W1 Microbiology and pathogenicity lecture Flashcards
Define microbe.
Any organism that is too small to be seen by the visible eye, this includes some bacteria, viruses, fungi and parasites.
What is a pathogen?
A microorganism that parasitizes a host and causes disease.
What are the two single-celled morphologies for bacteria?
cocci (round/circle)
bacilli (rod shaped)
What are the different formation of cocci bacteria?
Monococcus - single cell
Dicoccus - paired cell
Staphylococcus - grouped cells
Streptococcus - chained cells aka one long line.
How do the different formulations of bacteria arise?
Depend on how the bacteria replicate.
What are the different formulations of rod shaped bacteria?
single rod - bacillus
Grouped / clustered
Chain - in one long continuous line.
Draw a diagram with labelled components of a typical bacterial cell.
What is significant in regards to protein synthesis about a prokaryotic cell having a nucleoid rather than a nucleus?
Genetic material is more accessible.
More rapid protein synthesis - also explained by ribosomes free in cytoplasm, lack secluded membrane bound organelles.
What is the role of pilli?
Mobility and adhesion (not in all bacteria)
What is an inclusion body in relation to a prokaryote?
An aggregate of recombinant protein found in the cytoplasm, often made from the expression of genes that the bacteria has taken in from another species or bacterium (non-self).
Describe the cell wall complex structure of gram-positive and gram-negative bacteria?
Gram-positive have a thicker outer layer of peptoglycan in their cell wall, with an inner cell surface plasma membrane
Gram-negative bacteria have a thin outer plasma membrane, then a thinner peptoglycan cell wall, followed by the inner cell surface membrane.
What is the periplasmic space?
What is its function?
In gram negative bacteria the periplasmic space is the space between the inner and outer membrane including the peptoglycan cell wall.
In gram positive bacteria the periplasmic space is the smaller gap between the inner membrane and the peptoglycan cell wall.
This space contains enzymes and substances that could be toxic within the cell cytoplasm. This allows it to play a role in protein processing, molecule synthesis and protection from turgor pressure.
What is the significance in the difference in size in the periplasmic space between gram-positive and gram-negative bacteria?
Gram-negative bacteria have a larger periplasmic space, so are more protected from turgor pressure and have a higher level of protein manipulation and synthesis before molecules enter the cytoplasm.
Explain how the outer and inner membrane both play a role in substances entering a gram-negative bacterial cell?
Outer membrane has larger pores, allows larger substances to enter the periplasmic space.
Larger molecules are broken down or processed by proteins/enzymes in the perisplasmic space.
This means they are made smaller so are able to enter through the smaller pores found in the inner membrane.
What are bacterial spores?
Spores are produced by SOME bacteria during environmental hostility.
They contain a copy of bacterial DNA.
Often dehydrated with little cytoplasm or content.
They are released in the dormant form and are surrounded by multiple layers that make them more resistant to conditions such as high temperature, UV and oxidation.
Hence are more likely to survive the extreme environment conditions.
Spores are able to sense a relaxation in environmental conditions then change their mechanisms to germinate another bacterial colony.
Why are bacterial spores important clincally?
Allow bacteria to survive more hostile conditions, meaning specialist cleaning methods are often needed if contamination occurs.
Bacteria that produce spores are more likely to survive and spread so are more difficult to treat.
Bacteris that produce spores are more likely to have a less controlled spread.
What are the stages of treatment for an infectious disease?
Observations of patients symptoms
Take a sample of bacteria from patient
Grow a culture in a lab, make observations and test to identify the bacteria.
Give appropriate treatment often antibiotics.
Observe the wider population (epidemiology)
Prevent further transmission.
What is empirical prescription and why is this important to antibiotic resistance?
Prescribing a treatment based only on symptoms, no identification test.
More likely to prescribe antibiotics for a viral infection.
How does a hospital infection outbreak vary from a community outbreak?
Hospital is a more closed environment.
Patients more vulnerable to infection
More likely to be an antibiotic resistant strain.
Faster pace of spread.
What is an infectious disease?
Due to infection by a pathogen.
What is meant by infection?
The invasion by and multiplication of a pathogenic microbe within a host.
What is contamination?
The presence of microbes in an environment/location.
What are Koch Postulates?
The four criteria Koch used to prove a microbial cause behind a disease.
1. The microbial cause must be observed in every incidence of the disease
2. Microbe must be isolated from diseased host and grown in a culture.
3. Culture when given to a healthy person must cause the same disease
4. Microbe must be re isolated from the second individual.
What are some faults in Koch’s Postulates?
It is difficult to isolate microbes in their pure form.
The way a disease presents itself may vary from person to person.
Bacteria mutates quickly, genetic fingerprint may change between hosts so no-longer be an identical cause.
What is an important note from looking at the different sites and types of infections?
The same pathogen can infect multiple different sites.
Similarly the same body site can be infected by multiple different pathogens.
What does the iceberg concept of infection show?
Only a small proportion of people exposed to an infection will get severe symptoms are seek help.
There will be increasing more people who have mild symptoms, do not have symptoms, were exposed but did not catch the infection.
Why is the icebergy concept of infection important clinically?
Shows the difficulties of controlling infection rates.
A larger proportion will have an infection than the number that presents to medical services.
What are the key stages in disease progression?
- Encounter
- Entry/establishment
- Colonisation (including spread, multiplication, damage and outcome) - may be commensal or pathogenic.
What does successful transmission for a microbe depend on?
The number of microbes (higher=more likley)
The size, density and surface features.
Hydrophobicity( water borne only)
Resistance to dessication, spore formation and ahesion to surfaces (contact)
Open routes into host e.g cuts
Vector availiability.
How does hydrophobicity impact has easily a microbe pass between hosts?
A more hydrophobic microbe will float on the surface of the water, so is more likely to be included in drinking water taken from open sources, so is more likely to have a successful transimission.
What factors affect adherence and invasion of a microbe to a host?
Depend on microbe and host features
Break is host surface layer
Attachment is often by pilli
Proteases to penetrate epithelium
Capsules increase chance of survival increase phagosomes and have sticky carbohydrates for adhesion
Some virus may injected epithelial cells with molecules (DNA) to change surface features e.g transcribe for receptors for viral attachment.
What are some consequences of disease success?
What factors influenced how successful a disease is?
A microbe may or may not be pathogenic
Host cells resist defences e.g neutralising toxins,
adaptive and innate immunity.
Microbe growth may also be limited by the availability of nutrients such as iron.
Microbes may cause tissue damage by accumulation of toxins or digestive enzymes.
What is normal or commensal flora?
Organisms that live in benign symbiosis with the host.
Same microbes may be pathogenic but unable to enter the disease process,
conditions may change e.g during stress, which causes the microbes to become pathogenic.
What is tissue remodelling?
Causes by prolonged inflammation leading to tissue damage, structure and function of tissue is damaged and changes.
Define pathogenicity
The ability of a pathogen to create an infectious disease in an organism.
Define virulence.
The severity of disease/degree of damage caused by a microbe.
Define virulence/pathogenicty factor
A microbial property or process that contributes to the virulence/pathogenicity of a pathogen.
