bacteria structure and function

Question 1

what is the general structure of bacteria

Answer 1

1. flaggellum- movement
2. pilli- adhesion- sticking
3. capsule
   4.peptidoglycan cell wall
4. plasmid and circular DNA

Question 2

what is 3 features of bacteria

Answer 2

• prokaryotic
• single celled
• no membrane bound organelles

Question 3

where is bacteria found in are body

Answer 3

• sterile areas- cause disease examples include blood, urinary tract, brain, eyes
• non sterile areas- does not cause disease and can be commensals e.g. gut, mouth, skin

Question 4

how do bacteria cause disease

Answer 4

• colonise
• invade
  -multiply
• cause host cell damage

Question 5

what are examples of gram positive bacteria

Answer 5

• streptococcus pyogenes
• streptococcus pneumonia
• streptococcus agalactiae
• staphylococcus aureus
  -staphylococcus epidermidis

Question 6

are gram positive bacteria tend to be cocci or bacilli

Answer 6

coccus

Question 7

are gram negative bacteria tend to be bacilli or coccus

Answer 7

bacilli

Question 8

how to distinguish between gram negative and gram positive bacteria

Answer 8

• stain bacteria with crystal violet this maes all bacteria purple
• than add iodine
• than add ethanol- this washes out the dye in gram negative bacteria to make it colourless
• add safron this dyes the colourless gram negative bacteria pink
• so at the end of the stain if purple= gram positive and if pink=gram negative

Question 9

why does gram positive stay purple

Answer 9

thick peptidogylcan wall so dye doesnt wash out with ethanol

Question 10

what are some organisms which cannot be stained with gram stain

Answer 10

mycoplasma, chlamydia, legionella
these have no cell wall

Question 11

what is mycobacterium and what is it stained with
give example of mycobacterium

Answer 11

• mycobacterium tuberculosis
• is not gram positive nor gram negative has a waxy cell wall made of mycolic acid
  -stained with neihl zeelson staining

Question 12

how can you distinguish between the different streptococcus

Answer 12

• do a blood haemolysis test
• if bacterium fully digest blood it is beta haemolytic e.g. s. pyogenes and s. agalactiae
• if bacterium partially digests blood it is alpha haemolytic and could be s. pneumonia

Question 13

how to distinguish between s. pyogenes and s. agalactiae

Answer 13

• lancefield testing
• s.pyogenes group A strep
• s. agalactiae- group B strep

Question 14

how to distinguish wether a alpha haemolytic streptococcus is s. pneuomonia or not

Answer 14

• optochin (antibiotic) sensitivity test
• if sensitive it is s.pneumoniae
• if it is not sensitive it is not s. pneumoniae (clinically insignificant)

Question 15

how to distinguish between s. aureus and s. epidermidis

Answer 15

• coagulase test
• s. aureus coagulation would occur
• s. epidermidis coagulation would not occur
• s. aureus more clinically significant- dangerous
• s. epidermidis- lives on skin as commensal

Question 16

what are the different shapes of bacteria

Answer 16

• bacilli (rods)
• cocci (circles)
  -cocco-bacilli (ovals)
• vibriae (curved rods)
• spirochaetes (spirals)

Question 17

what are examples of gram negative bacteria

Answer 17

E.coli
salmonella
neisseria meningitidis (diplo cocci)
neisseria gonnorhoae (diplo cocci)

Question 18

why is mycoplasma not stained and give example of of a mycoplasma

Answer 18

• has no cell wall= no staining
• mycoplasma pneumoniae
• tiny intracellular organisms

Question 19

where are gram negative bacteria mainly found

Answer 19

• urinary
• meningitis
  -intra-abdominal

Question 20

where are gram positive bacteria usually found

Answer 20

• respiratory
  -skin
• bone and joint
• meningitis

Question 21

what are the phases in growth of a bacteria colony

Answer 21

• lag phase (no increase )
• logarithmic phase (exponential growth- unlimited resources no competition replication occurs via binary fission)
• stationary phase - competition for nutrient and space
• death phase- decline in population