Microbiology Chapter 19.txt

Invasion of a host by a parasite

Any change from good health

• the relationship between the host and microbe
• the competition for supremacy between them
• If the host loses the competition, disease occurs

Intestines, mouth, skin, vagina

• During passage thru birth canal
• Contact with feeding materials
• Contact with medical instruments
• Contact with other people
• During nursing

Microbes that reside in the body without causing disease (in symbiosis)

• Micronutrients
• Vitamin K

Commensalism

Both host and microbe benefit

• The microbe benefits and the host is unaffected.
• This is not very common

Ability to invade the body and cause disease

Damage and disease in the host

• The degree of pathogenicity
• Severity of disease

A pathogen breaches the host�s external defense and enters sterile tissue

normal microbiota enter sterile tissue

Commensals take advantage of a change in the body�s environment that favors the microbe

A parasite that causes no harm to the host.

Acute diseases develop rapidly, cause severe symptoms, and fade quickly

Chronic diseases linger for long periods of time, and are slower to develop and recede

Local and systemic diseases

Can invade and cause disease in a healthy body

Infections in someone who has another disease

Infection in a specific area, such as a boil

Systemic diseases disseminate to organs and systems

• Incubation
• Prodromal symptoms
• Acme
• Decline
• Convalescence

The time between entry and appearance of symptoms

• Number of organisms that entered host
• Generation time
• Virulence
• Host resistance
• Location of entry

• General symptoms
• Malaise
• Nausea
• Headache

• Pinacle
• Peak of disease
• Specific symptoms appear
• Crisis period
• If you make it thru, you live

Body has won the fight and is killing off stragglers

Regain strength and return to normal

Symptoms are apparent

• Symptoms are minor
• Few obvious symptoms

• Skin
• Mucous membranes
• Eyes � lysozymes
• Saliva

• The portal of entry is the route an exogenous pathogen uses to enter the body
• Area where the disease enters
• Has to be the right entry or disease is not established.
• IE, tetanus must enter a puncture wound, not the stomach to cause disease

• The infectious dose is the number of microbes entering the body
• You need to get the minimum required bacteria.
• IE, cholera you need at least a million bacteria to become infected
• If you have a high level of resistance, you need more

Many pathogens have adhesins that allow then to adhere to specific tissues

The ability of a pathogen to penetrate tissues and spread

Enter cells or pass through defenses

to produce toxins

The presence of toxins in the blood

Proteins produced during bacterial metabolism

The nervous system

The gastrointestinal tract

Produced by the host body and neutralize toxins

Toxins whose toxicity has been destroyed but still elicit an immune response

• Released upon disintegration of gram-negative cells
• They cause blood coagulation and cell rupture

• Increased temperature
• Body weakness
• Aches
• General malaise
• Damage to the cardiovascular system

• Blood pressure drops due to the endotoxins causing blood vessels to dialate
• May occur with antibiotic treatment of diseases caused by gram-negative bacilli

• Can increase virulence
• Some organisms make enzymes that increase their chances of causing disease
• Leukocidins
• Hemolysins
• Coagulase
• Streptokinase
• Hyaluronidase

• Enhances pathogen penetration through tissues
• Destroys hyaluronic acid, a polysaccharide that "cements" cells together in a tissue
• Permits organisms to spread through tissues and establish themselves at sites distant from that of the intial infection

Some staphylococci produce streptokinase, which dissolves fibrin clots and allows dissemination of the bacteria

• Destroy white blood cells
• Disintegrate neutrophils and macrophages

Dissolve red blood cells

Some staphylococci produce coagulase to form a blood clot that protects them from phagocytosis

Weaken or harm the host body

• increase the virulence of a pathogen
• Enzymes influence virulence

• A layer of bacteria
• Virulence can be enhanced in biofilms because immune cells cannot reach bacterial cells

• Cough or sneeze
• Urine
• Blood
• Insect bite
• Feces
• Lesion

• Person to person contact
• Coughing
• Animal bite

• Fomites
• Arthropod vectors
• Mechanical vectors: bug lands in feces and then later in food
• Biological vectors: Organism lives in the bug. Bug poops on you
• Reservoirs
• Carriers

Bug lands in feces and then later in food

Organism lives in the bug. Bug poops on you

Ecological niches where microbes live and reproduce

Have recovered from the disease but continue to shed the disease agents

• Are contagious
• They are transmittable among hosts in a population

• Not easily transmitted to another host
• They are acquired directly from the environment

Is habitually present at a low level in a certain geographic area

Occurs in a region in excess of what is normally found in that population

A more contained epidemic

A worldwide epidemic

Means that diseases emerging anywhere in the world can be spread globally

Diseases transmitted from other vertebrate animals to humans

Hospital acquired

Occur as a result of receiving treatment for another condition

• Changes in land use or agriculture practices
• Changes in human demographics
• Poor population health
• Pathogen evolution
• Contamination of food sources and water supplies
• International travel
• Failure of public health systems
• International trade
• Climate change