Growth, Survival, and Death of Microbes Flashcards
What are the stages in the life cycle of a virus?
- Attachment of the virus to the surface of a susceptible, and becomes adsorbed
- Penetration whereby the virus enters the cell via fusion with the plasma membrane then entry via the endosome
- Uncoating where the genome needs to made available so that it can act on the host cell DNA
- Viral nucleic acids and proteins become synthesised in the nucleus and cytoplasm. Their assembly and maturation occurs in the nucleus, cytoplasm or the membrane
- Lysis occurs of the cell such that the viruses can be released from the cell. Budding is another method by which viruses can be released from the cells
What is the clinical significance of the stages in the life cycle of a virus?
All these stages can be targetted through vaccination or anti-viral therapy
What is a defective virus?
One that requires the assistance of another virus for its propagation
Give an example of a defective virus?
HDV
What does a HDV virus require for its propagation?
HBV
What is a viroid?
A naked ssRNA of less than 400 nucleotides
What are prions?
Extremely robust ‘proteinaceous infectious particles’ lacking nucleic acid.
It seems they are normal body proteins converted to an alternative configuration by contact with other prion proteins
Where are prions the causative agent?
In CJD
How is CJD transmitted
Humans eating infected cow meat
What do prions play a role in the development of?
Alzheimer’s disease
Why are prions involved in the development of Alzheimer’s disease?
There is the formation of insoluble deposits (prions) forming in the brain, leading to neural degeneration
How do bacteria multiply?
Binary fission
In what manner to bacteria propagate?
Exponentially
What are propagating bacteria known to be in?
The vegetative state of growth
What is the problem with bacteria in the stationary phase (i.e. not growing)?
They are more difficult to treat with antibiotics
What are spores?
High resistant structures that are formed by some bacteria
Why are spores highly resistant?
Because the bacteria are in the stationary state of growth, and are encapsulated in a tough coat
Where can bacteria grow?
- Agar
- Broth
- Biofilms
What do bacteria form when growing in agar?
Colonies
When can bacteria form biofilms?
In natural environments
Draw a diagram illustrating biofilm formation
What must bacteria have to grow?
- A suitable energy source
- Specific building blocks for growth
- Specific atmosphere
What specific building blocks for growth do bacteria need?
- Carbons
- Nitrogen
- Water
- Trace elements
What is the growth and survival of microbes very important in?
Maintaining the transmission of infection and sustaining the reserviors of infectious agents
When are organisms easier to eradicate?
When they can only survive and grow in humans
Give an example of an organism that can only survive and grow in humans?
Smallpox
When are organisms nearly impossible to eradicate?
When they have an environmental or animal reservior
What determines the disease development spread of a microbe?
The rate at which they grow
What kind of diseases have a rapid disease developement spread?
Those with acute onset
What is crucial with diseases witha rapid disease development spread?
Early diagnosis
Give an example of a disease with rapid disease development spread
Neisseria meningitides
What kind of diseases have a slower disease development spread?
Those that are slowly progressing
What is the result of a disease having a slower disease development spread?
Urgent diagnosis is not as crucial for the patient
Give an example of a disease with a slower disease development spread
Mycobacterium tuberculosis causing TB
What is the latent period in the growth of a microbe?
The time between first initial infection and presentation of symptoms
What are the main ways that bacteria can develop antibiotic resistance?
- Intrinsic resistance
- Extrinsic resistance
What happens in intrinsic resistance?
The bacteria undergo a genetic mutation within their own genetic information to develop a means of becoming resistant to a specific or group of antibiotics
What happens in extrinsic resistance?
The transfer of genetic material occurs between bacteria
How can extrinsic resistance occur?
- Transformation
- Conjugated
- Trasduction
What happens in transformation of bacteria?
Uptake of naked DNA and incorporation into their own genome
What is the result of transformation of bacteria?
The bacteria now has the genes to develop the antibiotic resistance the original bacterium had
What happens in conjugation of bacteria?
The bacteria can use plasmid DNA to develop antibiotic resistance
What are plasmids?
Circular DNA structures found in the bacterial cytoplasm that can code for many genes, including antibiotic resistance
What can bacterial conjugation cause?
Rapid spread of resistance amongst bacterial colonies
What happens in transduction in bacteria?
Resistance genes are mobilised by the action of some bacteriophages
By what mechanisms can bacteria have antibiotic resistance?
- Antibiotic modification
- Impermeability
- Efflux mechanisms
- Alteration of the target site
What are the types of antibiotic modification?
- Enzyme inactivation
- Enzyme addition
What happens in enzyme inactivation?
The organisms will produce enzymes that degrade the antibiotic and inactivates it
Give an example of an enzyme that can degrade antibiotics?
ß-lactamase
What does ß-lactamase do?
Breaks open the ß-lactam ring of penicillins and inactivates it
What happens in enzyme addition?
The organism expresses an enzyme which can add a group to the antibiotic and inhibits its activity
Give an example of antibiotic resistance by enzyme addition
Resistance to aminoglycosides by addition of acetyl or amino groups
What is meant by impermeability?
With respect to bacterial resistance
When the bacteria become resitant to antibiotics as their cell envelope is impermeable to particular antibiotics
Give two examples of antibiotics where bacteria have become resistant through impermeability
- Pseudomonas spp.
- ß-lactam
Give an example of an efflux mechanism of antibiotic resistance
The bacteria can pump the antibiotic out of the cell by a newly coded for protein
Give an example of a case of resistance by pumping antibiotics out of the cell by a newly coded for protein
E. Coli to tetracyclins
What does alteration of the target site involve?
The alteration to the target that the antibiotic normally takes to become resistant to the antibiotic
Give an example of bacterial resistance through alteration of the target site
Resistance to rafampicin, which inhibits the ß-subunit of RNA polymerase, where the RNA polymerase gene becomes altered to new RNA polymerase is not affected by rifampicin
What must be done to medical equipment to reduce infection rates?
Remove the microbes that contaminate them on a daily basis
What is sterilisation?
The inactivation of all self-propagating biological entities associated with the material or the area under consideration
Why is sterilisation very hard to achieve?
Due to the presence of prions or spores
What is used to sterilise surgical instruments in a clinical setting?
An autoclave
What does an autoclave do to remove microorganisms?
Pressure and high temperature steam
Other than an autoclave, how can surgical equipment be sterilised?
Radiation
What is disinfection?
The removal of pathogenic organisms to a level where they no longer constitute a risk to individuals
What is the advantage of disinfection over sterilisation?
It is much easier to achieve
What is antisepsis?
Disinfection applied to human tissues
How can disinfection be acheived?
- Physical processes
- Chemical processes
What physical processes can achieve disinfection?
- Filtration of air
- Heat
- Radiation
What chemical processes can achieve disinfection?
Liquid or gaseous agents
