Bacterial Properties Flashcards
What is the difference between Gram-negative and Gram-positive bacteria?
Gram-negative bacteria have a thin peptidoglycan layer with two membranes (cytoplasmic and outer membranes)
stains pink
Gram-positive bacteria have a thick peptidoglycan layer, which retains the dye well. It only has one membrane
stains purple
Give examples of some Gram-negative pathogenic bacteria and the diseases they cause.
E. coli – diarrhoea, dysentery, kidney failure
Salmonella - food poisoning, typhoid
Shigella – dysentery
Neisseria – meningitis + gonorrhoea
Vibrio cholerae - cholera
What feature is found only on Gram-negative cell walls?
Lipopolysaccharide
Give examples of some Gram-positive pathogenic bacteria and the diseases they cause.
Staphylococcus aureus – skin infections, endocarditis, bacteraemia, pneumonia
Streptococcus pneumoniae – pneumonia, meningitis, otitis media
Streptococcus pyogenes – tonsillitis, necrotising fasciitis, scarlet fever
Give examples of some Mycobaceria and the diseases they cause
Mycobacterium tuberculosis – TB
Mycobacterius leprae - leprosy
What is another way of classifying bacteria?
Intracellular and Extracellular pathogens
Give examples of some extracellular pathogens.
Staphylococcus
Streptococcus
Neisseria
Yersinia
What are the three methods by which bacteria survive in the host cell?
(intracellular)
- Escape
- Preventing fusion with lysosome
- Surviving in the phagolysosome
Give examples of bacteria that survive using each of the above methods.
Escape – Listeria, Shigella
Prevent fusion of lysosome – Salmonella, Mycobacteria, Chlamydia
Survive in phagolysosome - Coxiella
Motility and Invasion require which two multi-protein machines?
Flagella
Type III Secretion system
Describe the role of the type III secretion system.
- A protein machine assembles which provides a channel (translocon) through which virulence proteins (effectors) can be injected into the host cell
- The virulence proteins then stimulate actin polymerisation and membrane ruffling which allows bacterial internalisation
- Gram-positive bacteria don’t have the type III secretion system
Describe another way in which actin is manipulated by bacteria.
Bacteria (such as listeria and shigella)
- breaks out of the vacuole
- assembles actin at one pole of the bacterial cell
- This polymerisation of actin generates force
which propels the bacterium - This leads to the spread of the bacterium from one cell to another
- These streams of actin are known as COMET TAILS
What are the three mechanisms of horizontal gene transmission?
- Transformation
- Transduction
- Conjugation
Bacteria can take up DNA from the environment
Explain each of the three mechanisms of horizontal gene transmission.
briefly
Transformation – the uptake of naked DNA from the environment
Transduction – bacteriophages infect a bacterium and take up some of the bacterial DNA. The bacteriophage then carries the bacterial DNA to another bacterium.
Conjugation – transfer of genetic material in the form of a plasmid via a conjugation tube
What is a Pathogenicity Island?
Horizontally acquired genes that contribute to the virulence
- contributes to evolution of bacterial pathogens
- bacteria occupy a huge component of the biodiversity in the world.
- he high reproductive rate and ability to mix DNA means that there is huge selection pressure among bacteria making them very sophisticated.
show diagram of gram positive bacteria
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show diagram of gram negative bacteria
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what features do both types of bacterial have?
what protein does only g neg have?
- Both membranes have embedded channel proteins
- the outer membrane consists of mainly LPS
- therefore LPS is only present in gram negative bacterial cells
what do bacterial pathogens need to be able to do?
- colonise - clings onto surfaces
- persist - ability to avoid the host defences
- replicate - acquires nutrients needed for replication
- disseminate within cells
- causes disease - produces toxins that kill cells
how does samonella motility and invasion work?
- they polymerise actin into filaments
- this ruffles the plasma membrane and means the bacteria get stuck
- as the process ends l the trapped bacteria is internalised
the function and structure of flagella?
- allows the propulsion of the bacteria through the fluids
- they are filamentous structures and they rotate
genome of bacteria?
- 500 -4500
much bigger than viruses
what is the core genome and non core genome?
- core genome = all the bacteria of a species have these genes - these are
housekeeping genes - 60% non-core genes,
explain transformation
- this is the uptake of naked DNA
- They can recognise naked DNA
- They have transport mechanisms which
allow uptake of this DNA and incorporation
into the bacterial chromosome - Neisseria and Streptococcus
explain transduction
- transfer of DNA by bacteriophage
- When phages invade bacteria, it replicates its DNA in the bacterium and cuts the bacterial DNA into small pieces
- some bacterial DNA is packaged into phage heads
- New phage particles are released
- The phage particles injects the bacterial
DNA from the previous bacterium it
infected into the next bacterium. - Injected DNA may be incorporated into the
bacterial chromosome
lots of DNA can do this
explain conjugation
You get a physical bridge between bacteria, which allows the transfer of a plasmid between the bacteria.
