Pathogens Flashcards
Define mutualism….
A relationship between two organisms which is mutually beneficial to both parties
One cannot survive without the other
Example - ruminants and gut bacteria
Define symbiosis..
A close and prolonged relationship between two organisms of different species.
There are several types of symbiotic relationship including mutualism, commensalism and parasitism
Define commensalism……
A relationship where one benefits while the other is unaffected
An example of a commensal organism is the bacteria in and on our bodies. They do us no harm but we provide nutrients and protection etc
Commensals can become pathogens if moved to a different area of the body for where they normally live
What is an endogenous infection?
An infection caused by an agent originating in an individuals own body
An example is cystitis which originates from faecal bacteria infecting the urethra
What is an exogenous infection?
An infection caused by an agent outside of the individual’s body
Define parasitism…
A relationship between two organisms where one lives on/in the other (parasite) at the expense of the other organism (host)
List the biological agents responsible for human infectious disease…
Viruses Prions Bacteria Protists Fungi Invertebrate parasites Arthropods Helminth
List Koch’s postulates
An organism is pathogenic if:
1 it is present in every case, and at all sites, of the disease
2 it can be isolated from the diseased host and be grown in pure culture
(i.e. free of any other microbe) on articial media
3 a sample of this pure microbial culture is introduced into a suitable
experimental animal and symptoms of the disease occur in this new host
4 it can be recovered from disease lesions in this experimental host animal
Define aetiology….
Underlying causes of disease
What is a zoonose?
A pathogen which can be transmitted from animals to humans
Name the three main driving factors for disease emergence
1 Host-related factors:
population growth, urbanisation, travel, migration.
The ease with which people now travel around the world means that the
topic of emerging infectious diseases is often in the news.
2 Pathogen-related factors:
capacity to adapt to humans and to acquire
virulence factors, antibiotic resistance.
3 Environmental factors:
land use, agricultural practices, food production,
food and water supply, animal trade, climate change.
Name the features an organism must have to successfully invade a host….
°
It must be able to attach itself to a host, and either remain on the exterior and spread locally, or enter the hosts body.
If it does enter the hosts body, it must reproduce and let progeny exit the body where
they may find a new host.
Evade the hosts immune response and other defences against infection.
What is an opportunistic pathogen?
An organism that can only cause disease in an individual whose defences have been compromised in some way for example, by injury, drugs or another disease
Define an antigen….
Any molecule which is recognised by the immune system
There are non self antigens, self antigens and auto antigens
Can be found on the surface of pathogens as well as inside, only becoming visible when excreted or when the pathogen is degraded
Antigens are usually large complex proteins. They can also be glycolipids or polysaccharides which are found on bacteria and protists
Define an antibody….
Glycoproteins produced by B lymphocytes which bind specifically and non-covalently to antigens
Antibodies are also immunoglobins (Ig) (globular proteins involved in immunity) and there are five classes
IgG
IgA
IgM
IgD
IgE
What is a pyrogen?
A fever inducing substance
List the modes of transmission for infection
Human to Hunan transmission routes.... Respiratory or salivary Faecal to oral route (waterborne) Genital transmission Skin contact
Vector
Biting arthropod
Zoonoses
Animal to human transmission - vertebrate reservoir
Define horizontal transmission…
When an infectious agent is passed from one person to another
Define vertical transmission…
When an parent transfers an infection to the next generation via sperm, egg, intrauterine infection, during birth, via breast feeding
List the barriers to direct transmission…
Skin - hard layer of dead cells. pH of 5.5 and sodium chloride found in sweat makes uncomfortable conditions for microbes
When sunlight falls on the skin it catalysed ROS which damage both skin and microbes
Commensal bacteria produce antimicrobial peptides
Lysozyme is produced by tears, saliva, seminal fluid and degrades the peptidoglycan in bacterial cell walls
What is the mucociliary escalator?
Cilia within the lower respiratory tract beat mucous up and out of the lungs so it can be swallowed
Define aseptic….
Free of agents of disease
Define sterile….
Free of any living material
What is a fomite?
A contaminated surface or object…i.e a door handle or a surface which has been sneezed on by an infected person
