Bacterial properties Flashcards
Describe the basic structure of bacteria
- Small and unicellular
- No internal organelles (no chloroplasts, mitochondria)
- Haploid
- Some have flagella
Name the different shapes of bacteria
- Cocci
- Bacilli
- Spirilli
What is the difference between Gram-positive and Gram-negative bacteria?
POSITIVE:
- Thick peptidoglycan layer (retains violet dye well = deep violet stain)
- One membrane (cytoplasmic)
NEGATIVE:
- Thin peptidoglycan layer (violet dye is lost = cells absorb counterstain = appear pink)
- Two membranes (cytoplasmic and outer membranes)
Where is peptidoglycan found in gram+ and gram- bacteria?
POSITIVE = cell wall
NEGATIVE = in periplasm (area between the two membranes)
What feature is found only on Gram-negative cell walls?
- Lipopolysaccharide
- Found in outer membrane
Give examples of some Gram + and - pathogenic bacteria and the diseases they cause.
POSITIVE:
- Staphylococcus aureus (skin diseases, endocarditis, pneumonia)
- Streptococcus pneumoniae (pneumonia, meningitis)
- Streptococcus pyogenes (tonsillitis, scarlet fever)
NEGATIVE:
- Escherichia coli (EPEC - diarrhoea, EHEC - produces toxin, dysentery and kidney failure)
- Shigella (dysentery)
- Neisseria (meningitidis - meningitis, gonorrhoeae - gonorrhoea)
Give examples of some Mycobacteria and the diseases they cause
- Mycobacterium tuberculosis (TB)
- Mycobacterium leprae (leprosy)
NOTE: mycobacteria are neither gram+ or gram- (have a waxy cell wall)
What do bacterial pathogens do?
- Colonise
- Persist
- Replicate
- Disseminate within cells, tissues between organs and hosts
- Cause disease (dysregulate immune responses)
Apart from gram+ and gram-, what is another way of classifying bacteria?
Intracellular and extracellular pathogens
Give examples of some extracellular pathogens
- Staphylococcus
- Streptococcus
- Neisseria
Give examples of some intracellular pathogens
- Listeria
- Shigella
- Salmonella
- Mycobacteria
What are the three methods by which bacteria survive in the host cell?
- Escape
- Prevent fusion with lysosomes
- Survive in phagolysosome
Salmonella is an actively invading bacteria. Describe how it invades cells (which are not naturally phagocytic) by motility and invasion
Two structures: flagellum and injectisome
FLAGELLUM:
- Generates proton-motive force for movement
INJECTISOME:
- Transfers virulence proteins into host cells
- Causes actin polymerisation, membrane ruffling, bacterial internalisation
Describe another way in which actin is manipulated by bacteria
- Bacteria (such as listeria and shigella) can polymerise actin at one pole of the bacterium forming comet tails
- This polymerisation propels the bacterium through the cytoplasm
What are the 3 basic mechanisms for horizontal gene transfer (HGT)?
- Transformation
- Conjugation
- Transduction
Explain the mechanism of transformation in HGT
The uptake of naked DNA from the environment
E.g. Neisseria, Streptococcus
Explain the mechanism of conjugation in HGT
Transfer of genetic material in the form of a plasmid via a conjugation tube
Explain the mechanism of transduction in HGT
- Bacteriophages infect a bacterium and take up some of the bacterial DNA
- The bacteriophage then carries the bacterial DNA to another bacterium
What is a Pathogenicity Island?
Horizontally acquired genes that contribute to the virulence
Where do gram+ bacteria retain a violet dye?
In the peptidoglycan of their cell wall
Why is the stain excluded from gram- bacteria?
Excluded by the presence of an outer membrane
What is an obligate intracellular pathogen?
A pathogen that cannot be cultured freely on medium (e.g. Chlamydia)
Variation in vertically transmitted DNA can occur as a result of…?
Mutation
What is acid-fast bacteria?
- Have a waxy substance called mycolic acid in their cell walls which makes them impermeable to many staining procedures (inc. Gram stain)
- They are able to resist decolorisation with acid alcohol
