Lec3 Flashcards
is the M.O that can cause a disease.
Pathogen
is the M.O that take the opportunity of a reduced host defense to cause a disease.
Opportunistic pathogen
is a quantitative measure of pathogenicity
Virulence
which is the number of M.O cells needed to kill half of the hosts.
LD50
which is the number of M.O cells needed to cause infection in half of the hosts.
ID50
Infection dose of shigella
100 cells
Infectious dose of salmonella
100,000 cells
Why the LD50 and ID50 values varies among bacteria?
1: Presence of pili allow them adhering the mucous
membranes easily.
2: Presence of a capsule protect them from phagocytosis.
3: Ability to survive host defenses such as stomach acid.
4: Ability to produce exotoxins or endotoxins.
5: Ability to produce lytic enzymes.
can grow within cells, outside cells, or on bacteriologic media.
Facultative parasites
Chlamydia and Rickettsia, can grow only within host cells.
Obligate intracellular parasites
conditions required for infection
- The correct portal of entry.
- High number of microbial cells.
- The virulence of M.O.
- Weak immune system increases the chance of infection.
Bacteria cause diseases by two major mechanisms:
- Invasion and inflammation.
- Toxin production
Stages of bacterial pathogenesis
- Transmission from an external source into the portal of
entry. - Overcome the primary host defenses such as skin, mucous, saliva, stomach acid.
- Adherence to mucous membranes (by pili or capsule).
4.Colonization of the site of adherence (invasion and
inflammation). - Toxin and enzyme production.
- Appearance of symptoms.
- Host responses during the previous steps.
- Progression or resolution of the disease.
mode of transmission:
Human to human
Nonhuman to human
Human to human transmission
- Direct contact (sex, hand shaking).
- Indirect contact (Fecal—oral)
- Transplacental (Bacteria cross the placenta and infect the fetus).
- Blood-borne (through blood transfusion).
Nonhuman to human transmission
- Soil source
- Water source
- Fomite source
- Animal source
Transmission of microbes drom=mother=tomofispring: via
placenta, birth ‘canal, and breast milk called
vertical transmission.
by contrast, include person-to-person transmission.
Horizontal transmission
mediate the attachment to the urinary tract epithelium.
pili of E. coli
mediate the attachment to the heart valves endothelium.
glycocalyx of viridans streptococci
play an important role in the formation of dental plaque.
Biofilms
strains have surface proteins called
curli
protects bacteria from phagocytosis by walling off the infected area and coating the organisms.
Clot
destroy both neutrophilic leukocytes and macrophages.
Leukocidins
M protein of St pyogenes
antiphagocytic.
binds to IgG and prevents the activation of complement.
Protein A of Staph. aureus
Pyogenic (pus-producing) inflammation
where neutrophils are the predominant cells (most cells)
Granulomatous inflammation
where macrophages and T cells predominate.
Obligate intracellular parasites
(Chlamydia and Rickettsia)
Escape from the phagosome into the cytoplasm, where there are no degradative enzymes.
Listeria
specific bacterial surface proteins called
invasins or adhesins
are virulence factors that inhibit phagocytosis and cytokine production.
“Yops” (Yersinia outer-membrane proteins)
is a “master controller” of many virulence factors in several pathogens.
DNA adenine methylase (Dam)
inability of hydrophilic drugs to enter the lipid-rich brain parenchyma, whereas lipophilic (lipid-soluble) drugs enter well.
“blood-brain barrier”
Endotoxin source
Cell wall of G-ve bacteria
Exotoxins toxicity
High
