Lecture 1- Bacterial Properties Flashcards
Define the term ‘acid fastness’
The ability of cells to resists decolorisation by acids during lab staining procedures
What is the purpose of gram staining
to distinguish between two different kinds of bacterial cell walls
Describe the process of gram staining
- bacteria stained with crystal violet
- Washed with iodine which acts as mordant
- rinsed in alcohol to remove stain
- stained with counterstain (safranin)
What colour do gram +ve bacteria stain?
- stains deep violet because thick peptidoglycan retains dye
- only one layer
What colour do gram -ve bacteria stain?
- stains pink from counterstain because of thin peptidoglycan layer
Describe the structure of gram negative cell walls
- has two membranes
- a thin peptidoglycan layer
- thick lipopolysaccharide layer on top
- LPS layer had lipoprotein and this layer = PAMP
What are mycobacteria? Give examples
Don’t fall into Gram-ve or Gram+ve category
- M. tuberculosis
- M. leprae
Give examples of gram -ve
- E. coli (EPEC- diarrhoea, EHEC- toxin–> dysentary+ kidney failure)
- Salmonella (typhimurium- food poisoning, type- typhoid)
- Shigella (dysentary)
- Vibrio cholera (cholera)
neisseria (meningitides and gonorrhoea)
Give examples of gram positive bacteria
Staphylococcus aureus (skin disease, endocarditis, bacteraemia) Strep pneumonia Strep pyogenies (tonsillitis, scarlet fever, bacteremia)
What must bacterial pathogens be able to do to infect?
1) Colonize (using pilli and fimbriae to cling)
2) Persist (avoid the host immune system)
3) Replicate (acquire nutrients)
4) Disseminate (within cells, tissues, organs and hosts)
5) Cause disease
Name some extracellular pathogens
Staph, Strep, Yersinia and Neisseria
What are the three ways of surviving in the host cell? Give examples for each of the methods
1) ESCAPE from endosomes and phagosomes (Listeria, Shigella)
2) Prevent FUSION with lysosomes (Salmonella, Mycobacteria)
3) SURVIVE in Phagosome (Coxiella)
Which two structures help salmonella with invasion?
1) Flagellum- rotatory filamentous structures for movement
2) Type III secretion system
What is the function of the injectisome in salmonella?
1) Delivers bacterial virulence proteins
2) This causes actin polymerisation into filaments
3) —> Membrane ruffling
4) –> Bacterial internalisation
What type of bacteria are injectisomes found on?
Gram Negative bacteria
How do Listeria infect the host?
1) Phagocytosis by zipper mechanism into vesicle
2) Breaks out of vacuole
3) Polymerises actin at one end of cell
4) Uses this actin for propulsion
5) Forms streams of actin called COMET TAILS
What is the core genome in bacteria?
Housekeeping genes expressed in all bacteria
How do bacteria replicate?
By binary fission ( so daughter cells are identical to parent cells)
What are the three different types of horizontal gene transfer?
Transformation
Transduction
Conjugation
What is transformation? Which bacteria do this?
Incorporation of naked DNA (DNA from lysis of bacteria) from the environment
- Neisseria
- Streptococcus
What is transduction?
Incorporation of host bacterial DNA into invading bacteriophage genomes which are then incorporated into the next host’s DNA
What is conjugation?
Transfer of bacterial plasmid DNA to neighbouring bacteria through sex pillus
What are pathogenicity islands?
Horizontally acquired DNA that contribute to virulence. They are flanked by core host genes and tRNA genes.