• Three basic types
(1) Eukaryotes have a nucleus and membranous organelles. Includes protozoa and fungi
(2) Prokaryotes don’t have a nucleus or membranous organelles. Includes bacteria and archaea
(3) Viruses non-living packets of DNA
• Very rapid
• Can divide every 20 minutes
• High rate of reproduction has allowed microbes to evolve many species and rapidly adapt to extreme conditions
1

• Disease causing microbes
• 5 to 10 times smaller than human cells
• Can absorb nutrients rapidly because of their large surface to volume ratio
• Have a plasma membrane
• Lack membranous organelles
• Have a single ring of DNA
• Found in different shapes including:
- spherical
- rod shaped
- curve shaped (like a spring)
2

Spherical shaped bacteria (cocci)
3

• Have a rigid cell wall that surrounds the plasma membrane
• Have external structures such as:
- capsules for protection
- flagella for movement
- pili for attaching to tissue cells (example the gonorrhea bacteria attaches to cells of the urinary tract
• Eukaryotic cells with a cell wall that is not affected by antibiotics
• Release spores in large numbers
• Secrete digestive enzymes that breaks down the substrate they are on (example is athlete’s foot)
• Over 100,000 species of which 100 cause human diseases like ringworm and yeast infections
• Passed on by air, soil, dust, or contact
4

• Most are single-celled eukaryotes that have cilia, pseudopodia, or flagella for movement
• 20,000 species known – 30 cause human diseases
• Under drought conditions can form cysts that live for centuries
• Consist of a molecule of DNA or RNA surrounded by a protein coat
• Lack organelles and energy enzymes needed for growth and reproduction
• Must enter a host cell to reproduce
• Host cell reproduces the virus
5

• Some live in or on the human body and are called normal flora. These include
E.coli bacteria that live in the colon and help us digest food, produce vitamins, and defend against other pathogens
• Medical products include antibiotics, vaccines, hormones, and steroids
• Food products include yogurt, buttermilk, sour cream, cheese, beer, wine, and bread
Microbes working in the environment
• Photosynthetic produce oxygen for the environment and sugars for the food chain
• Decomposers break down dead organics to release carbon dioxide and nitrogen
6

• Are capable of growing in tissue and causing diseases
• Most are mild and easily controlled by our immune system
• Others like rabies, cholera, and plaque can overwhelm our immune system
• Some only infect us when our immune system is down (like during AIDS)
How do pathogens enter the body
• Through portals of entry such as breaks in the skin or exposed mucous membranes such as the eye or mouth
• Some (like the cold virus) enter only through one port (like the nose or mouth)
• Passed directly from an infected host
• By contact with contaminated objects
• By almost any means imaginable
7

• Are those disease that can be passed directly or indirectly from another host.
Examples: colds, flu, AIDS
• Are not acquired directly or indirectly from another animal. Examples: gas gangrene, botulism, tetanus
• They enter a tissue area, multiply in number, and cause tissue damage
• Tissue damage alters the physiology and produces the symptoms of the disease
8

• Reproduce and release enzymes and chemical toxins that help them invade and destroy tissues that then provide them with nutrients
• There are two categories of bacterial toxins
(1) Those from living bacteria
(2) Those from dead, disintegrating bacteria
• Cholera enter the G.I. tract with contaminated food or water. They produce a toxin that irritates the lining of the tract leading to diarrhea
• Tetanus bacteria enter through a wound.
They produce a toxin that affects the nerves going to muscles – leading to spasms
• Salmonellosis secretes a toxin that can cause fever, weakness, intestinal bleeding, and even shock
• Heating the food wont have any affect because the bacteria are already dead
9

• Reproduce by entering a host cell
• The host cell reproduces the virus
• Symptoms of viral disease depends on the type of host cell infected
• Are similar to bacteria in their methods of infection
• The release enzymes and chemical toxins to invade and digest tissues
• Pathogenic fungi get into the body through:
(1) The respiratory system (like histoplasmosis from bird droppings
(2) The skin (like ringworm and athletes foot)
10

• Infect the G.I. tract (amoebic dysentery
Giardia), brain, liver, and blood (malaria)
• The life cycle of the malaria parasite is shown on the next slide
• The protozoan enters the body through mosquito bite and infects the red blood cells
Life Cycle of the Protozoan that causes malaria
• Sterilization destroys all microbes
• Pasteurization reduces their numbers significantly
• Physical methods temperature, moisture, and pH can destroy microbes
• Chemical methods
disinfectants are used on non-living surfaces
- antiseptics are used on living surfaces
11

• Interfere with cellular processes and structures unique to bacteria. Example:
- penicillin interferes with the production of bacterial cell walls
- tetracycline and erythromycin inhibit bacterial protein synthesis
• Over use of antibiotics has led to the evolution of bacteria that are immune to those antibiotics
• New antibiotics must be produced that these microbes have never encountered
12