Bacteria and Host interactions Flashcards
Mutualism or Symbiosis
Both microbes and thier host benefit from the interaction
Commensalism
Microbes benefit and the host is not affected.
The microb involved in commensalism is called a commensal
Normal Flora
Microbes that establish a more or less permanent residence but do not produce disease under normal conditions,
- Protective Functions:
- Prevent the entry and establishment (overgrowth) of other bacteria, including pathogenic bacteria
Parasitism
Microbes benefit from the host while harming the host.
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Parasite
- an organism that benefits at the expence of another organism.
- Harm ranges from no recognizable damage to overt damage even death.
Pathogen
any disease-causing microorganism
specifically used to refer to bacterial, fungus, and viral agents of disease.
Saprophyte
A bacterium that is in the environment and does not cause any disease
Molecular Postulates
Koch’s postulates are now supplemented and often supplanted by certain molecular criteria, which use percise genetic techniques to determine the pathogenicity of microorganisms
- THe virulence factor gene of its product should be found in pathogenic strains but not in the nonpathogenic strains of the suspected organism
- The genes for virulence must be expressed during the disease process
- Introduction of a virulence gene should change nonpathogenic stains to a pathogenic strain, whereas disrupting the function of the virulence gene should reduce the virulence of the organism
- Antibodies or immune cells for the virulence gene products should be protective.
Etilogy
Cause of disease
Koch’s Postulates
Robert Koch:
- was the first one to demonstrate taht bacteria cause disease, by studying anthrax
Koch’s Postulates:
- The pathogen must be present in every case of the disease
- The pathogen must be isolated from the diseased and grown in pure culture.
- The pathogen from the pure culture must cause disease when it is inoculated into a healthy, susceptible animal
- The pathogen must then be recovered from the inoculated animal
Exceptions:
- Some bacteria cannot be cultured in laboratory media
- Some infectious diseases are saused by different pathogens, which makes it difficult to identify which particular organism is involved
- Some infectious diseases are acaused by mixed Infections (polymicrobial infections)
- Some pathogens cause several disease conditions
Pathogenesis
The process by which the etiologic agent causes the disease
Pathogenicicty
Potential of an organism to cause disease.
Is shaped by the genetic makeup of the pathogen
Viulence
Relative pathogenicicty or a measure of the degree or severity of disease.
Describes attributes of the pathogen that promote pathogenicity.
Can be:
- Highly virulent
- Moderately virulent
- Avirulent
Virulence Factors
Substances contained in or secreted by the pathogen that confer virulence to the microorganism.
Include cell surface proteinds, cell surgace carbohydrates, toxins, hydrolytic enzymes
Invasiveness
Ability to enter, survive, multiply, and spread within host tissues
Primary Pathogen
A microbe that can initiate disease on its own
Secondary pathogen
A microbe that invades or extablishes itself in host tissues due to the presence of a primary invader.
Opportunistic Pathogen
A microbe, often part of the normal flora, that is normally not pathogenic, but can cause disease upon lowered host resistance or when intorduced into a different location.
Extracellular Pathogen
Grows and multiplies in the space and fluids surroinding the cells.
In the laboratory, they are grown in conventional culture bacteriological media.
Majority of pathogens
Intracellular Pathogen
Grows and multiplies inside cells.
Internalized by both phagocytic and nonphagocytic cells
Facultatively Intracellular Pathogens
Have the ability to grow and multiply both inside and outside the cell.
In the laboratory, they can be cultivated in culture media in the absence of living cells
Obligately Intracellular Pathogen
Grows and multiplies only inside the cells.
In the laboratory, they cannot be cultivated in conventional bacteriological media.
Lack the ability to grow independently, and can be grown in cell culture.
Mechanism of Intracellular Survival
Nonphagocytic Cell uptake:
- Ability of the bacteria to enter nonphagocytic cell requires specific uptake mechanisms.
- Essentially three options to avoid being killed once taken into the cell:
- Escape the phagosome:
- produces hemolysin to break out of the phagolysosome. Escape the effects of the lysosomal enzymes and grow in the cytoplasm
- Prevent Fusion of Phagosome and lysosome:
- Prevent fusion by secreting proteins that interfere with the cell-signaling pathways taht cause phagosome-lysosome fusion
- Survive the harsh environment:
- Some pathogens are able to survive the harsh environments of the phagolysosome.
- Escape the phagosome:
Infection
the invasion or colonization of the body by a pathogenic organism.
Presence of a particular organism in a part of the body where it is not normally found
disease
occurs when an infection results in any change from a state of health.
