Host-Microbe Relationships Flashcards
Define symbiosis
a close association and interaction of 2 dissimilar organisms living together
Define normal microbiota
microorganisms which are normally AND consistently found in or on the body in the absence of disease
-microbes vary in body regions and may cause infection if they are introduced from one body region to another
Commensalism
association between organisms in which one is benefitted and the other is neither benefitted or harmed
Mutalism
both organisms benefit from an association
Opportunism
disease traits of the resident microorganisms/flora that are only demonstrated when the host-microbe relationship is altered
Parasitism
association between organisms in which one is benefitted and the other is harmed
Vector
a carrier of microbe from one host to another
ie insects to humans, humans to humans, or inanimate objects to humans
Infectious disease
the growth and spread of a pathogen in or on a host resulting in injury to tissue
Pathogen
a microbe capable of causing dz
Virulence
degree of pathogenicity
Infectivity
how easily a microbe survives normal host defenses
Severity
damage a pathogen causes in its host
What are modes of transmission
- Direct contact with skin or mucous membranes
- Inhalation
- Ingestion
- Parenteral= direct contamination of blood
What are the 3 ways a microbe can attach to tissue to establish an infection
- Surface chemicals= chemicals that dissolve the covering of cells and aid in chemical attachment
- Fimbrae= thread like projections of the bacterial cell that attach to specific sites on specific tissues
- Binding to surface molecule= a specific molecule on the microbe binds to a specific surface receptor on the tissue
What are adhesive matrix molecules
biofilms that provide bacteria protection for bacteria in harsh human conditions
What are Quorum-sensing regulators
various chemicals that restrain the dz causing actions of the microbe until sufficient numbers of microbes are present then they switch on the dz causing action all at once
Why is portal of entry important for virulence
the microbe must enter the correct portion of the body to causes dz
What are common antiphagocytic factors used by microbes
- Capsule=slippery
- Leucocidins= chemicals that destory WBCs
- Coagulase= causes clot to form around microbes
- M protein of Group A strep= antiphagocytic protein
- Protein A of Staph= binds IgG and block complement activation
- Generally resistant to killing by phagocyte= ie bacteria can live inside phagocyte
What are Invasive Enzymes
factors that promote the invasion and spread of a pathogen
What are common examples of invasive enzymes
- Collagenase= destroys collagen thus decreasing tissue integrity
- Lecthinase= breakdowns lecthin portions of host cell membrane thus causing destruction of membrane
- Hyaluronidase= breaks down hyaluronic acid portions of host cell membrane thus causing destruction of membrane
- Fibrinolysin and streptokinase= breaks clots thus preveting isolation of infection
- Hemolysins= dissolves RBC membranes
- lipase
- Proteases
- Superantigens
What are exotoxins
Proteins excreted from the cell that causes specific (tissues affected are defined) and widespread biologic effects on the body
-highly potent and cause good release of antibody release
example=tetanus, cholera, diptheria
True or False many exotoxins are dimeric
True, they contain A&B subunits that facilitate entry into the cell
True or False superantigens are a type of exotoxins
True
What does the diphtheria exotoxin cause
interferes w/ protein production of bronchial epithelial cells causing production of mucous and blockage of respiratory tract
What is Lipid A
Endotoxin that is a component of the lipopolysaccharide in GRAM NEGATIVE CELL WALLS ONLY which when released once the cell dies causes the production and release of scute phase cytokines
- not very potent, needs high levels to cause effects
- does not elicit a good antibody response
How do bacteria gain Abx resistance
- Mutated genes ( 1 in 10 billion cell reproductions)
- Transfer of plasmid encoded resistance genes (exotoxins, abx resistance, and invasive enzymes)
- Lysogenic virus
What is beta-lacatmase
- a bacterial enzyme that inactivates beta lactam Abx by breaking the beta lactam ring
- gene is usually carried on plasmid of enterobacterum
What is extended spectrum beta lactamase
a bacterial enzyme that affects a larger group of Abx that are typically not affected by typical beta-lactamase
Describe Methicillin Resistant Staphylococcus Aureus (MRSA)
- staphylococcus aureus that is resistant to methicillin and all beta lactams
- resistance caused by mutated mecA genes which codes for a low affinity penicillin binding protein (PBP)
Describe Carbapenem Resistant Enterobacteriaceae (CRE)
- Enterobacteriaceae that have mutated genes for outer membrane porins and PBP resulting in loss of Abx diffusion into the periplasm and cross linking activity of PBP
- form of beta-lactamase
- carried on plasmid
How do humans resist infection
- physical and mechanical barriers (skin, mucus, normal flora…)
- chemical barriers (stomach acid, bile, lysozyme, interferon…)
- phagocytosis
- Inflammation
- cell mediated immunity
- complement and antibodies
What is the typical number of days on which shedding occurs in bacteria
1 or 2 days through resolution of illness but some shed even a couple of days after resolution
What is the typical number of days on which shedding occurs in viruses
1 to 7 days until fever resolves, some viruses shed prior to showing signs/symptoms
Define infectious dose
dose of microbe needed to causes infection
What does excessive shedding over infectious dose suggest
The microbe is easier to contract the infection
What is the coronavirus timeline
Incubation time=~5 days
Shedding= 1 or 2 days before symptoms (day 3 or 4 from entry), shedding increase through about day 9 or 10
Define R naught
The reproductive number and it represents the number of persons to whom infection is passed from each infected person
What is the R naught for COVID
1.5-2.5
What are the effects of quarantine in a pandemic
- reduces # of cases in the eary period so healthcare systems are not overloaded
- reduces the # of cases by reducing number of cases during the long term by reducing the # of microbe in the community
Define herd immunity
term that describes when a high percentage of a population has immunity and few new cases of a specific dz develop
