Course Introduction and Introduction to Bacteriology

6 Pages
Unlock Document

Microbiology and Immunology
Microbiology and Immunology 2500A/B

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 10 -10 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 2  The intestinal tract is the largest bodysurface in contact with the external environment (about 400m )  Some microorganisms are “entrenched” residents – the “core” microbiome  Others are “transient” that change due to food, water and other host and environment influences Skin  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 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 Stomach  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 8  Approximately 10 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 benefit Lecture 2: Introduction to Bacteriology 09/10/2012 The Domains of Life  Tree of life is based on genetic differences, not based on characteristics  It does not typically include acellular processes such as viruses Prokaryotes  Prokaryotes are the smallest, simplest, and most abundant cells on Earth  Prokaryotes include bacteria and archaea  Estimated 5 x 10 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 o Haploid genome (one set of chromosomes) Bacteria Can Grow Fast  Bact
More Less

Related notes for Microbiology and Immunology 2500A/B

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.