Infectious Disease
disease caused by a microorganism
Contagious disease
infectious disease that is readily spread from an infected animal to another animal
Primary Infection
Infection in a previously healthy host
Secondary infection
occurs along with or immediately following another infection
Exogenous infection
infection caused by bacteria that originate from outside the animal
Endogenous infection
infection that originates from within the animal
Latent infection
infection in which the causative agent remains inactive for a period of time but then becomes active to cause an infection
Zoonotic infection (zoonosis)
infection or a disease, primarily of animals, that can be transmitted to humans.
Nosocomial infection
infection that is acquired in a hospital.
Major problem in human medicine
Caused by a variety of organisms, including bacteria, fungi, viruses, parasites, and other agents.
Sporadic Disease
disease that only occurs occasionally
Endemic disease
disease that is constantly present in a population
Epidemic disease
disease that occurs in a relatively short period of time in a large number of animals in a population or herd
Pandemic Disease
Endemic disease that occurs worldwide
Acute infection
the symptoms have a rapid onset and are usually severe and last only for a short time
Peracute disease
A higher degree of acute disease
Chronic Disease
infections develop more slowly, are less severe and last longer (months to years)
Incubation period
interval between the entry and the first symptoms or signs of illness
Mucous Membranes
Many bacteria gain access by penetrating the mucous membrane lining the respiratory, gastrointestinal, and genitourinary tracts and the conjunctiva of the eye.
- Adherence
- Adherence:
- after entering the body, bacteria attache to the cells to facilitate colonization and infection.
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adhesion:
- process by which bacteria attach to cells
Toxins
Chemicals contianed in or produced by pathogens that damage tissues or trigger host immune responses that cause damage.
Often the primary factro contributing to toxigenicity
Cell membrane Damage
Damage to the cell membrane causes leakage of cell contents resulting lysis and death of cells.
One type of membrane damaging tixins Pore Forming toxin.
Which inserts directly into the cytoplasmic membrane to form channels.
Hemolysins
Membrane disrupting toxins that lyse red blood cells.
alpha toxin of S. aureus
Leukotoxin
Membrane disrupting toxins taht lyse and kill phagocytes or white blood cells.
A-B toxins
Have two subunits, designated A and B, both of which are polypetides.
The A part is the active component whit biological activity, and B part binds to the cell to allow transfer of A into the cell to exert its biological activity.
A subunit possesses enzymatic activity that is specific for each toxin.
A-B toxin:
Shiga Toxin
Toxins are produced by Shigella dysenteria and enterohemorrhagic E. coli (EHEC)
The most common EHEC is a foodborne pathogen taht causes bloody diarrhea in humans. Cattle are major reservoirs of this organism.
Another serotype of EHEC causes a disease in pigs called edema disease
AB toxins with 5 B subunits and 1 A subunit, that bind to a glycolipid receptor, globotriaaosylceramide (GB3), at the surface of the epithelial or endothelial cells, permitting the toxin to be internalized by receptor-mediated endocytosis.
A-B Toxins
Enterotoxins
Affect enterocytes lining the small intestine, generally causing massive secretion of fluid into the lumen of the intestine, leading to diarrhea.
AB toxins and exert their biological activity by stimulating cGMP and cAMP.
Affect ion balance in enterocytes causing secretion of electrolytes and water into the lumen.
A-B Toxins:
Neurotoxins
Two major neutotoxins are tetanus and botulinum toxin
Both are AB toxins that block release of neurotransmitters involved in muscle activity.
Botulinum Toxin:
- is internalized at the neuromuscular junction, blocking the release of acetyl choline, and inhibits muscle contration.
Tetanus Toxin:
- From the site of infection is transported through the motor neurons to the spinal cord, where it binds specifically to ganglioside lipids at the inhibitory interneurons.
Endotoxins
Also called Lipopolysaccharides.
Part of the outer membrane of Gram - bacteria composed of lipopolysaccharides, phospholipids, and proteins.
Released when bacterial cells die naturally or digested by the phagocytes
Alarm Reaction
At low concentrations of endotoxins
Fever, activation of complement. activationof macrophages, and stimulation of B-lymphocytes.
At high concentrations endotoxins cause shock and even death
Shock
In large doses, endotoxins can cause a condition of loss in blood pressure.
Phagocytosis of Gram - bacteria causes phagocytes to secrete a polypeptide called Tumer Necrosis Factor (TNF). TNF binds to many tissues and alters their metabolism.
TNF can cause damage to capillaries, causing their permeability to increase and loose large amounts of fluids, resulting in loss of blood pressure.
Comparison of Bacterial Exotoxins and Endotoxins
Know the following table very well
