Class notes
MBY 161 Theme 9 Notes
- Institution
- University Of Pretoria (UP)
This is a comprehensive and detailed note on theme 9; Microbial mechanisms of pathogenicity for MBY 161. Essential!! To your success in academics!!
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MBY 161 THEME 9: MICROBIAL MECHANISMS OF PATHOGENICITYLearning outcomes
Identify the principle ports of entry for a microorganism and describe how
microorganisms gain access through each
Explain the preferred portal of entry for a pathogen
Using examples describe how microbes adhere to cells
Explain how capsules, cell wall components and enzymes, and penetration
into the host cell cytoskeleton contribute to pathogenicity
List four methods that a bacterial pathogen can use to damage the host
cell
Describe the function of siderophores
Explain how toxigenicity differs from direct damage
Contrast the nature and effects of exotoxins and endotoxins
Microorganisms typically live in peaceful harmony with their host as part of the
normal microbiota
Typically, these microorganisms do not mean to cause disease
It is simply a way to obtain food and defend themselves against the environment
Portals of Entry
→ Mucous membranes (typically found in the respiratory, gastrointestinal,
genital system and the conjunctiva of the eyes)
o Typically, respiratory infections happen when microorganisms are
inhaled.
o Gastrointestinal entry occurs when we ingest food or water that has
been contaminated by microorganisms
, MBY 161 THEME 9: MICROBIAL MECHANISMS OF PATHOGENICITY
o Contact with the genital mucus membranes generally occurs through
sexually transmitted diseases
→ Skin (hair follicles, sweat glands)
o Skin is the largest organ of our body
o Unbroken skin is almost 100% impenetrable
o Microorganisms would thus use opens, such as a hair follicle or sweat
gland or wounds on the skins surface to obtain access through the skin
→ Parenteral route
o Normally when microorganisms are deposited underneath the skin
o Would usually happen when we have injury such as punctures or insect
bites that allow entry underneath the skin
Understand “Preferred portal of entry”
Microorganisms have a preferred portal.
They have a specific entry point in the body that they prefer to use and will not
always cause disease when encountering a different method or portal.
Numbers of Invading Microbes
The portal of entry is not the only factor that determines whether a microbe is
successful in establishing a disease or infection (ie. The number of invading
microbes is also important)
→ When we look at the portals for entry, we must also consider the number
of invading microbes
Two measurements used to describe this:
→ ID50: infectious dose for 50% of a sampled population
o Number of microbes that are able to infect 50% of a sample
→ LD50: lethal dose for 50% of the sampled population
o Used to describe the potency of a toxin
o Dosage that would kill 50% of the population
Practical example of the ID50 : Bacillus anthracis
PORTAL OF ENTRY ID50
Skin 10-50 endospores to cause disease
Inhalation 10 000- 20 000 endospores to cause
disease
Ingestion 250 000 – 1 000 000 endospores to
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