Ch. 14+15 - Principles of Disease and Epidemiology _ Microbial Mechanisms of Pathogenicity

CONCEPT: SYMBIOTIC RELATIONSHIPS

  • Interaction between different living organisms, such as humans and microorganisms, can form different types of relationships.

  • Symbiosis: It refers to biological interactions or relationships between two organisms/species.

  • There are three forms of symbiotic relationships:
    1) Mutualism: Relationship where both organisms benefit from the interaction.
    2) Commensalism: Relationship where one organism benefits while the other is not affected.
    3) Parasitism: Relationship where one organism benefits at the expense of the other, causing harm to the other organism.

  • All pathogens are categorized as parasites.

PRACTICE QUESTIONS

  • Practice Question: Organisms that interact and live together on a permanent basis are termed:

    • a) Mutualism

    • b) Parasitism

    • c) Symbiosis

    • d) Transient microbiota

  • Practice Question: A relationship where one partner benefits and the other is harmed is termed:

    • a) Commensalism

    • b) Parasitism

    • c) Independence

    • d) Mutualism

CONCEPT: THE HUMAN MICROBIOME

  • Microbiome (or Normal Flora): Refers to communities of microbes that inhabit and grow on/in the bodies of all humans.

  • These microbes live in symbiotic relationships with humans and can be classified into two groups:
    1) Resident Microbiota: These are microbes that are almost permanently present on the host for extended periods of time.
    2) Transient Microbiota: These are microbes that are only temporarily found in the body. (E.g., pathogens)

PRACTICE QUESTIONS

  • Practice Question: The description of humans as "superorganisms" refers to:

    • a) Humans being the most intelligent organisms.

    • b) Each human being an ecosystem for trillions of microorganisms.

    • c) Humans determining the success of other organisms.

    • d) Each human being host to unique species of microorganisms.

  • Practice Question: Which of the following does not include an example of transient microbiota?

    • a) Microorganisms that inhabit certain body sites for extended periods of time.

    • b) Microorganisms that can inhabit different body sites during their lifetime.

    • c) Microorganisms that occupy the body for a short period of time.

    • d) Microorganisms that are pathogenic and removed by the body’s immune system.

CONCEPT: MICROBIOME COMPOSITION

  • The Human Microbiome Project (initiated in 2007) studies the relationships of normal flora with various human hosts.

  • Goal: Understand how changes in a microbiome affect human health and disease.

  • Humans begin developing their microbiomes at birth, with breast milk providing many beneficial microbes and carbohydrates essential for an established microbiome.

  • In adults, numerous factors influence changes in microbiomes, such as obesity, which results in different microbiome compositions compared to lean adults.

  • Over time, an individual’s microbiome can change as they encounter new microbes.

  • Research correlates microbiome compositions with various health outcomes, for instance, intestinal dysbiosis could lead to inflammatory bowel disease.

PRACTICE QUESTIONS

  • Practice Question: Factors influencing types and amounts of microorganisms on/in the body include:

    • a) Age

    • b) Diet

    • c) Medications

    • d) All of the above

  • Practice Question: Babies born via cesarean section may have a higher risk of developing allergies due to:

    • a) Lack of exposure to mother’s vaginal microbiota.

    • b) Early exposure allowing quicker microbiome formation.

    • c) Less developed microbiome leading to increased sensitivity to allergens.

    • d) All of the above.

CONCEPT: HOST INTERACTIONS WITH MICROBIOTA

  • Newborns acquire microbiota from various sources:

    • a) Passing through the birth canal

    • b) Breastfeeding

    • c) Contact with mother’s skin

    • d) Their environment

    • e) All of the above are sources of microbiota.

MICROBIOME PROTECTION AGAINST INFECTIONS

  • The microbiome contributes to innate immunity by creating a competitive and unfavorable environment for pathogens.

  • Some microbes occupy the attachment sites of pathogens, preventing their colonization and growth.

  • Other microbes synthesize substances that can be harmful to pathogenic microbes.

  • The microbiome can also boost the adaptive immune system's response. For instance, if small numbers of skin microbiota enter tissues, the body produces antibodies against them, which can be effective against pathogens with similar antigens.

PRACTICE QUESTIONS

  • Practice Question: Identify effective ways the microbiome helps protect the body from pathogens:

    • a) Creates compounds to assist in digestion.

    • b) Produces harmful substances for pathogens.

    • c) Competes for resources with pathogenic microbes.

    • d) Blocks entrances/binding sites in the body.

    • e) All choices are true.

  • Practice Question: Understanding the link between Lactobacillus species and yeast infections:

    • a) The yeast is a pathogenic microbe in the vagina.

    • b) Lactobacillus and yeast compete for resources in a healthy microbiome.

    • c) Antibiotics cause an imbalance in vaginal bacterial and yeast populations.

CONCEPT: IMMUNE TOLERANCE

  • T & B Cells: Must build immune tolerance to microbiota to prevent autoimmunity.

  • Immune Tolerance: The ability for the immune system to differentiate between harmless substances (like microbiota) and harmful pathogens.

