Pathogens Flashcards
What are the definitions of infection, pathogenicity, infectious disease, and opportunistic pathogen?
Infection = disease or no disease
Infectious disease = change in health state of host from carrying out normal activities
Opportunistic pathogen = cause infection away from typical niche or different environment
What are virulence and virulence factors?
Virulence = degree of harm inflicted on a host by a microorganism
Virulence factors = physical or chemical characteristics of a pathogen which contributes to the disease-causing process
What are pathogenicity and pathogenicity islands?
Pathogenicity = ability of a pathogen to cause disease
Pathogenicity islands = a group of genes encoding for virulence factors that can be transferred from bacteria-to-bacteria
What is the pattern of infection?
Incubation period = no signs / symptoms
Prodormal stage = onset of symptoms, unclear diagnosis
Illness period = severe, characteristic signs / symptoms
Recovery / conalescence
Infectious period will vary depending on the microorganism
Infection is a competition for resources and the host is a source of nutrients and energy. Therefore, the pathogen develops mechanisms to access and exploit the host. What are these mechanisms / the stages of infection?
Transmission Adherence Invasion Surviving (evasion of host defences) Damaging the host
How does transmission occur?
Direct transmission
- Physical contact
- Airborne (under 1m)
- Vector (insects, ticks, bats)
- Vertical contact (mum to baby)
Indirect transmission
- Contact
- Food / water / blood products
- Airborne, longer distances
What is adherence?
First steps in the infective process is adherence and invasion
Entry site = skin, oral, gut, respiratory tract, and eyes
Can be specific and non-specific
Achieved or assisted by pili (fimbriae) which are small, hairlike appendages on the surface of many bacteria
What occurs in the invasion process?
Pathogen actively or passively penetrates the mucous membrane or epithleium
Active invasion = virulence factors, proteases, hydrolyases, lysins, and toxins
What is bacteremia and septicemia?
Bacteremia = presence of viable bacteria in the circulating blood
Septicemia = infection disease in blood (blood poisoning)
How does a pathoen covercome innate / adaptive immune systems? How does it survive?
Overcomes resident microbiota through a variety of methods
- Secretion systems
- Replication inside hose cells (eg HIV)
- Hide between cells
- Decoy proteins
- Change surface proteins (eg influenza)
- Capsule to resemble host
- Biofilm = protects from nutrient deprivationn, antimicrobial agents and host immune cells
Virulence is the magnitude of harm a pathogen achieves, and virulence factors serve to increase virulence. What are different types of virulence factors?
Rapid replication
Integration of pathogen genome into hsoe to alter function
Use of toxins
How are toxins used to increase virulence?
Exotoxins = gram +ve, heat sensitive, travel in host and are extremely immunogenic (antibodies target the toxin and not the source)
Endotoxins = LPS on gram -ve and are heat stable - cause fever, shock etc
What are opportunistic infections?
Infections that are more frequent / more severe in people with weakened immune systems
Infections that arise from areas proximal or distal to the mouth (or source of infection)
What is an example of infection caused by a weakened immune system?
Frequent Ab uasage can lead to candida albicans / oral thrush
What is an example of infection caused by different niches?
Bacterial endocarditis (Streptococcus viridian is an oral commensal, previous rheumatic heart disease, combination leads to infection of damaged heart valves)
