Lecture 13: Infections
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Questions and Answers

Which portal of entry is most commonly associated with respiratory infections?

  • Skin
  • Mucous membranes (correct)
  • Conjunctiva
  • Genitourinary tract

Why is unbroken skin an effective barrier against pathogens?

  • It contains live cells that actively fight infections.
  • It allows easy passage for pathogens to enter.
  • The outer layer is made of water-soluble cells.
  • It consists of packed, dead skin cells. (correct)

What characteristic allows Neisseria gonorrhoeae to cause infection in one area but not another?

  • It requires a specific pH level to thrive.
  • It has a preferred portal of entry. (correct)
  • It can multiply quickly in different environments.
  • It can survive harsh environmental conditions.

What role does the placenta play in the context of microbial entry into the body?

<p>It allows nutrients but not pathogens to pass. (B)</p> Signup and view all the answers

Pathogens that enter through the gastrointestinal tract are typically resistant to what condition?

<p>Acidic pH of the stomach (D)</p> Signup and view all the answers

Which type of symbiotic relationship involves both species benefiting from the interaction?

<p>Mutualism (B)</p> Signup and view all the answers

What term describes bacteria that normally reside in the body and do not cause disease?

<p>Resident microbiota (B)</p> Signup and view all the answers

In which of the following sites would you expect an axenic environment?

<p>Kidney (C)</p> Signup and view all the answers

What can lead to normal flora becoming opportunistic pathogens?

<p>Immune suppression (B)</p> Signup and view all the answers

What is the primary reason for the overgrowth of C. difficile after antibiotics?

<p>Decreased microbial antagonism (D)</p> Signup and view all the answers

Which of these describes transient microbiota?

<p>Bacteria that are present temporarily (A)</p> Signup and view all the answers

Which of the following is an example of parasitism?

<p>Parasites harming their hosts while benefiting (C)</p> Signup and view all the answers

Why might a patient with AIDS be more susceptible to certain infections?

<p>Weakened immune defenses (B)</p> Signup and view all the answers

Which of the following pathogens has the highest likelihood of crossing the placenta?

<p>Toxoplasma gondii (B)</p> Signup and view all the answers

What does the ID50 value indicate about a pathogen?

<p>The number of organisms required for 50% of subjects to show infection (A)</p> Signup and view all the answers

Which condition is NOT a potential result of a pathogen crossing the placenta?

<p>Chronic illness in the mother (B)</p> Signup and view all the answers

What is the most common nosocomial infection?

<p>Urinary tract infection (UTI) (D)</p> Signup and view all the answers

Which of the following agents is NOT commonly associated with opportunistic infections in seriously ill patients?

<p>Bordetella pertussis (D)</p> Signup and view all the answers

What role does the epidemiology of a disease primarily play?

<p>Studying the occurrence, distribution, and spread of disease (D)</p> Signup and view all the answers

Which bacterial agent has the lowest ID50 value, indicating higher virulence?

<p>Legionella (D)</p> Signup and view all the answers

What is a common pathway for pathogens to gain entry into the body?

<p>Parenteral routes such as broken skin (C)</p> Signup and view all the answers

Study Notes

Symbiosis

  • Symbiosis is a close relationship between different species
  • Commensalism - Two species coexist without any effect on each other
  • Mutualism - Two species benefit from their relationship
  • Parasitism - One species benefits from an association to the detriment of the other

Normal Microbiota

  • Also known as normal flora or indigenous microbiota
  • Colonize the body from birth
  • Most are non-pathogenic
  • Resident microbiota remain throughout life
  • Transient microbiota remain for a limited time

Axenic Sites

  • Axenic means sterile, free from foreign organisms
  • Examples include:
    • In utero
    • Kidney
    • Prostate
    • Middle and inner ear

Opportunistic Pathogens

  • Normal microbiota can become pathogenic under certain conditions
  • Immune suppression can lead to infections by organisms that wouldn't normally cause disease
  • Location change of microbiota can lead to infection in unusual areas
  • Changes in relative number of normal flora can also lead to disease
    • Microbial antagonism usually prevents overgrowth of one type of normal flora
    • Overgrowth of one type can lead to disease

Portal of Entry

  • Pathogens enter the body through various portals of entry
  • Some pathogens have preferred portals of entry
  • Examples of portals of entry:
    • Mucous membranes
    • Skin
    • Placenta
    • Parenteral route

Mucous Membranes

  • Line body openings and provide a moist, warm environment for pathogens
  • Respiratory tract is the most common site of entry
  • Gastrointestinal tract is another route, some pathogens survive stomach acid
  • Genitourinary tract (UTI, STI)
  • Conjunctiva (viruses can enter the respiratory tract through the eyes)

Skin

  • Acts as a barrier against pathogens due to its outer layer of dead cells
  • Unbroken skin is a good defense
  • Some fungi grow on the skin
  • Pathogens can enter through openings (sweat glands, hair follicles)
  • Others enter by burrowing into or digesting the skin (hookworms, Schistosomes)

Placenta

  • Forms a barrier to most pathogens
  • Some pathogens can cross the placenta and infect the fetus, causing:
    • Spontaneous abortion
    • Birth defects
    • Premature birth

Parenteral Route

  • Pathogens gain access via broken skin
    • Injections
    • Punctures
    • Bites
    • Cuts, wounds
    • Surgery
    • Cracking/splitting of skin

Measures of Pathogenicity

  • LD50 (Lethal Dose 50): the number of microbes that kill 50% of test animals
  • ID50 (Infectious Dose 50): the number of microbes required to produce demonstrable infection in 50% of test animals

Common Nosocomial Infections

  • Nosocomial infections are acquired in healthcare settings
  • Urinary tract infection (UTI) is the most common nosocomial infection
  • Lower respiratory tract infection (LRTI) including bronchitis, tracheitis, pneumonia
  • Surgical wound infection
  • Bloodstream infection

Epidemiology

  • Study of the occurrence, distribution, and spread of disease
  • Etiology of disease:
    • Causative agent
    • Mode of transmission
    • Geographical distribution

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Infections Lecture Notes PDF

Description

This quiz explores the intricate relationships between different species, such as commensalism, mutualism, and parasitism. It also covers the concept of normal microbiota, their roles in health, and the conditions under which they can become opportunistic pathogens. Test your understanding of these critical microbiological concepts.

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