Thrive without oxygen
• Aerobes: Require oxygen
• Facultative anaerobes: Can grow in the presence or absence of oxygen
• Iron availability is a key factor for microbial growth and survival

Occupancy: Surface Colonization

• Bacterial adhesins (e.g., pili, surface proteins) mediate attachment to host cells and surfaces
• Some factors (e.g., capsules) prevent phagocytosis and enhance pathogen colonization.

Resistance: Surviving Host Defenses

• Microbes have evolved strategies to evade host defenses.
• Preventing the complement cascade, resisting phagocytosis, surviving inside phagocytes, establishing intracellular location, immune system suppression, resisting antibody proteolysis, latency, antigenic variation, and antigenic shift.

Becoming Intracellular

• Some microbes actively invade host cells to thrive and spread
• They often use host cytoskeletal systems for dissemination
• Example: Listeria monocytogenes

Immunosuppression

• Immunosuppression dampens host defense and allows microbes to replicate
• Damage to the immune system, inhibiting cytokine secretion, are relevant examples
• HIV

Diversion of Lymphocyte Function

• Superantigens are antigens that excessively activate T cells, leading to cytokine release.
• Non-specific activation of T cells and widespread cytokine release
• Example: Certain streptococci

Proteolysis of Antibodies

• Pathogens produce proteases that cleave antibodies, preventing the binding of other antibodies.
• These proteases are found in pathogenic bacteria

Latency

• Pathogens exist in a dormant state and are unaffected by the immune system; often long-lasting
• Viral examples include herpes and HIV. Bacterial examples include tuberculosis

Antigenic Variation

• Pathogens change their surface antigens to evade host immunity
• Examples include: Trypanosoma brucei, Neisseria gonorrhoeae, influenza viruses.

Test Your Knowledge #1

• Listing the strategies that pathogens use to avoid host defenses

Mechanisms That Damage the Host During Infection

• Pathological alterations of metabolism (toxins mimic hormones)
• Mechanical damage (obstruction or blockage of lymphatics)
• Damage caused by host response (e.g. cytokine storms, complement activation)

Mechanisms That Damage the Host During Infection-Cell Death

• Lysis: Disintegration of the cell
• Apoptosis: programmed cell death
• Part of normal cell cycle
• HIV & herpes: premature apoptosis
• Epstein-Barr virus blocks apoptosis, making cells immortal

Mechanisms That Damage the Host During Infection-Bacterial Toxins

• Intracellular: (various)
• Type III cytotoxins
• Type IV-VII cytotoxins
• Extracellular: (various)
• Endotoxins (LPS): Bacterial toxins.
• Membrane-damaging toxins
• Superantigens
• Extracellular matrix: (various)
• Exoenzymes: Bacterial enzymes that damage host tissue

Test Your Knowledge #2

• Questions relating to infection mechanisms

Test Your Knowledge #3

• Identifying the type of bacteria and rationale
• Obligate anaerobes cannot survive in oxygen
• Obligate aerobe needs oxygen
• Facultative aerobe can survive in or without oxygen

Also A Scientist

• Short biographical sketches from various microbiology scientists

General Principles of Laboratory Dx

• Methods of testing infection using various laboratory methods

Assessing the Performance of Diagnostic Tests

• Understanding sensitivity and specificity of lab tests
• True and false positives/negatives can influence how we interpret test results

Diagnostic Sensitivity and Specificity

• Sensitivity: Probability that the test will be positive in patients with the disease
• True Positives / (True Positives + False Negatives) x 100% = %
• Specificity: Probability that the test will be negative in patients without the disease
• True Negatives / (True Negatives + False Positives) x 100% = %

True vs. False

• Descriptions of true positives, true negatives, false positives, and false negatives.

Let's Apply It!

• Application of diagnostic concepts and calculation of sensitivity and specificity using a 2x2 table.

What is the Sensitivity? What is the Specificity?

• Numerical calculation for sensitivity and specificity based on supplied data
• Example interpretation

The Four Diagnostic Principles (Summarized)

• Microscopy: Examining samples for microbes.
• Culture: Growing and identifying microbes.
• Immune Response Measurement: Detecting pathogen-specific immune responses.
• Macromolecule Detection: Finding pathogen-specific molecules.

Diagnosing Infections by Microscopy: Stains

• Gram stains and acid-fast stains are used to identify bacteria based on their cell wall properties
• Useful where normally sterile body fluids are collected.
• Other stains (Giemsa, Lugol iodine, and Silver): Useful in identifying specific types of pathogens (protozoans, helminths, and fungi in various infections based on differential staining).

Diagnosing Infections by Microscopy: Antibody-Based Identification

• Specific antibodies are useful for enhancing the accuracy of microscopic identification.
• Monoclonal antibodies are more specific than polyclonal ones
• Methods like direct and indirect immunofluorescence use antibodies to detect antigens in samples

Diagnosing Infections by Culture(Summary)

• Culturing microbes involves growing them on selective media.
• Identification is then based on the phenotypic properties (e.g., colony morphology, growth rates).
• Antimicrobial sensitivity testing is used to assess how microbes respond to different antibiotic substances

Common Cultures: EMB & MacConkey Agar

• Specific media to indicate pathogen presence.
• Differential to distinguish different microbes via color/appearance change

Measuring the Antibody Response to Infection: Western Blot

• Used for measuring and evaluating the unique immune system response to infection.
• Separating antigens based on size using electrophoresis; transfer the separated bands onto a membrane; use antibodies to identify specific antigens.

