Later Encounters EXogenous: encountered in environment Endogenous: encountered in or on body Organisms present on skin can cause disease when they go into deeper tissues BIOL 533 Lecture One
Lecture One BIOL 533 7 Later Encounters • Exogenous: encountered in environment • Endogenous: encountered in or on body – Organisms present on skin can cause disease when they go into deeper tissues
Later Encounters Example Staphylococcus aureus enters cut and forms boil In this case encounter took place long before disease (at time skin was colonized) Encounter is not always sharply demarcated BIOL 533 Lecture one
Lecture One BIOL 533 8 Later Encounters • Example: – Staphylococcus aureus enters cut and forms boil – In this case, encounter took place long before disease (at time skin was colonized) • Encounter is not always sharply demarcated
Normal flora What constitutes normal flora? Some people possess StreptocoCCus pyogenes in their throat for long periods, but rarely contract disease Opportunistic pathogen existence(carrier state) 95% of people never have this bacterium, and when they do, they get sick BIOL 533 Lecture One
Lecture One BIOL 533 9 Normal Flora • What constitutes normal flora? – Some people possess Streptococcus pyogenes in their throat for long periods, but rarely contract disease • Opportunistic pathogen existence (carrier state) – 95% of people never have this bacterium, and when they do, they get sick
Normal flora defined Constitutes normal fora if definition is any organism present that is not causing disease Not normal fora if used to mean organisms present in majority of population BIOL 533 10 Lecture One
Lecture One BIOL 533 10 Normal Flora Defined • Constitutes normal flora if definition is “any organism present that is not causing disease” • Not normal flora if used to mean organisms present in majority of population
Host-Parasite Interaction Exposure to virulent agents does not always lead to disease Typhus and Black Plague epidemics only half of population became sick, even hough most likely exposed BIOL 533 11 Lecture one
Lecture One BIOL 533 11 Host-Parasite Interaction • Exposure to virulent agents does not always lead to disease – Typhus and Black Plague epidemics: only half of population became sick, even though most likely exposed