IAI - pathogenesis of microbial infection Flashcards
what is symbiosis?
the close and often long-term interaction between two different
biological species.
what are the 3 types of symbiotic associations:
Commensalism
Mutualism
Parasitism
what is commensalism
- Commensalism: one organism benefits and the other derives neither benefit nor harm
what is mutualism
- Mutualism: association which is beneficial to both organisms involved
what is parasitism
- Parasitism: one organism, the parasite, benefits at the expense of the other.
what is the difference between Obligate intracellular parasites and facultative parasite
Obligate intracellular parasitescan only reproduce WITHIN host cells whilst facultative parasites do not rely on its host to continue their life-cycle as can live and reproduce inside AND outside cells
What is the definition of normal flora?
population of microorganisms that reside in the skin, mucous membranes and intestinal tract of healthy human body
What are the functions of normal flora?
- Helps development of mucosal immunity.
- Protects host from colonisation with pathogenic microbes.
- Aids in digestion of food.
What is the human microbiome?
collection of genes of all the microbes in normal flora.
What is the difference between resident and transient flora?
What changes in flora occur due to hospitalisation?
- Exogenous environmental infections (e.g. hospital flora found on linen, equipment, water supply)
- Invasive techniques employed increase risk of infection (e.g. urinary catheters, I.V. lines)
- Use of antibiotics
Define infection.
Infection is the presence of microorganisms in the body
Define colonisation.
Colonisation describes when a new microorganism grows on superficial body sites (skin, mucous membranes and GI tract) without invading the body.
Define carrier.
A carrier is a person who harbours a microorganism and can be a source of infection for others.
Define pathogen.
A pathogen is a microorganism capable of causing disease.
Define microbial pathogenesis.
Microbial pathogenesis is the process by which infection leads to disease
What is immunopathogenesis?
Immunopathogenesis is a primary cause of cell death in many infections is due to killing of infected cells by the host immune system:
- Cytotoxic T cell mediated attack(e.g. Hepatitis B virus and liver damage)
- Antibody-mediated damage to the host (e.g. Streptococcus pyogenes and rheumatic fever)
- Antibody-mediated complement fixation (e.g. Hepatitis C virus exploits the complement system to establish persistence)
What are 3 clinical manifestations of disease?
- Symptoms: Subjective features of disease experienced only by the patient. Infections can be asymptomatic (sub-clinical) or symptomatic
- Sign: Objective manifestations of disease that can be observed and measured by others
- Syndrome: Group of symptoms and signs characteristic of a disease
What are the 4 stages of infectious disease progression?
- Incubation: Time between exposure and onset of a specific clinical sign.
- Prodrome: Period during which non specific “constitutional” symptoms occur (e.g. fever, malaise, loss of appetite). Not all infectious diseases have a prodromal stage.
- Illness: Period during which the clinical features of the infection are manifests.
- Recovery (convalescence): Period during which the illness abates and patient returns to the healthy state.
What are the 4 types of infections based on occurrence?
Sporadic: the disease occurs only occasionally (e.g. tetanus)
Endemic: the disease is continously present in a population, community or country (e.g. TB and chickenpox)
Epidemic: the disease has greater number of cases than normal in an area within a short period of time i.e. outbreaks occur (e.g. SARS in 2003)
Pandemic: epidemic disease that has worldwide distribution (e.g. flu pandemic in 1918 and 2009)
Define outcome (based on infection terms).
Outcome – balance between microbial replication and spread and the host’s ability to respond/resist
2 types of persistent infections?
- Latent: the microorganism persists after initial clearance, and may have asymptomatic or symptomatic reactivation (e.g. latent tuberculosis, herpes simplex virus and varicella zoster)
- Chronic: with continued production of the infectious organism and immune evasion (e.g. chronic diabetic foot infection, hepatitis B, HIV). Infected hosts are carriers.
What are nosocomial infections?
Any infection acquired in a hospital or medical facility. Can affect patients
and health care workers and are common because: (i) are easily moved around by staff,
patients or visitors and (ii) not always can be prevented by proper hand washing.
What are 5 determinants of pathogenesis in a host?
- Age (e.g. Infants and elderly are more susceptible to influenza infection)
- Underlying characteristics that increase susceptibility (e.g. asthma, obesity, diabetes, malnutrition)
- Genetic variation (e.g. sickle cell trait provides protection to malaria; HIV long-term non- progressors)
- Immunodeficiency (e.g. opportunistic infections in AIDS patients)
- Immune response (e.g. “cytokine storm” in influenza infection)
- Trauma/surgery/foreign body (e.g. surgical implants make it easier for bacteria to cause infection and more difficult to eradicate it)
What are iatrogenic infections?
Factors that can disrupt the body’s non-specific mechanical barriers to infection make it easier for microorganisms to cause infection, ie:
- Injury associated with therapy
- Plastic and metal “foreign bodies”
What are 5 determinants of pathogenesis of an organism?
- Opportunism
- Attachment
- Invasiveness
- Virulence
- Effects of infection on cells (Cellular Pathogenesis)
What is tissue tropism?
the specific preference or affinity that a virus or pathogen has for infecting particular types of cells or tissues within a host organism. (e.g. rhinoviruses infect only the respiratory tract).
what determines tissue tropism?
Attachment is one of several factors that determine tissue tropism as the need for a specific cell receptor narrows the species and the type of cells the pathogen can enter.
What is a permissive cell?
A permissive cell is one that allows a pathogen to replicate.
What is pathogenicity?
Pathogenicity is the ability of a microbe to cause disease.
What are the 4 bacterial virulence factors?
- Adhesins
- invasins.
- Endotoxins: Lipopolysaccharides(LPS) present in the cell wall of Gram-negative bacteria.
- Exotoxins: Secreted proteins produced by Gram-positive and Gram-negative bacteria .
What are superantigens (SAgs)?
Superantigens (SAgs) are toxins that stimulate the immune system.
SAgs do not require processing to small peptides. They can bind to MHC-II molecules non-specifically and stimulate a large number of T cells.
do keats quiz on pathogenesis of microbial infection
https://keats.kcl.ac.uk/mod/lesson/view.php?id=6620871
what are 4 types of invasins
- Collagenase and hyaluronidase: Degrade collagen and hyaluronic acid disrupting the epithelial basal lamina and allowing bacteria to spread through subcutaneous tissues (e.g. S. pyogenes)
- Coagulase: Triggers the formation of a fibrin clot around the bacteria to protect them from phagocytosis (e.g. S. aureus)
- Leukocidins: Degrade white blood cells (e.g. S. aureus)
- Hemolysins: Degrade red blood cells (e.g. Streptococci, staphylococci and clostridia )
Prodrome is one of the four stages
of disease progression always observed in an infectious disease
true or false
FALSE - Not all infectious diseases have a prodromal stage.
what is incubation in the 4 stages of infectious disease progression?
Time between exposure and onset of a specific clinical sign.
what is Prodrome in the 4 stages of infectious disease progression?
Period during which non specific “constitutional” symptoms occur (e.g. fever, malaise, loss of appetite). Not all infectious diseases have a prodromal stage.
what is Illness in the 4 stages of infectious disease progression?
- Period during which the clinical features of the infection are manifests.
what is convalescence in the 4 stages of infectious disease progression?
Period during which the illness abates and patient returns to the healthy state.