Measuring the Antibody Response to Infection: ELISA

• A solid-phase assay is used to detect the presence and quantity of antibodies.
• A patient sample is combined with the specific antigen on a surface; unbound antibodies are then washed away, while enzymes and substrates are used to detect the antibodies bound to the antigen, which can be determined by the color change.

Test Your Knowledge #1

• Patient presentation case study; identify the most likely etiology based on symptoms and diagnostic tests

Diagnosing Infections by Detecting Pathogen Macromolecules

• Antigen detection tests to identify pathogen-specific antigens
• Nucleic acid-based diagnosis (e.g., PCR, microarrays, next-generation sequencing) to identify pathogen's DNA/RNA

Antigen Detection Tests (Summary)

• Simple serologic tests are used to capture and identify antigens.
• Methods like agglutination and ELISA are important examples of this technique

Nucleic Acid Amplification

• PCR is a method to amplify DNA/RNA sequences, making them easier to detect.
• Specific regions of microbial DNA/RNA are targeted.

Polymerase Chain Reaction (PCR)

• Amplifying specific DNA/RNA sequences for detection and analysis

PCR Debate

• Differences in usage of PCR in clinical vs. research settings

COVID-19 Testing Overview

• Different methods of COVID-19 testing and their pros/cons

Microarrays

• Identifying the presence of specific pathogens using DNA/RNA hybridization to detect multiple target sequences

Next-Generation Sequencing (NGS)

• Determining the complete genomic sequence for comprehensive information about a pathogen.
• To include determination of antibiotic resistance, virulence factors or typing.

Test Your Knowledge #3

• Interpreting results of a latex agglutination test

Also A Scientist

• Biographical information is provided

Prevention Strategies & Vaccines

• Prevention methods for infectious disease
• Importance of vaccination and its efficacy in preventing outbreaks, in addition to reducing associated morbidity and mortality

Three Categories of Travel Vaccines

• Routine, Required, and Elective vaccinations and their importance across different travel scenarios

History of Vaccination

• Historical overview of variolation and vaccination methods, showing the changing methods over time.

Variolation vs. Vaccination

• Variolation and vaccination methods comparing the two methods of prevention and disease risk.

How Vaccines Work

• Mechanisms of how various vaccine types function -Live-attenuated vaccines -Inactivated (killed) vaccines -Subunit, recombinant, polysaccharide and conjugate vaccines -DNA vaccines -RNA vaccines

Characteristics of Vaccines

• The criteria required for an effective vaccine

Why Boosters?!

• Explanations on why boosters are necessary/valuable and the rationale behind booster frequency given differing circumstances for the vaccine being administered.

What is an Adjuvant?

• The role of adjuvants in vaccines and examples

Did You Know...?

• A comparison of vaccine contents and naturally occurring levels of some chemicals.

What About Aborted Fetal Tissue?

• Examining the use of cell lines in producing and testing vaccines

Do Vaccines Cause Autism?

• A statement against the idea of autism being a cause resulting from vaccinations

COVID-19 is Affecting...

• Racial and ethnic disparities in COVID-19 outcomes
• Analyzing the distribution rates of infections
• Quantifying rates per region/race.

Racial Inequalities in Vaccination Rates

• Analysis of vaccine hesitancy and associated disparities in percentages per racial/ethnic groups.

Follow Up Resources

• Recommendations for additional reading or resources

Also A Scientist

• Biographical information on Kizzmekia S. Corbett

How Do We Address the Argument That Vaccines Aren't Tested Together?

• Testing methodologies for the simultaneous administration of multiple vaccines

BUT If I'm Healthy...Herd Immunity

• Describing the benefits of herd immunity

Breakthrough Strains

• Identifying different variants (by time period) along with their origin and spread rates.

How Do We Know if a Vaccine Is Effective?

• Interpreting numerical measures (e.g. VE) based on characteristics of individuals

The Biopharmaceutical Research and Development Process

• Outlining the time frame from the development of a new medicine to its approval to usage via step-by-step procedures involved from testing to approval

The Journey of Your Child's Vaccine

• Describing the development, approval, and manufacture of a new vaccine from the start
• Explaining various phases of testing

How a Vaccine Is Added to the U.S. Recommended Immunization Schedule

• Roles and importance of the Advisory Committee on Immunization Practices.
• Critical considerations in the development of recommendations for vaccines.

How a Vaccine's Safety Continues to Be Monitored

• Processes for monitoring the safety of vaccines once administered to the public
• Methods for collecting, analyzing, and responding to reports of adverse events following vaccination -Use of networks for healthcare information
• Reporting data from various sources.

Test Your Knowledge #2

• Patient case to which specific type of antibacterial agent would best treat the patient.