  • TReg cells prevent the activity of other T cells to avoid targeting host microbiota and self-cells.

  • Studies suggest that early and sufficient exposure to microbes in childhood enhances Treg cell activity.

HYGIENE HYPOTHESIS

  • The hygiene hypothesis posits that insufficient microbial exposure increases the risk of allergies and autoimmune disorders due to lack of immune tolerance development.

PRACTICE QUESTIONS

  • Practice Question: The hygiene hypothesis suggests that:

    • a) Lack of microbial exposure may promote allergies.

    • b) Hand washing prevents dangerous infections.

    • c) Immune systems function best in clean environments.

CONCEPT: NUTRIENT PRODUCTION AND DIGESTION

  • The microbiome assists in producing essential nutrients for the host.
    1) Vitamins B & K: Synthesized by the intestinal microbiome and absorbed by the host.
    2) Complex Carbohydrates: Degraded by the intestinal microbiome to support host digestion.
    3) Short-Chain Fatty Acids: Produced via fermentation by bacteria, serving as energy for epithelial cells in the gut.

PRACTICE QUESTIONS

  • Practice Question: How do gut microbiota help digest dietary fibers?

    • a) By digesting the fiber directly.

    • b) By creating vitamins that assist in breaking down fiber.

    • c) By inducing intestinal cells to create the degrading enzymes.

CONCEPT: CHARACTERISTICS OF INFECTIOUS DISEASE

  • Infection: Refers to the colonization and replication of pathogens in a host.

  • Infectious Disease: Spreadable diseases resulting from infections, identified by observable signs and symptoms.

    • Signs: Objective evidence observable by others (e.g., rashes).

    • Symptoms: Subjective evidence that cannot be directly observed (e.g., pain).

  • Asymptomatic Disease: Infections present without observable signs or symptoms.

COMMUNICABLE VS. NONCOMMUNICABLE DISEASES

  • Communicable Diseases: Infectious diseases that can spread from host to host.

  • Infectious Dose: The minimum number of microbes needed to establish an infection.

  • Noncommunicable Diseases: Non-infectious diseases that do not spread between hosts (e.g., cancer), arising from various factors like genetics and lifestyle.

PRACTICE QUESTIONS

  • Practice Question: What is a sign of disease or infection?

    • a) Headache

    • b) Fever of 39°C

    • c) Pain

    • d) All can be signs of disease.

  • Practice Question: Determine if the following diseases are communicable or noncommunicable based on their characteristics.
    1) Lung Cancer
    2) HIV

CONCEPT: VIRULENCE AND PATHOGENICITY

  • Virulence: Defines the degree of pathogenicity of an organism, indicating its ability to cause disease.

  • High pathogenicity: Associated with a greater likelihood of causing infections.

  • Virulence Factors: Traits that enable pathogens to cause disease (e.g., toxins).

PRACTICE QUESTIONS

  • Practice Question: Characteristics of a pathogen promoting pathogenicity are called:

    • a) Pathogen factors

    • b) Colonization factors

    • c) Infectious agents

    • d) Virulence factors

CONCEPT: STAGES OF INFECTIOUS DISEASE PROGRESSION

  • Infectious disease progression involves several stages:
    1) Incubation Period: Time from infection to the appearance of symptoms, varying by pathogen and host conditions.
    2) Prodromal Period: Initial vague symptoms like malaise.
    3) Period of Illness: Peak phase with strong symptoms.
    4) Period of Decline: Symptoms begin to decrease.
    5) Period of Convalescence: Recovery phase where the host eliminates the pathogen, although they may remain susceptible to secondary infections.

PRACTICE QUESTIONS

  • Practice Question: Identify the incubation period in the provided scenario involving Bob's exposure to Yersinia pestis.

    • a) January 10th - 21st

    • b) January 7th - 21st

    • c) January 7th - 9th

  • Practice Question: Identify the prodromal period in the provided scenario involving Bob's exposure.

    • a) January 10th - 11th

    • b) January 9th - 21st

    • c) January 7th - 21st

CONCEPT: KOCH’S POSTULATES

  • Koch’s Postulates: A series of criteria to determine the causative agents of diseases, leading to the identification of specific pathogens causing specific diseases (e.g., Bacillus anthracis for anthrax).

THE FOUR KOCH’S POSTULATES

1) The pathogenic microbe must be identified in every case of the disease.
2) The pathogen must be isolated and grown in pure culture.
3) The cultured pathogen should cause disease when introduced to a healthy organism.
4) The pathogen must be re-isolated from the experimentally infected host.

PRACTICE QUESTIONS

  • Practice Question: Limitations of Koch’s postulates include issues related to:

    • a) Diseases caused by viruses

    • b) Long latency periods post-infection

    • c) Asymptomatic carriers.

CONCEPT: MOLECULAR KOCH’S POSTULATES

  • Molecular Koch’s Postulates: A refined version introduced in 1988 by Stanley Falkow for identifying the specific cause of virulence in pathogenic microbes.

