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Microbiology and Immunology 2500A/B Lecture Notes - Genitourinary System, Propionibacterium Acnes, Helicobacter Pylori

Microbiology and Immunology
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Lecture 1: Course Introduction 09/07/2012
Infectious Disease
The major cause of human mortality throughout history
Major increases in life expectancy from early 1900s mainly due to control
of infectious disease
Epidemiology of Infectious Disease
In large populations, an infectious disease may be able to find a continuous
supply of new hosts and becomes endemic i.e. continuously present
However, diseases in small populations cannot find sufficient new hosts and
‘burn’ themselves out
In smaller populations after a disease burns itself out, the non-immune population gradually builds up and may
become infected from outside to produce an epidemic i.e. affecting many people at the same time
An epidemic on an inter-continental scale is called a pandemic
Do Infectious Agents Evolve to Become More Virulent
There are multiple possible outcomes when a population is infected by a new infectious agent:
1. The host’s immune system overwhelms the agent
2. The agent overwhelms and kills the host without being transmitted
3. The agent replicates within the host and is transmitted to a new host. The host may die or recover.
New infections may produce a high death rate, but over the course of time the host and agent adapt to one
another and the disease normally becomes less virulent
Are Microorganisms Bad?
Modern medicine has studied microbes as perpetrators of disease
However, the vast majority of microorganisms are not pathogenic
In humans: about 1013-1014 resident microorganisms termed the microbiota mostly concentrated in the
gastrointestinal tract
Approximately more than 1000 different species, most have not been cultivated
The Human Microbiota
Internal organs are usually sterile
“Surface” tissues have extensive populations of microbes
The collective “genome” of the human microbiota (“the microbiome”) easily contains ≥ 100 times as many
genes as our own genome
The intestinal tract is the largest body surface in contact with the external environment (about 400 m2)
Some microorganisms are “entrenched” residents – the “core” microbiome
Others are “transient” that change due to food, water and other host and environment influences
Generally a poor bacterial habitat dry, salty, and constantly being shed
Bacteria that can grow on skin must be able to survive these conditions
Example: Propionibacterium acnes
o Live in sweat glands and hair follicles
o Difficult to eliminate by washing
o Cause acne when hormone activity in teenage years causes overproduction of fluid secretion
Example: Staphylococci
o Found on skin, they’re in the nasal region
o Major human pathogens
Oral Cavity
Saliva contains lysozyme and other enzymes that kill bacteria
Bacteria thrive when attached to teeth, especially in the gum margins
Example: Streptococcus mutans
o Secrete polysaccharides that adheres to teeth
o Production of acid wastes from fermentation of sugars causing tooth decay

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Genitourinary Tract
Upper genitourinary tract (kidney, bladder) is usually sterile
Lower part of urethra have some bacteria which are frequently washed out by urination
Vagina has a complex microbiota.
Example: Lactic acid bacteria (mostly Lactobacillus) produce lactic acid, maintain low pH of about 4.5
When this is disrupted (e.g. during antibiotic treatment), it can allow yeasts to grow
Gastrointestinal Tract
The intestinal tract is sterile at birth
Colonization starts in the birth canal
Complexity increases with age
Highly acidic (pH 2-3), most microbes cannot survive here
Some bacteria and yeasts can tolerate passage through stomach
Ulcers, long thought to be “stress disease”, now known to be due to Helicobacter pylori – found in more than
half of the human population
Small Intestine
Lower bacterial density at proximal portion, increases to distal portion
Approximately 108 cells/ml in distal small intestine
Large Intestine
Has enormous bacterial population (up to 100 trillion) of which the majority are obligate anaerobes
E. coli is less than 0.1% of total population
Is the Microbiota Good for Us?
Promotes a nutrient supply salvage energy from nutrients (particularly carbohydrates) that are otherwise non-
digestible by the host
Maintenance of normal mucosal immunity
Prevention of pathogen colonization
Human-Microbe Interactions
Parasitic: relationship between two species in which one benefits (parasite) from the other (host); usually
involves some detriment to the host
Commensal: relationship between two species in which one is benefited and the other is not affected, neither
negatively nor positively
Mutualistic: relationship between two species where both
Lecture 2: Introduction to Bacteriology 09/10/2012
The Domains of Life
Tree of life is based on genetic differences, not based on
It does not typically include acellular processes such as
Prokaryotes are the smallest, simplest, and most abundant cells on Earth
Prokaryotes include bacteria and archaea
Estimated 5 x 1030 prokaryotes on Earth
They lack a nucleus and complex organelles
Being Small has Advantages
Surface-to-Volume Ratio:
o Relatively larger surface area for nutrient exchange
o Grow faster/replicate more often
Bacteria evolve more quickly
o Smaller
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