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living organism that transmits infectious agen from 1 host to another, most are biting or blood sucking insects, malaria-mosquitos, ticks-RMSF

Portal of entry

how MO gets into host, mouth, nose, vagina, penis, wound

Oppurtunistic MO

MO takes advantage of the situation or opportunity that it normally does not have to cause a disease
Clostridium difficile, Staph aureus in surgical wound infection


interaction of 2 or more species in some ongoing way


infection found in animals but naturally transmitted to humans, rabies, anthrax, plague

Typhoid Mary

-Mary Mallon was the 1st known healthy carrier or typhoid fever
-Worked as a cook. As a result, infected hundreds of people
-Vehemently denied she was the cause of illness
-Was quarantined
-Upon her death, autopsy revealed gallbladder to be filled with typhoid-causing bacteria

Human Habitat

Idea Habitat for MO because of good source of nutrients and moisture, stable pH, right temperature, and large surface area on which to settle

Normal Resident Flora

large, mixed population of MO adapted to our body, generally good for us, everyone has a different resident flora
About 100 trillon MO
Largest in colon and gums in mouth, one trillion MO/gram
Skin 100,000 MO/gram
Nose 10,000 MO/gram
Also a wide diversity of MO
500 different in human feces
200 different MO in mouth
MO may be bacteria, fungi, protozoan
Helpful in many ways, Vitamin K in intestines, competition for nutrients
Colonized at birth

Transient Flora

MO on or in body for a short time, passing through

Skin as a Habitat

Largest organ system in body
MO usually on surface and epidermis, intact
Staph Aureus, Staph Epi, fungi

Respiratory Tract as a Habitat

MO in upper respiratory tract
Should NOT find MO in lower tract
Most MO filtered out by nasal hairs
Staph, Haemophilus, Neisseria

GI Tract as a Habitat

MO from mouth to anus
Few MO in esophagus and stomach
Many MO important
E.Coli, Enterobacter, Closteridium, Citrobacater

Urogenital Tract as a Habitat

MO mostly outer surfaces of penis and vagina
May find MO in lower urogenital tract
Should NOT find MO in upper tract
Strep, Coliforms, Staph

Where you should not find MO in Human Body

Blood, Spinal Fluid, Synovial Fluid, Urine


anything that houses a MO, plants, animals, insects, human


MO that is capable of causing a disease
Salmonella and Corynebacterium


MO that does not cause a disease
Micrococcus luteus


potency of pathogen, how powerful is pathogen, 4 classes

Class 1 Virulence

low virulence, not know to cause a disease
Micrococcus luteus

Class 2 Virulence

moderate risk to cause a disease
Staph aureua

Class 3 Virulence

MO readily transmitted and virulent
Mycobacterium tuberculosis

Class 4 Virulence

deadliest of the MOs
Ebola, Marburg virus, Lassa Fever, Rabies
Need bio containment facilities to work with Class 4 MO

Low Virulence

high numbers-disease

High Virulence

low numbers
Ebola, and Tularemia




development sequence a disease goes through, transmission, entrance, incubation, symptoms, prognosis


occurs when MO overcomes body's defenses and lives inside host, may or may not cause tissue damage


conditions where host's tissues are damaged or function is altered

Clinical Infection

signs or symptoms of disease are seen: fever, redness, swelling, open wounds

Subclinical Infection

no apparent signs or symptoms seen, most dangerous stage of disease


host with clinical or subclinical infection who carries disease from one location to another
Typhoid Mary


MO established on body surface

Acute Infection

infection that comes on rapidly, with severe but short-lived side effects
Flu and common cold

Chronic Infection

infection that progesses and persists over a long period of time
TB and syphilis

Sub-Acute Infection

infection that does not come on as rapidly as acute infections or persist as long as chronic ones
Walking pneumonia

Secondary Infection

infection that compounds a preexisting infection

Mixed Infection

several MO establish themselves simultaneously at infection site
Staph & Strep-infection of the mouth