  • Unlike traditional Koch’s, they focus on the genetic and molecular mechanisms contributing to pathogenicity.

THREE MOLECULAR KOCH’S POSTULATES

PRACTICE QUESTIONS

  • Practice Question: Which of the following describes why Dr. Falkow developed molecular Koch’s postulates?

    • a) Original postulates had limitations.

    • b) Advancements in genetic technology and microbial studies.

    • c) Useful for detailed investigations of pathogen virulence.

CONCEPT: BACTERIAL PATHOGENESIS

  • Pathogenesis: The sequence of events that lead to disease development in a host.

  • There are several important steps in bacterial pathogenesis:
    1) Exposure to Pathogen: The initial encounter with the pathogen.
    2) Adhesion to Host: Involves binding to host cells using adhesin molecules (e.g., bacteria surface structures).
    3) Invasion: Pathogens must invade tissues or host cells to establish infection.
    4) Multiplication Inside Host: Pathogens multiply and damage host tissues.
    5) Evasion of Host Immune Responses: Pathogens must evade the immune system to survive and proliferate.

PRACTICE QUESTIONS

  • Practice Question: Which phase of bacterial pathogenesis refers to when pathogens multiply and begin damaging the host?

    • a) Local Infection

    • b) Focal Infection

    • c) Systematic Infection

CONCEPT: INTRODUCTION TO PATHOGENIC TOXINS

  • Certain pathogens produce toxins, which are biological poisons that enable them to invade and damage host tissues.

  • Toxigenicity: A pathogen's ability to produce toxins.

  • Toxins can be classified into two primary groups:
    1) Exotoxins: Soluble substances released during infection.
    2) Endotoxin: Lipopolysaccharide found in the outer membrane of gram-negative bacteria.

PRACTICE QUESTIONS

  • Practice Question: What are the characteristics of exotoxins?

    • a) Produce damage to specific tissues.

    • b) They can be categorized based on type (neurotoxins, enterotoxins, etc.).

CONCEPT: EXOTOXINS CAUSE DAMAGE TO THE HOST

  • Exotoxins: Highly specific toxins that may target tissues and cause various damages to cells.

  • Classification of exotoxins includes:
    1) Neurotoxins: Affect nervous system tissues.
    2) Enterotoxins: Damage gastrointestinal tissues, resulting in diarrhea or vomiting.
    3) Cytotoxins: Cause damage across different cell types.

PRACTICE QUESTIONS

  • Practice Question: The components of an exotoxin typically consist of:

    • a) Proteins

    • b) Amino acids

    • c) Lipids

CONCEPT: ENDOTOXINS

  • Endotoxins: Lipopolysaccharides found in the outer membrane of gram-negative bacteria, particularly Lipid A.

  • Lipid A can trigger systemic inflammatory responses leading to septic shock and other severe conditions.

PRACTICE QUESTIONS

  • Practice Question: What is the toxic component of lipopolysaccharide that poses threats during bacterial infections?

    • a) O-antigen

    • b) Lipid A

    • c) Core polysaccharide

CONCEPT: IMMUNE RESPONSE DAMAGE TO HOST

  • An overwhelming immune response can inadvertently damage the host's tissues.

  • The inflammatory response can result in unintentional damage due to recruitment of phagocytes, excessive fluid leakage, or destructive enzymes.

PRACTICE QUESTIONS

  • Practice Question: Which immune response scenario can inadvertently cause harm to host cells?

    • a) Severe inflammation leading to extensive tissue damage.

    • b) Phagocytic cells destroying pathogens but releasing their remains nearby.

CONCEPT: INTRODUCTION TO AVOIDING HOST DEFENSE MECHANISMS

  • Pathogens have developed various strategies to evade host defenses, including hiding within host cells or avoiding immune detection.

  • Some pathogens may choose to be phagocytosed, knowing that they can survive within the immune cells.

PRACTICE QUESTIONS

  • Practice Question: Why do pathogens hide within host cells?

    • a) Prevent exposure to immune cells.

CONCEPT: AVOIDING PHAGOCYTOSIS

  • Certain pathogens use mechanisms like producing enzymes that degrade immune proteins or forming capsules that block opsonization to avoid phagocytosis.

PRACTICE QUESTIONS

  • Practice Question: What do some pathogens produce to break down the immune protein C5a?

    • a) C5a peptidase.

CONCEPT: AVOIDING ANTIBODIES

  • Some bacteria can evade antibodies through mechanisms like producing proteases that degrade antibodies or undergoing antigenic variation to alter their surface structures to avoid recognition.

PRACTICE QUESTIONS

  • Practice Question: Antigenic variation allows pathogens to:

    • a) Alter their surface antigens to escape detection by antibodies.

CONCEPT: VIRUSES EVADE THE IMMUNE RESPONSE

  • To successfully replicate, many viruses employ strategies to evade host defenses, including preventing apoptosis, interfering with antigen presentation, and changing surface structures to avoid antibody recognition.

PRACTICE QUESTIONS

  • Practice Question: What do some viruses use to evade the immune response?

    • a) Antigenic variation.