Bacteria, Viruses, Fungi, Protozoa, Helminths Flashcards
Define symbiosis
A relationship between two organisms
Define Parasitism
An organism that lives in or on a host that causes disease
Define commensalism
a relationship between two species where one species obtains food or other benefits from the other without causing harm or benefit to the host.
What are the characteristics of a typical prokaryotic cell?
Circular DNA
Asexual reprodution
Unicellular
Cell division by binary fission
Name 3 differences between prokaroytic and eukaryotic cells
Prokaryotes: Small cells, unicellular,no membrane bound organelles, circular DNA, divide by binary fission
Eukaryotes: Large cells, membrane bound organelles, cell division by mitosis or meiosis,
What is the difference between gram negative and gram positive bacteria?
Gram negative bacteria have a thin layer of peptidoglycan and an LPS layer
Gram positive bacteria have a thick layer of peptidoglycan
Describe the mechanisms of lateral gene transfer in bacteria
Lateral gene transfer occurs whenever genes are transferred from one cell to another independently of the normal inheritance process. Three methods are: transduction, transformation, conjugation
Transduction: DNA is transfered from cell to cell by bacteriophage
Transformation: free DNA is incorporated into competent recipient cells
Conjugation: transfer of plasmid DNA from a donor cell which contains an F pilus, to a recipient cell which does not. Transfer of DNA is via rolling circle replication.
Describe the mechanism of bacterial conjugation
Conjugation requires direct contact between donor and recipient cells.
The donor cell contains a conjugative plasmid (has an F pilus) which makes contact with the recipient cell and the cells are drawn together.
Conjugation is triggered by cell-cell contact and DNA is transfered to the recipient cell via rolling circle replication of the plasmid DNA.
At the end of the process both donor and receipient have the plasmid
Define infection
the establishment of an organism within a host
Define Pathogen
any organism that has the capacity to cause disease
Define virulence
quantitative measure of pathogenicity or the likelihood of causing disease
What are virulence factors?
Pathogen produced extracellular proteins that enable a microorgansm to establish itself and replicate on or within a specific host species, and enhance the microbe’s potential to cause disease
What are opportunistic pathogens?
AN organism that causes the disease in the absence of normal host resistance i.e. when there is deficiency in the immune defense
Describe the role of virulence factors in bacterial infections
Virulence factors enhance colonisation and growth
- Aid colonisaton: express adhesion molecules which specifically adhere to cells in a region of the body. Interactions between the bacteria and host epithelium trigger entry (invasion)
- Aid survival: Produce factors which allow the bacteria to evade the immune system e.g. capsule which prevents phagocytosis, molecular mimicry, intracellular invasion
- Damage the host: produce enzymes and toxins which target host cells and tissues, resulting in cell lysis and tissue damage
- Obtain nutrients: Enzymes and toxins degrade host tissue and cause cell damage, products (proteins, nucleic acids) taken up by the bacteria. Produce proteins that chelate iron and Ca2+
What are the obligatory steps for infection
Exposure to pathogen
Attachment and entry into the body
Adherence to the skin or mucosa by evading the natural protective mechanisms of the host
Invasion through the epithelium
Colonisation and growth (produces virulence factors).
Evasion of host immune defences . Allows further growth and local or general spread
Growth and colonisation can result in toxicity (effects can be local or systemic), invasiveness (further growth at original site and distant sites) both of which cause further tissue damage.
