Pathogenesis Of Microbial Infections Flashcards
Definition of symbiosis
Close and often long term interaction between 2 biological species
Definition of commensalism
1 organism benefits and the other derives neither benefit nor harm
Definition of mutualism
Association which is beneficial to both organisms involved
Definition of parasitism
1 organism, the parasite benefits at the expense of the other
Definition of obligate intracellular parasites
Can only reproduce within host cells
Definition of facultative parasites
Do not rely on its host to continue their life cycle
Can live and reproduce inside and outside cells
Definition of normal flora
Population of microorganisms that live in the skin, mucus membranes and GI tract of a healthy human body
Definition of human micribiome
Collection of all genes of all the microbes in normal flora
Definition of opportunistic infections
Caused by non pathogenic microbes that act pathogenic in certain circumstances
Definition of infection
Prescience of microbes in the body that are causing harm
Definition of colonisation
Describes when new microbes grow on superficial body sites (skin, mucus membranes, GI) without invading the body
Definition of carrier
Someone who harbours a microbe, a source of infection for others
Definition of pathogen
Microbe that can cause disease
Definition of microbial pathogenesis
Process by which infection => disease
Definition of immunopathogenesis
Primary cause of cell death in many infections, due to killing of infected cells by host immune systems
Definition of symptoms
Subjective features of a disease experienced only by the patient
Can be a symptomatic (subclinical) or symptomatic
Definition of a sign
Objective manifestation of disease that can be observed and measured by others
Definition of syndrome
Group of symptoms and signs characteristic of a disease
Definition of communicable
Infection spreads from host => host either directly or indirectly
Definition of contagious
Highly communicable disease spread by contact
Definition of non communicable
Infection non transmissible between humans
Definition of sporadic
Only occurs occasionally
Definition of endemic
Always present in a population, community, country
Definition of epidemic
Has greater no of cases than normal in an area within a short timeframe
Definition of pandemic
Epidemic disease that has a worldwide distribution
Definition of outcome
Balance between microbial replication and spread of hosts ability to respond/resist
Definition of acute infection
Rapid onset of disease, relatively brief period of symptoms
Pathogen cleared within days
Definition of a persistent infection
Pathogen not cleared from the host following the primary infection but stays in tissues of infected individuals
Definition of latent
Microbes persist after initial clearance, may have asymptomatic reactivation
Definition of chronic
Continued production of infectious organism and immune evasion
Are carriers
Definition of nosocomial infections
Any infection acquired in a hospital or medical facility
Can affect patients, health care workers and are common because
-Easily moved around by staff, patients, visitors
-Not always prevented by hand washing
Definition of host range
Different species of hosts a given pathogen can infect
Determined by interactions of viral proteins with cognate cellular receptors
Definition of tissue tropism
Different tissues within a given host that are infected by the pathogen
Definition of permissive cells
Allows pathogen to replicate
Has required receptors, lacks defences against pathogen/pathogen has evolved mechanism to overcome defences
Definition of pathogenicity
Ability of a microbe to cause disease
Definition of virulence
Degree of pathogenicity in a microbe
Definition of endotoxins
LPS in G-ve bacteria
Can induce inflammation and fever as an immune response
Definition of exotoxins
Secreted proteins by G+ve and -ve
Many mechanisms, targets => many diseases
Definition of superantigens
Toxins that stimulate the immune system without MHC II
What are the 4 types of host microbe associations
Symbiosis, close long term interaction between 2 species
Commensalism, 1 benefits, other not harmed or benefits
Mutualism, benefits both
Parasitism, 1 benefits, other harmed
What are the 2 ways for parasites to reproduce
Obligate intracellular
-only reproduce in hosts
Facultative parasites
-reproduce in and out of cells
What are the 3 functions of normal flora
When can they cause problems
Mucosal immunity dev
Protection against pathogenic colonisation
Digestion aid
Bacteria found outside reservoir
Changes in flora due to
-exogenous infection
-invasive technique, AB
What are the 3 properties of resident flora
What is the most common type
Can reestablish population
Not removed by handwashing
Not associated with infection spread
Staph epidermidis
What are the 3 properties of transient flora
Can’t reestablish population
Removed by handwashing
Associated with infection spread
Staph aureus
When can opportunistic infections occur
Normal flora found outside resevoirs
Host defenses weakened
Lack of normal flora competition
What is immunopathogenesis
What 2 réponses are possible?
The damage that occurs as a result of the immune response
- CD8 attack
- AB attack
- Complement attack
Local vs systemic
What 2 conditions lead to a syndrome
Symptoms,-subjective EXP of patient
Sign
-objective manifestation, can be observed/measured
What are the 4 steps needed for an infectious organism to thrive
Enter body
Evade immune system
Rapid growth
Transmission into next host
What are the 3/4 stages of disease progression
What factors affect the first stage
Incubation
Prodrome (not always present)
Illness
Recovery
Factors affecting incubation
- Virulence, dose
- Patient immunity
- Site
- Generation time
What are the 4 methods of infection classification
Transmission
- Communicable
- Non communicable (not spread between people)
Site
- Superficial
- Systemic
Occurence
- sporadic
- endemic
- epidemic
- pandemic
Outcome
- acute
- persistent => latent/chronic
How can we get nosocomial and iatrogenic infections
Infection acquired in HC environment
Disrupted mechanical barriers to infection
- foreign bodies easier to colonize
- injury associated with therapy => normally sterile areas are vulnerable
What 3 factors lead to AB resistance
Mutation
-transfer resistance genes via plasmids
Transmission
-via surfaces/hands of staff
AB
-incorrect, inappropriate use
Describe bacterial attachment methods
Describe viral attachment methods
Bacteria
-adhesins (glycolipid, capsule, pilo, proteins, polysaccharides) bind to receptors
Virus
- viral surface proteins bind to receptor => membrane fusion/penetration
- attachment factors concentrate viral particles at surface
What do these invasins do
- Collagensase/hyaluronidase
- coagulase
- leukocidin
- haemolysin
Collagenase/hyaluronidase
-BM degradation => spread via tissues
Coagulase
-fibrin forms => surrounds s aureus, protection from phagocytosis
Leukocidin
-WBC degradation
Haemolysin
-RBC degredation
What does the LD50, ID50 tell you about the virulence of a pathogen
LD50
-no of pathogens that kill 50% of hosts
ID50
-no of pathogens that infect 50% of hosts
What are the 2 main types of virulence factors in bacteria
Endotoxins
Exotoxins
What are the properties of endotoxins
- source
- secreted?
- molecule
- gene location
- toxicity
- clinical effects
- antigenicity
- heat stability
Source
-G-ve
Secreted?
-No
Molecule
-Lipopolysaccharide
Gene location
-chromosome
Toxicity
-low
Clinical effects
-fever, shock
Antigenicity
-poor
Heat stability
-stable at 100C
What are the properties of exotoxins
- source
- secreted?
- molecule
- gene location
- toxicity
- clinical effects
- antigenicity
- heat stability
Source
-G+-ve
Secreted?
-Yes
Molecule
-Polypeptide
Gene location
-plasmid
Toxicity
-high
Clinical effects
-variable
Antigenicity
-high
Heat stability
-destroyed rapidly at 60C
What 4 things do viral virulence factors do
Alter viral replication abilities
Modify host defences
Enable viral spread
Act as toxic proteins
What are super antigens
What do they do
Stimulate immune system, bind directly to MHC2 non specifically => many T cell stimulated
Example, E2 spike protein in coronavirus
