Infection Flashcards
Symbiosis
When both the host and the associated organism benefit from the union.
Example: In our colons, we carry large number of bacteria that synthesize vit K from contents of large bowel; we reabsorb the vitK that bacteria produce and we give food to the bacteria.
Commensalism
When an organism merely hitches a ride and shares the host’s food; the organism doesn’t usually help or hinder the host.
Saprophytic
Live off dead and degenerate material; vitamin K producing bacteria are symbiotic and saprophytic; because they help the host while living off degenerating material in the colon.
Parasitism
True parasites interfere with the host’s integrity and function; the more they interfere with the host the more pathogenic the parasite; pathogenic=disease causing, virulence=quality of being poisonous.
Host Resistance
An organisms ability to fight disease:
- some hosts are better able to deal with infectious agents
- Certain species of animals can harbor organisms that would be dangerous to human
- certain pops of humans can tolerate diseases that can devastate naive pops that have never seen the disease
- whether the host is will nourished or not
- whether the host is young or old
- whether the host has a normally active, sub-active, or hyperactive immune system
Mechanical Barrier to Infection
The skin and mucous membranes of orifices block penetration of organisms into the body.
Secretions-Barriers to Infection
Tears, saliva, and urine protect by washing microbes away and diluting the concentration of organisms present. Mucus produced in the respiratory tract and bowel traps organisms.
Factors in bodily secretions such as enzymes and antibodies are inhibitory or directly toxic to microorganisms (lysozyme in tears).
Epithelial Barrier to Infection
in addition to being a mechanical barrier, also help to prevent infection by process of exfoliation; old, dead, and/or dying cells fall off epithelium and are replaced by new fresh underlying cells-organisms are carried away with the older cells
Example: cilia in respiratory tract
Chemical Barrier to Infection
The acidity, pH, of the stomach and skin are bactericidal
Normal microbial flora Barrier to Infection
Normal microorganisms have evolved along with the host and are well suited to inhabit their ecological sites.
They compete successfully for nutrients against other types of microorganisms that might be pathogenic-they defeat the bad bugs!
If normal flora get into sites they don’t originally habitat, they can cause disease.
Living tissue responds to injury:
- limit spread of the agent
- destroy agent
- prepare for repair of injured region
WBC respond
Granule containing leukocytes: neutrophils, eosinophils, basophils (cytoplasmic colors take up colors with standard stains)
Non-granular leukocytes: lymphocytes and monocytes
Phagocytotic cells: neutrophils, eosinophils, monocytes
Humoral Immunity: antibody (immunoglobulin) production; they are made in response to certain compounds called antigens; once an antibody is bound to an antigen, cellular and chemical defenses are called into play to eliminate the source of the antigenic stimulus.
Cell-Mediated Immunity: T lymphocytes mediate this response; produce killer cells that attack, secrete substances that can call in and turn on macrophages, help regulate antibody production by interacting with B cells, control the immune system so that it does not get out of hand.
Organism Factors in Infectious Disease
An organism may have more than one mechanism to produce disease:
Toxins; may be made by organism or be liberated when organism is destroyed by the body’s efforts to get rid of it
Some parasites are not toxic at all; the host’s reaction to the invading agent may be very dramatic and normal structure that get in the way of host’s response end up getting damaged.
Properties of Organisms
PARASITES CAN ADAPT TO HOST DEFENSES
Variable Pathogenicity: certain parasites are always pathogenic; but some only cause disease if they get into the wrong place or the host immune system is impaired-opportunistic or facultative pathogens.
Example: fungus Candida Albicans-Normally present in mouth, GI, vagina, but in impaired host it may grow and case serious damage or death.
Carrier State: when someone harbors a pathogenic organism and does not show disease; but can pass it on to someone else
Spreading Factors: some organisms can produce these, which help break down tissues and allow them to extend region of infection.
Other microbes have evolved methods to get around protective methods of the host; make enzymes that kill WBC before they can attack bacteria OR have developed specialized coatings that give protection against chemical and cellular assaults by host.
Reproduction=genetic variation (reproduction VERY fast in microbes)
Some worms can change antigens on their surface evading immune detection altogether.
Transmission of Infectious Disease
Most get in by way of natural passages (mouth, airways, genitourinary tract); can also get in through way of skin.
Direct Physical Contact
May transfer organisms from one host to another; sexual contact can transfer infectious agents from one partner to another, microorganisms might be present in secretion exchanged.
Indirect Physical Contact
Passage of infectious material by means of articles like drinking glasses, utensils, clothing.
Implies that organism must be able to survive outside of body.
Fomites (usually small) are capable of harboring and transmitting agents of disease (article of clothing to a droplet produced by a sneeze).
THIRD PARTY INVOLVED
Airborne Infection
Many bacterial and viral infections are spread by dust or droplets in the air. 20,000 droplets during sneezing projecting 10-15 ft
Food, water, or soil-borne infection
contaminated food, diseases of sanitation; GI disease.
Insect-borne infection
Insects are major carrier of infection (plague, yellow fever, and malaria-1-2 million deaths/year).
FIVE FS OF INFECTION SPREAD
- Fomites (TB-coughing)
- Food (food poisoning)
- Fingers (wash hands)
- Flies (Titzi fly-agent of African Sleeping Sickness)
- Feces (Tapeworm)
General Characteristics of Bacteria
Prokaryotes
Different than eukaryotic cells:
smaller size
absence of nucleus and many other organelles
ribosomes smaller
cell wall surrounding cell membrane, similar to cell walls of common plants
may additionally have a capsule around the cell wall
no defined mitochondria
They exist as individual cells-complete organisms
Mucoid capsule may allow pathogenicity because it can make phagocytosis by other cells difficult
Cell walls and capsules confer immunologic specificity to bacteria of a given type.
Shape Classification
coccal-spheroidal (round)
bacillary-cylindrical
spirochetes-spiral shaped
Staining reactions
Gram Stain reactions-used to see bacteria shapes Gram positive (keep purple color) Gram negative (lose purple, are now red)-most are negative, a lot of endogenous bacteria Acid-fast Stain Reaction (important for mycobacterial infections).
Cultural Features
Necessary to grow organisms in large numbers in culture to identify them.
They acquire adequate food, temp, amount of moisture, oxygen.
Different types of bacteria have different requirements for these elements- can be identifies or classified by their needs.
Colony formation in culture: when grow on artificial media, bacteria tend to form characteristic groups (colonies).
