Definition of pathogen
agent causing disease or illness to its host
-> organism/infectious particle capable of producing a disease in another organism
Definition of opportunistic pathogen
infectious microorganism normally commensal or doesn’t harm its host but can cause disease when the host’s resistance is low
Definition of pathobiont
commensal (or symbiont) able to promote pathology only when specific genetic or environmental conditions are altered in host
-> better to think about “pathogenic potential”
Definition of commensal
one organism derives food or other benefits from another organism without hurting/helping it
-> in humans: more mutualistic relationship
Definition of symbiont
an organism in a symbiotic relationship
-> mutual benefit
Name the ‘father of modern microbiology’
Robert Koch
Briefly describe Koch’s studies on Anthrax (B. anthracis)
Bacillus anthracis
mostly found in sheep and cattle
=> cause or result of disease unknown at this time
all infected animals carried bacillus in their blood (through blood smears)
-> chain of transmission & re-infection from infected to healthy individual possible
=> pure bacterium cultures can infect healthy animals through re-inoculation
Name 2 other bacterial pathogens Koch worked on
tubercolosis (1882)
cholera (1883)
List and describe the 4 Koch’s postulates
Understand the limitations of each of these postulates
microorganism only found in diseased animals, not found in healthy animals
-> only fraction of pathogenic organisms produce disease besides found in healthy individuals
=> different immune system
microorganism extracted and isolated from diseased and subsequently grown in culture
=> right medium needed to grow culture (many not grow in nutrient medium culture)
microorganism must cause disease when introduced to healthy experimental animals
-> won’t introduce disease in all healthy individuals
=> depending on many factors (indivudals immune system, health, etc.)
=> sometimes species specific -> not reproducable on other species
microorganism extracted from experimental diseased animal and demonstrated to be the same microorganism that was orginally isolated from the first diseased animal
-> initial infection with (long-term) symptoms and culture/infection long gone
List and describe the 3 molecular Koch’s postulates and how they relate to ETEC and EHEC (when compared to non-pathogenic E. coli)
phenotype associated only with pathogenic strains of a species
inactivation of suspected gene(s) associated with pathogenicity should result in measurable loss of pathogenicity
-> not right model available, knockout not possible
reversion of inactive gene(s) should restore disease phenotype
=> Eschericha coli genereally harmless in human intestines
<=> ETEC and EHEC pathogenic strains of E. coli
Know the different terms used to describe commensal and pathogenic bacteria (plus brief description of what each term means)
pathogen
opportunistic pathogen
pathobiont
commensal
symbiont
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