Why Study Pathogens?

treatment rehydration, profuse rice water diarrhea, sunken jaws, eyes, shock

Vibrio cholerae
Gram-negative, marine species
comma, motile, facultative aerobe, mesophile
2 circular chromosomes 4Mb
water borne disease
Cholera toxin (exotoxin), Type IV pili (toxin coregulated pilus TCP)

Cornebacterium diphtheriae
gram-positive, soil organism
bacilli, non motile, aerobic, mesophile
one circular chromosome 2.5 Mb
air borne disease
Diphtheria toxin

white large membranes form

constant major muscle spasms, immunization very effective

clostridium tetani
Gram-positive, soil species, intestine animals
bacilli, non motile, anaerobe, mesophile, spores
one circular chromosome 2.8 Mb
wound infection
tetanus toxin exotoxin Neurotoxin

mycobacterium leprae
gram positive, host associated
bacilli, non motile, aerobic, mesophile
one chromosome 3.3 Mb
airborne droplets
symptoms result from host immune response

extracellular pathogens
grow outside cells in blood, tissue fluids

intracellular pathogens
grow and multiply within cells

faculatative intracellular pathogens
grow within or outside cells

obligate intracellular pathogens
only grow within cells

extracellular pathogens
Clostridium botulinum
Clostridium tetani
Corynebacterium diphtheriae
Escherichia coli pathovars
Vibrio cholerae
Borrelia burgdorferii
Neisseria gonorrhoeae

intracellular pathogens
Chlamydia trachomatis
Escherichia coli pathovars
Legionella pneumophila
Mycobacterium leprae
Rickettsia rickettsii
Treponema pallidum
Salmonella enterica
Yersinia pestis

larger organism that supports the survival and growth of a smaller organism

live on or within a host organism and are metabolically dependent on the host; are any organism that cause disease

a parasite growing and multiplying within/on host; may or may not result in overt infectious disease

any parasitic organism causing infectious disease

primary pathogen
causes disease by direct interaction with healthy host

opportunistic pathogen
may be part of normal flora and causes disease when it has gained access to other tissue sites or host is immunocompromised

ability of parasite/pathogen to cause disease

humans, animals

infections passed from animal to human

water, food, soil

natural environmental location in which the pathogen normally resides

objective changes in body

subjective changes experienced by patient

disease syndrome
set of characteristic signs and sympotoms

incubation period
period after pathogen entry, before signs & symptoms

prodromal stage
onset of signs and symptoms

period of illness (acute and decline periods
acute period disease is most severe, decline period signs and symptoms begin to disappear


degree or intensity of pathogenicity

virulence factors
determine the degree to which the pathogen causes damage, invasion, infectivity

infectious dose 50
number of organisms (CFUs) that will infect 50% of hosts in a specified time

lethal dose 50
dose that kills 50% of experimental animals within a specified period

a person who is infected with an organism but shows no evidence of disease

acute infection
implies a ‘short-lived’ infection, a few days

chronic infection
refers to a ‘long-standing’ condition, months to years

latent infection
refers to a persistent infection with possible intermittent shedding

local infection
gastrointestinal tract

systemic infection
multiple systems/organs

transient bacteria in blood

growth of bacteria in blood

primary infection
weakens immune system and allows for secondary infection

secondary infection
primary infection weakens immune system allows for _________

subclinical infection
pathogen infection but no overt or acute symptoms

AB extotoxins
toxin composed of two subunits

A subunit
subunit responsible for toxic effect

B subunit
subunit that binds to specific target cell

toxin that is part of the bacteria, ex. Gram – Lipopolysaccharide in cell wall

molecular mimicry
decorating cell surface with host-like molecules known as molecular mimicry

binary fission
how bacteria reproduce, clonal population structure

horizontal gene transfer
bacterial sex

congenital infectious
babies born with an infectious disease are said to have ________