Bacteria Intro

Question 1

Difference between gram positive vs gram negative

Answer 1

Gram positive= thick peptidoglycan layer

Gram negative=thin peptidoglycan layer

Question 2

Gram stain appearance and shapes

Answer 2

Gram positive= purple
Gram negative= pink/red
Cocci= spherical
Bacilli= Rod shaped

Question 3

Describe the process of gram staining

Answer 3

Have culture, make smear
Spread on glass slide
Air dry and heat
Heating causes fixation, solution stick to glass slide
Add crystal violet to glass slide
All bacteria take up stain therefore turn purple
Add iodine which binds crystal violent trapping it in cell
Add acetone for decolorisation
Counter stain with safranin

Question 4

Why do gram positive bacteria turn purple vs gram negative

Answer 4

Gram positive thicker walls, less fatty acid so when washed with solvent, cell pores close means less permeable and are able to retain stain
Gram negative thinner more lipid cell wall, solvent washes out

Question 5

What 3 things are present on cell surface?

Answer 5

Plasma/cytoplasmic membrane
Penicillin binding proteins
Peptidoglycan/murein

Question 6

Structure/Role of peptidoglycan

Answer 6

strength, shape

carbohydrate polymers, cross lined with 3/5 amino acids

Question 7

Lipopolysaccharides

Answer 7

Elicit strong immune response in animal/human

component of gram negative cell wall

Question 8

Capsules

Answer 8

prevent phagocytosis

Question 9

Flagellum

Answer 9

Facilitate motility
Single tail- Vibrio cholerae,monotrichous
Multiple tails from single point- spirillum spp, Lophotrichous
Both sides- Rhodospirillum rubrum, amphitrichous
All over- Peritrichous

Question 10

Fimbriae

Answer 10

Adherence

Question 11

Spore forming bacteria

Answer 11

Divide by binary fission when nutrients available and good environment
Spore formation initiated when nutrients deficient and adverse environment
DNA condense, ailing in centre cell= mother cell
DNA divides into 2 copies, mother cell forms forespore,
mother cell membrane engulf developing spore
developing surrounded 2 membrane
peptidoglycan form cortex around developing spore
acid then forms and Ca+ enters spore and water removed
protein coat from exterior to cortex
spore now mature, resistant to environmental factors
mother cell broken down and spore released

Question 12

Plasmid

Answer 12

small circular double stranded DNA

involved with gene transfer, conjugation

Question 13

Conjugation

Answer 13

requires direct contact between donor and recipient cell
F+ carry F plasmid means make F pills and act as donor
F- have no plasmid
F plasmid makes F pillus which is protein appendage acts as bridge between donor and recipient
Contact between both cells and pilus binds with receptor sites on recipient
plasmid mobilized for transfer, cleaved and single strand beginning at origin of transfer enter recipient
Rolling circle mechanism duplicate one strand in donor
Complimentary strand synthesized in recipient cell
All cells become F+

Question 14

Binary fission

Answer 14

Identical progeny

Spontaneous mutation occur in any gene generation which causes genetic variation

Question 15

How can DNA be transferred?

Answer 15

Horizontal gene transfer
Transduction (occurs by virus)
Transformation (free flowing DNA captured by bacteria)

Question 16

Bacteriophage

Answer 16

Inject genetic material into pathogen
DNA take over machinery of bacteria and synthesize phages
Eventually burst bacteria
Known as lysis cycle

Question 17

How do you detect colonies of individual bacteria?

Answer 17

Culture on solid medium (agar)

Bacterial colonies seen by eye

Question 18

How do you detect individual bacteria?

Answer 18

Microscope

Staining (gram, fluorescent dyes)

Question 19

How is bacteria named?

Answer 19

genus and species