Microbiology Lecture 2 Flashcards
Define resolution.
Smallest distance between two points where they can be seen as separate.
To what distance is light microscope limited? What about electron microscopes?
Light
0.2um - 1,000x
Electron
0.2nm - 200,000x
Can viruses be seen on a light microscope?
No.
What is necessary when using a 100x objective lens on a light microscope, and why?
Immersion oil. It prevents excess diffraction and bends light within the oil.
Name and describe the four steps of gram staining, a chemical commonly used for each step, and how each step affects the colour of the cells.
Primary stain - cells stained with crystal violet - all cells become purple.
Mordant - cells stained with iodine - crystal violet cannot leave gram + cells only.
Decolourisation - cells rinsed with acetone - gram negative cells lose their colour.
Counterstain - cells stained with safranin or carbol fuschin - gram negative cells become red/pink.
What does the differential staining of gram staining rely on?
Differences in cell wall structure.
What is the cell wall of gram positive cells like? Can water go in or out?
Base plasma membrane
Coated in a thick layer of peptidoglycan.
Water cannot enter or leave.
What is the cell wall of gram negative cells like? Can water go in or out?
Base plasma membrane
Coated in a thin layer of peptidoglycan.
Has an outer plasma membrane, with lipopolysaccharide endotoxins on the surface - the lipopolysaccharide layer.
Water can pass in and out.
What are the components of the lipopolysaccharide endotoxins seen on the surface of gram negative bacteria?
O polysaccharide, Lipid A
Which type of bacteria is better at surviving desiccation, positive or negative?
Positive, as water cannot enter or leave their thick peptidoglycan layer.
How are peptidoglycan walls formed and which enzyme is involved?
Strands of peptidoglycan form via tetrapeptide crosslinks, catalysed by transpeptidase.
What process allows penicillin to function effectively as an antibiotic, and how does it do so?
Before the cell wall expands, existing tetrapeptide crosslinks are broken by autolysins.
Penicillin binds to transpeptidase, preventing new bonds from forming, and leaving the cell wall weak.
Can water contaminated with gram negative bacteria be sterilised? Why?
No, endotoxins remain in the water and arent inactivated. Causes endotoxic shock if used for medical purposes.
Must be filtered not sterilised.
Name 3 gram negative bacteria.
Salmonella, shigella, E. coli
Can all bacteria be stained by gram staining?
No, mycoplasma cant as it has no cell wall.
