Host-Pathogen Interaction Lecture 7

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Questions and Answers

What role do bacterial normal flora play in the formation of antibodies?

They directly produce antibodies against pathogens.

They enhance blood clotting mechanisms.

They stimulate the production of antibodies against ABO blood antigens. (correct)

They prevent the formation of blood type antigens.

Which of the following factors is NOT a component of bacterial virulence?

Capsule

Antibiotic susceptibility (correct)

Glycocalyx

Fimbriae

What is the definition of pathogenicity in microorganisms?

The ability to resist antibiotic treatment.

The degree of infection caused by parasites.

The capacity of bacteria to replicate quickly.

The ability of a microorganism to cause infection. (correct)

Which mechanism allows bacteria to evade host defenses?

Genetic traits enhancing infection capability. Signup and view all the answers

In which system can bacteria transiently colonize due to upstream migration?

Genitourinary system Signup and view all the answers

What is the main reason not all infections result in disease?

Not all pathogens have the potential to cause disease. Signup and view all the answers

Which organism is classified as an overt pathogen?

Mycobacterium tuberculosis Signup and view all the answers

What defines an opportunistic pathogen?

It requires a compromised host to cause disease. Signup and view all the answers

What role does MRSA play in the case of recurrent dermatitis for the 20-year-old female?

It is an opportunistic pathogen responsible for infection. Signup and view all the answers

What classification does Aspergillus niger fall under when it causes fungal pneumonia in an immunocompromised person?

Opportunistic pathogen Signup and view all the answers

In the context of normal flora, which statement is true?

Normal flora generally do not cause disease and can protect against pathogens. Signup and view all the answers

What can increase an individual's susceptibility to diseases caused by opportunistic pathogens?

Being immunocompromised or having a weakened immune system Signup and view all the answers

What is a characteristic of normal flora in the human body?

They can cause disease under certain conditions. Signup and view all the answers

What is the role of normal flora in stimulating the immune system?

They stimulate antibody formation that can react with pathogens. Signup and view all the answers

Which bacterial factor significantly influences susceptibility to infection?

Bacterial infective dose. Signup and view all the answers

Which of the following correctly describes virulent strains of bacteria?

They have a higher capability to cause disease compared to less virulent strains. Signup and view all the answers

Infections caused by bacteria found outside normal flora are termed what?

Exogenous infections. Signup and view all the answers

Which of the following sites is considered normally sterile in the human body?

Blood. Signup and view all the answers

What does the presence of bacteria in the blood indicate in an immunocompromised patient?

It must be considered a disease. Signup and view all the answers

Which statement about opportunistic pathogens is correct?

They can cause infections when the host's defenses are compromised. Signup and view all the answers

Which of the following statements about the protective effects of normal flora is true?

Normal flora competes with pathogens for space and resources. Signup and view all the answers

Which factor does not affect susceptibility to bacterial infections?

Weather patterns. Signup and view all the answers

Study Notes

Host-Pathogen Interaction (I)

Lecture 7, Dr. Mohamed El-Azizi
Course material covers Host-Pathogen Interaction
Learning objectives include defining infection, disease and colonization.
Recognizing the role of human microbiota
Understanding the relationship between bacterial pathogenicity and host immunity
Differentiating pathogenic bacteria from opportunistic bacteria
Analyzing clinical case studies for bacterial infection diagnoses & interventions
Applying host-pathogen relationship in patient counseling
Differentiating nosocomial and community-acquired infections

Learning Outcomes

Students will be able to define infection, disease, and colonization
Students will know the role of normal flora in the human body
Students will grasp the relation between bacterial pathogenicity and host immunity
Students will differentiate pathogenic bacteria from opportunistic bacteria
Students will analyze clinical cases correlating to bacterial infections, recommending ideal interventions.
Students will apply the host-pathogen relationship in patient counseling.
Students will distinguish nosocomial from community-acquired infections

Textbooks and Resources

Patrick Murray et al. Medical Microbiology, 5th ed., 2007
10 copies available in the library
Access to online resources with username/password (university only)

Bacteria Classification

Bacteria are categorized as "Good", "Bad", and "Ugly"
Good bacteria: non-pathogenic, produce antibiotics, valuable industrial products.
Bad bacteria: cause illness with low/no mortality in healthy individuals. Many common disease-causing bacteria (e.g., Staphylococcus aureus, Shigella)
Ugly bacteria: cause high mortality in untreated individuals; severe diseases resulting from Bacillus anthracis, Vibrio cholera, Clostridium tetani.
Pathogenic bacteria can be further categorized as Overt Pathogen or Opportunistic
- Overt pathogens: they cause disease in healthy hosts
- Opportunistic pathogens: cause disease in compromised hosts
Normal Flora (Symbiosis): coexist with the host without harm or benefit.
Mutualistic & Commensal: types of normal flora

Disease

Damage caused by microorganisms/their products.
Symptoms are triggered by microorganisms presence
Bacteria cause disease by:
- Microorganism in the host eliciting immune/inflammatory response, causing damage.
- Organism proliferation (damage).
- Damage by microbial products (e.g., enzymes, toxins, acids, gases).
- Absorption of proteins/amino acids via tissue degradation

Infection

Presence of a microorganism, not necessarily causing disease.
- Can occur without symptoms
Many bacteria can cause infection but can't trigger disease.
Infection in a patient is always indicative of disease.

Colonization

Presence of microorganisms without disease.
Usually, antibiotics are not needed.
Applies to surfaces, not usually the blood.
Differentiate from disease states (e.g. symptoms appear and infection ensues)
Colonization vs. infection: colonization isn't always bad, disease results when bacteria are in sites they shouldn't be or are causing harm.

Factors affecting susceptibility to infection

Bacterial infective dose (e.g., Shigella, Vibrio cholera)
Bacterial strain (virulence levels)
Host factors (e.g., immune status, route of entry)

Normal Flora

Microorganisms frequently found in healthy subjects
Can cause disease under specific conditions (unprotected sterile sites).
Infections from normal flora are called endogenous infections.
Infections from other bacteria are known as exogenous infections.
Body sites colonized by normal flora (e.g., GI tract, upper respiratory tract, distal genitourinary tract, skin).
Body sites typically sterile (e.g., blood, CSF, interstitial fluid, lymph, organs)

Normal Flora - Examples

Skin: Staphylococcus aureus, Staphylococcus epidermidis
Stomach: Helicobacter pylori (gastritis/ulcers)
Large Intestine: E. coli, Bacteroides fragilis
Genitourinary system: Anterior urethra, urinary bladder

Pathogenic Bacteria

Ability to cause infection/disease in a host.
Virulence factors (traits like capsule, fimbriae, glycocalyx) enhance ability to cause disease.
- Facilitates spread, multiplication, immune system evasion, damage to tissues,transmission.

Factors affecting normal flora

Environment (e.g., hospitalizations, replacement of bacteria)
Host health
Broad-spectrum antibiotics: can negatively affect the normal flora.

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Description

This quiz focuses on the fundamental concepts of host-pathogen interactions as discussed in Lecture 7 by Dr. Mohamed El-Azizi. Students will test their understanding of infection, disease, and colonization while recognizing the role of human microbiota and differentiating between pathogenic and opportunistic bacteria. Clinical case analyses will also be explored to apply this knowledge in real-world scenarios.