bact/host interactions Flashcards
what is mutualism or symbiosis?
bacteria and host are benefited
what is commensalism
bacteria are benefited and the host is ‘unaffected’
what is parasitism
bacteria are benefited and the host is harmed
what is another name fore normal flora?
commensals
where are commensals located?
skin and mucous membranes
what is bacterial antagonism
where bacteria compete for attachment, nutrients and produce substances that inhibit
what are probiotics
beneficial bacteria
the use of probiotics enables what ?
competitive exclusion
what is a pathogen
any disease-causing microorganism
what is etiology?
the cause of the disease
what is pathogenesis
the process of disease development
what is pathogenicity
capacity of an organism to cause the disease
what is virulence
relative pathogenicity
what is attenuation
reduction in virulence
what is invasiveness
ability to enter, establish and spread in the body
what are Koch’s (4) postulates
- pathogen must be present in every case of the disease
- pathogen must be isolated from the infected host and grown in pure culture
- pathogen must cause the disease when inoculated into another host
- pathogen must be recovered from the inoculated host
are there exceptions to Koch’s postulates?
yes
-e.g. more than one bacteria cause one disease (V/v), polymicrobial infections, etc
what is an opportunistic pathogen?
causes disease only when conditions are favorable
what is a primary pathogen?
causes disease on its own
what is a secondary pathogen?
follows a primary pathogen, on its own it may or may not cause the disease
what is an extracellular pathogen?
grows and multiplies in the space and fluid surrounding the cells
what are intracellular pathogens
grows and multiplies inside the cells
what are the two types of intracellular pathogens
facultative and obligate
what are facultative intracellular pathogens?
grows and multiplies inside cells and outside cells
-can be cultured in bacteriological media
what are obligate intracellular pathogens
grows and multiplies only inside cells
-can be cultured in the lab in tissue culture media
define infection
invasion or colonization by a pathogen
-may or may not result in disease
define disease
change from a state of health
what is an infectious disease?
caused by a microorganism
what is a contagious disease?
spread by contact
what is a primary infection?
infection in a previously healthy host
what is a secondary infection?
occurs along with or immediately following an infection
what is an exogenous infection?
bacteria originate from outside the animal
what is an endogenous infection?
bacteria originate from within the animal
what is a latent infection?
pathogen remains inactive till the conditions become favorable to cause an infection
what is a zoonotic infection?
an animal infection or disease that is transmitted to humans
what is a nosocomial infection
an infection acquired in a hospital
define sporadic disease
occurs occasionally
define endemic disease
consistently present in a population
define epidemic disease
occurs in a large number of individuals in a population
define pandemic disease
occurs worldwide
define acute duration of disease
rapid onset, usually severe, and last for a short period of time
define peracute duration of disease
higher degree of acute disease
define chronic duration of disease
slow onset, less severe, and lasts longer
define subacute or subclinical duration of disease
mild with no overt signs or symptoms
define localized in terms of extent of host involvment
confined to a relatively small area
define generalized or systemic in terms of extent of host involvment
spreads throughout the body, spread is because bacteria enter the lymph or blood circulation
define bacteremia in terms of extent of host involvment
bacteria circulating in the blood
define septicemia in terms of extent of host involvment
bacteria multiplying in the blood (sepsis)
define toxemia in terms of extent of host involvment
toxin is circulating in the blood
define focal infection in terms of extent of host involvment
bacteria from a local infection enter lymph or blood to set up local infection in other parts of the body
define incubation period
interval between the entry and the appearance of first symptoms or signs (days to weeks to months)
define illness
signs and symptoms are evident
define symptoms
effects of the disease experienced by the patient (pain, nausea, etc)
define signs
effects of the disease observed by examining the patient (fever, swelling, etc)
**measurable
define convalescence
period of recovery
what are predisposing factors?
factors that make the animal more susceptible to infection
-nutrition, age, stress, etc
define adhesion
process of adherence
define adhesins or ligands
structures on the bacteria, generally proteins, that mediate adhesion
-found on flagella, fimbrae, outer membrane, capsule
define receptors
structures, generally glycoproteins, on animal calls that mediate attachment
what is colonization?
growth after attachment
what is invasion?
internal spread beyond the site of entry
what is a prerequisite for infection?
colonization
what is quorum sensing?
cell to cell communication to control cell density
-mediated by secretion of small molecules
what are virulence factors?
structures or substances produced by bacterial that help establish the pathogen to cause the disease
-attachment factors, enzymes, toxins
what do hyaluronidases do?
breaks don hylauronic acid, the intercellular cement
what do coagulases do?
causes fibrin formation to protect bacteria from host’s defense
what do strptokinases do?
dissolves fibrin (blood) clot formed to isolate pathogens
what is toxigenicity?
capacity of bacteria to produce toxin
what type of bacteria produce exotoxins?
both gram positive and gram negative bacteria
what type of bacteria product endotoxins?
only gram negative
what are the characteristics of exotoxins?
proteins and many have enzyme activity
what are antitoxins?
antibodies against toxins
what are toxoids?
inactivated toxins
what are the 5 mechanisms of action of exotoxins?
- cell membrane disruption
- protein synthesis inhibitor
- second messenger pathway disruption
- superantigens
- proteases
what do hemolysins do?
lyse RBC
what do leukotoxins do?
lyse WBC
what do cytotoxins do?
lyse any cell
how is hemolytic activity determined?
by streaking organisms on to blood agar
what are two cytotoxic protein synthesis inhibitors?
shiga toxins
diphtheria toxins
what do superantigens do?
activate the immune system and provoke a very intense immune response
- stimulate proliferation of T cells
- release cytokines
two examples of bacteria that use toxins as proteases
- tetanus toxin from clostridium tetani
- botulinum toxin from clostridium botulinum
what type of bacteria produce shiga toxins?
Shigella dysenteriae and Shiga toxin-producing E. coli (STEC)
how do shiga toxins work?
inhibit protein synthesis
what animal is a major reservoir for STEC?
cattle
what do enterotoxins do?
affect enterocytes causing massive secretion of fluids (diarrhea)
what are two important animal pathogens that produce enterotoxins?
E. Coli and Salmonella enterica
what do neurotoxins do?
block the release of neurotransmitters
what are endotoxins?
lipopolysaccharides
-part of the outer membrane of gram negative bacteria
what is lipid A responsible for in endotoxins?
responsible for biological activity
what is the polysaccharide responsible for in endotoxins?
responsible for antigenicity
what do endotoxins do in the bod?
- fever, inflammation, blood, coagulation, hemorrhage, and shock
- cause release of cytokines in high concentrations
what are teh three major effects of endotoxins?
- fever
- intravascular coagulation
- shock
what is disseminated intravascular coagulation (DIC)
- activation of blood-clotting proteins, causes formation of blood clots
- clots block capillary blood flow resulting in decreased blood supply and tissue necrosis
what happens in endotoxic shock?
- loss of blood pressure
- release of TNF
- TNF damages capillaries causing increased permeability and loss of fluids
what are pathogenicity islands?
a cluster of multiple genes that code for virulence factors
-absent in nonpathogenic bacteria
