MICROM 301 Lecture Notes - Lecture 4: Phagocytosis, Viremia, Microvillus
Independent Study - Mechanisms of Pathogenicity I. The Anatomical Barriers as
Ecosystems (SECTION 16.1)
•Mutualism
oBoth partners benefit
•Commensalism
oOne partner benefits and the other remains unharmed or benefited
•Parasitism
oOne organism (the parasite) benefits at the expense of the other
II. The Normal Microbiota (aka Normal Flora) (SECTION 16.2)
The protective role of the normal microbiota - Clostridium difficile example
-Normal microbiota: population of microorganisms normally found growing on healthy individuals
-When normal microbiota are killed / growth is suppressed (ex. antibiotic treatment), pathogens
may be able to colonize and cause disease
oClostridium difficile example:
Oral antibiotics inhibit members of normal intestinal microbiota
Overgrowth of toxin-producing strains of Clostridium difficile
Causes antibiotic associated diarrhea and colitis
The dynamic nature of the normal microbiota
-Protection against infection
-Promoting oral tolerance
-Aiding digestion
-Producing substances important for human health
III. Principles of Infectious Disease (intro to CHAPTER 16; SECTION 16.3) Terms to note
Colonization: a microbe establishing itself and multiplying in a particular environment
Infection: if the microbe has a parasitic relationship with the host
subclinical infection: symptoms either do not appear, or are mild enough to go unnoticed
disease: a condition that prevents the body from functioning normally
primary infection: initial infection
secondary infection: additional infection that occurs as a result of the primary infection
primary pathogen (pathogen): a microbe or virus that causes disease to an otherwise healthy individual
opportunistic pathogen (opportunist); example - Pseudomonas aeruginosa: causes disease ONLY
when the body’s innate or adaptive defenses are compromised OR when introduced into an unusual
location
example = environmental bacteria that routinely come into contact with healthy
individuals without harmful effect
can cause fatal infections in individuals who have the genetic disease cystic
fibrosis and also in burn patients
virulence
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infectious dose
ID50:The number of microbial cells administered (dose) that resulted in disease in 50% of the population
The course of infectious diseases (FIGURE 16.2) - Incubation period, illness, convalescence carriers
Duration of symptoms - acute, chronic, and latent infections
Distribution of pathogens - localized, systemic, disseminated, bacteremia, sepsis, toxemia, viremia IV.
Overview of Pathogenesis (Intro to section on Mechanisms of Pathogenesis: p. 420 - 421)
Production of toxins that are then ingested
Colonization of mucous membrane of the host, followed by toxin production
Invasion of host tissues
Invasion of host tissues followed by toxin production
Mechanisms of Pathogenesis:
1. Production of toxins that are then ingested
2. Colonization of a mucous membrane of the host, followed by toxin production
a. Microbe has ability to adhere to mucous membrane – multiply to high numbers
– produce toxin
3. Invasion of host tissues
a. Microbe penetrates first line of defense – multiply within tissues
b. Able to avoid immune system
4. Invasion of host tissues, followed by toxin production
a. Avoid immune system
b. Produce toxin that inhibits cell function
Establishment of Infection:
-Adherence:
oAdhesins
Pili (fimbriae)
Host cells have receptors for specific molecules (pili on bacterial cells)
-Colonization:
oUsually done on a mucous membrane first
oCompete with normal microbiota
Usually protects by covering binding sites
oObtain iron
Siderophores
Secreted proteins from bacteria that bind iron and bring it back to
bacteria
High affinity for iron – can do this successfully
Most bacteria secrete some form of siderophores
oAvoid IgA
Secretory IgA – protects mucosal surfaces
find more resources at oneclass.com
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Document Summary
Ecosystems (section 16. 1: mutualism, both partners benefit, commensalism, one partner benefits and the other remains unharmed or benefited. Parasitism: one organism (the parasite) benefits at the expense of the other. The normal microbiota (aka normal flora) (section 16. 2) The protective role of the normal microbiota - clostridium difficile example. Normal microbiota: population of microorganisms normally found growing on healthy individuals. When normal microbiota are killed / growth is suppressed (ex. antibiotic treatment), pathogens may be able to colonize and cause disease: clostridium difficile example: Oral antibiotics inhibit members of normal intestinal microbiota. Overgrowth of toxin-producing strains of clostridium difficile. Principles of infectious disease (intro to chapter 16; section 16. 3) terms to note. Colonization: a microbe establishing itself and multiplying in a particular environment. 50:the number of microbial cells administered (dose) that resulted in disease in 50% of the population. The course of infectious diseases (figure 16. 2) - incubation period, illness, convalescence carriers.