Baterialremia & Viralremia

small numbers of bacterial/virus in the blood but not necessarily multiplying


MO are multiplying in the blood and are present in large numbers


primary habitat in the natural world from which a pathogen originates
insects, animals, soil, water, rabies-bats, water-cholera, plague-rats


relationship that is helpful to organism but causes no damage to the host


relationship that is beneficial to both host and organism
bacteria in stomach of termite


organism lives in or on host and gets its livelihood from host and causes harm to host
tapeworm, roundworm in GI tract

Comprimised host

host whose natural defense mechanisms are impaired or suppressed, medical treatment (radiation treatment), stress, other illness (flu followed by pneumonia) inborn errors of metabolism

Contagious Disease

the ability of a pathogen to multiply in host, exit from host, be transmitted to 1 or more secondary host, enter and cause a disease in the secondary host, sometimes called communicable disease

5 Routes of Transmission & Entry of MO into Host

Airborne Spread
Common Vehicle Spread
Vector Borne Spread-Mechanical or Biting
Contact-Direct, Indirect, Droplet, Fecal Oral Route
Endogenous-self spread

Airborne Spread

Spread of MO over a distance of more than several feet between the source and the victim, Anthrax
MO contained in very tiny droplets, may stay suspended for hours or days
Laughing, Coughing, Singing, Shouting, Talking, Spiting, Sneezing, anything propelling out of the mouth

Common Vehicle Spread

Contaminated inanimate vehicle acts as a means of transmitting MO to several people
Glass, cups, knives, spoon, forks, any objects that can be placed in mouth

Vector Borne Spread

Mechanical spread of MO on hairs on insects to inanimate objects, food, people
Most insects are very hairy creatures
Biting transfer by blood sucking insects or by biting animals to other hosts
Mosquitos, ticks, fleas, dogs, raccoons, skunks, bats

Contact Spread

Prospective host must have actual contact with the source of the MO and the primary host

Direct Contact

person to person spread, actual physical contact, syphilis, gonorrhea, HIV, kissing, touching, sexual contact, handshaking

Indirect Contact

Passive spread of MO through an intermediated object, doorknob, light switch, elevator button

Droplet Spread

airborne spread of MO when source and victim are relatively close to each other, in your face, sneezing, coughing, talking

Fecal Oral Route Transmission

Inadequate personal hygiene after defecation, unclean drinking water, salad bars, sandwich bars, may be direct or indirect

To be a successful pathogen MO must do 4 things (Possible Discussion Question)

1. Survive passage from 1 host to another host or from reservoir to host, animal, direct contact, environmental conditions-hot/cold
2. Attach or penetrate into host's tissue, abrasions, injection, ingestion, incision, scrapes, cuts, catherizations
3. Withstand host's defense mechanisms-1st line of defense (external mechanisms), 2nd line of defense (internal mechanisms), 3rd line of defense (immunity)
4. Induce damage to or malfunction of host's tissues, toxins, damaging neural muscular junctions, pneumonia in lungs

MO Pathogenicity

Attachment, Receptor sites not full, Fimbriae, Capsules, Spikes, Hooks, Filament

Circumvention of defense mechanisms

capsules, inhibits phagocytosis, Leukocidin destroys WBC

Hyaluronic acids

destroys tissue cement


dissolves blood clots


destroys collagen in bone, muscles, and cartilage


destroy RBC


inhibits phagocytosis by putting fibrin on cell wall of MO


tissue damage or malfunction of tissue

Stimulation of Vigorous Inflammatory Response

response that changes function of host cells
Strept. pneumona for TB forming scar tissues in lung

Secretion of enzymes by MO

collagenase, hemolysins, lipases, nucleases, etc.


toxins released into surrounding environment when MO dies, less potent, larger amounts of toxins need to cause problems such as fever, diarrhea, hemorrhage, circulatory problems


toxins released into surrounding environment as soon as the toxin is made, some of the most powerful toxins known, damages cell membrane and lysis of cell, only need small amounts of toxin to cause damage

Host Factors of Diseases (Possible Discussion Question)

Delicate balance between bost's various defence mechanisms and the virulence factors of the MO
If the host's defense mechanisms are good, there is less chance of getting a disease
If the MO virulent factors are higher than host's defense mechanisms, good chance of getting a disease

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