microbiology unit 4
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how does the microbe enter your body?
- Portals of Entry
- •Mucus membranes
–entry: mouth, nose, UG
–some grow on membrane surface
•cell products may penetrate (C.diphthereae)
–some penetrate mucus membranes and infect deeper tissues
2 types of Portals of Entry:
1. •Skin - very effective barrier when intact
–entry through cuts, hair follicles, sweat gland ducts, cornea
2. •Parenteral - direct deposition beneath skin
–bites, cuts, biological vectors, injections
Many have preferred portal that is required for infection
–Based on tissue type to which they must initially attach or avoidance of host defenses
•Ex: Rickettsia rickettseae
•Some with more than one preferred portal.
–Example: Yersinia pestis
•Bubonic – parenteral
Pneumonic – via respiratory tract (inhalation
Size of the Initial Inoculum will affect the risk of infection and disease how?
Entry of more cells will increase the risk of infection and disease
What Is the ID50:
Number of cells enterthing that results in 50% probability of infection and diesease test subjects:
probability of infection and diesease test subject:
1.) portal effect?
- 1.) Anthrax endospores
- -skin: 10-50 endospores
- -inhalation: 10,000-20,000 endospores
- -gastointestinal: 250,000 endospores
–Other conditions can influence ID50?
>•Example: Vibrio cholereae
–108 with normal stomach pH
–Much lower after neutralization with bicarbonate
What is LD50?
Is it usually greater or less than the ID50?
1. Lethal dose for 50% of sample population
2. Greater than ID50
What would you like to do?
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