Bacteriology: structure, function, classification

Question 1

What are prokaryotes?

Answer 1

• archaea
• bacteria

Question 2

What are eukaryotes?

Answer 2

• eucarya
• (nucleated, organelles)

Question 3

What are some examples of distinguishing features of bacteria?

Answer 3

• morphology
  
  • microscopy
  • colony
• staining characteristics (gram)
• growth requirements
• toxin and enzyme production
• response to phages or antimicrobials
• presence/ absence of surface/ antigenic structures

Question 4

How do bacteria replicate?

Answer 4

• binary fission
• haploid
• DNA is replicated
• then the cell membrane is elongated and the 2 DNA molecules separated
• cell wall forms and cell membrane invaginates
• cross wall forms completely
• then get 2 daughter cells

Question 5

What are the different phases in the growth curve?

Answer 5

• lag phase - preparing for the exponential growth
• log phase - bacteria divide as quickly as they can
• stationary phase - growth is equal to death - nutrients are depleting
• death phase - die due to no nutrients left/ oxygen used up
• long-term stationary - not all die

Question 6

What are the categories of bacteria?

Answer 6

• bacilli - rods
• cocci - spherical
  
  • staphylococci - bunch of grapes
  • streptococci - long line
• spirochaetes
• vibrios - comma

Question 7

Answer 7

Question 8

How are endospores formed?

Answer 8

• DNA replication in vegetative cell
• DNA lines up along long axis
• cell membrane invaginates inside to form forespore
• the cell membrane grows and engulfs the forespore in a secondary membrane
• vegetative DNA disintergrates
• a cortex of calcium and diplicolinic acid is deposited between membranes
• spore coat forms around endospore
• maturation of endospore - completion of spore coat - increased resistance to heat etc.
• endospore released from cell

Question 9

What are the different bacteria staining techniques?

Answer 9

• Gram staining
  
  • +ve/-ve
  • based to crystal violet staining and counterstaining
  • heat fixation
• Diff Quick
  
  • rapid - morphology
  • wet fixation
• Specific
  
  • ZN - mycobacteria
  • silver - spirochaetes

Question 10

How is gram staining done?

Answer 10

• heat fixation
• crystal violet - stains everything (peptidoglycan)
• iodine - traps the cv in cell - stays in the gram +ve cells
• alcohol wash - washes cv out of gram -ve cells - but it is trapped in the gram +ve due to iodine
• safranin - counterstaining - gram -ve = pink, gram +ve = purple

Question 11

Why is staining different between gram +ve and -ve?

Answer 11

• gram +ve- have thick peptidoglycan layer and a single cell membrane - peptidoglycan binds cystal violet
• gram -ve - inner and outer protective membrane, thick peptidoglycan layer - no trapping of cv to peptidoglycan

Question 12

Role of peptidoglycan?

Answer 12

• gives rigidity to bacterial cell
• assists in preventing phagocytosis
• pyrogenic properties (fever)
• degraded by lysozyme

Question 13

How to do Diff quick staining?

Answer 13

• one drop on slide - allow to air dry briefly
• place in fixative
• solution 1
• solution 2
• distilled water wash

Question 14

What are the different types of growth media?

Answer 14

• nutrient media (slower growth)
  
  • nutrient agar
  • Mueller Hinton
• enriched media - fastidious organisms
  
  • blood/ serum agar (whole blood, lysed blood, serum)
  • electron acdeptors, energy sources
• selective media
  
  • supplemented plates e.g. antibiotics (camp)
• differential use of nutrients (fermentation of sugars)
  
  • MacConkey agar

Question 15

Name the gas conditions

Answer 15

• oxygen
  
  • aerobic
  • facultative anaerobic - survive in both but sometimes will need electron acceptors to survive without oxygen
  • microaerobic - camp
• co2
  
  • all organisms
  • capnophiles - >5%
• hydrogen

Question 16

What are the optimal temps for listeria and thermophilic campylobacter spp?

Answer 16

• 4 degrees
• 42 degrees

Question 17

What is the oxidase test? which bacterium are +ve/ -ve?

Answer 17

• testing for gram -ve bacteria
• based on cytochrome C oxidase
• +ve = moraxella, Neisseria, Campy, Pseudomonas = dark purple
• -ve = Enterobacteriaceae = stay white/ yellow

Question 18

What is the catalase test?

Answer 18

• tests the conversion from H2O2 to H2O and O2
• bubbles
• +ve = staphylococcus, listeria, enterobacteriaceae
• -ve = streptococcus, enterococcus

Question 19

What is the coagulase test?

Answer 19

• tests conversion of fibrinogen to fibrin
• see if insoluble material formed - if so +ve
• +ve = s.aureus, s.intermedius
• -ve = s. epidermis, s.hominis (CNS)

Question 20

What is an API strip?

Answer 20

• enzymes and substrates
• multiple biochemical tests at once

Question 21

What is MacConkey agar?

Answer 21

• selects for lactose fermenters
• senses pH - change with neutral red
• inhibits gram +ve growth with bile and cv
• if lactose fermenting = pink/red e.g. E.coli
• if not = yellow e.g. salmonella

Question 22

How do you plate out?

Answer 22

• flame the loop

Question 23

What are the different types of hemolysis?

Answer 23

• beta = complete
• alpha = partial
• gamma = none

Question 24

What are the other typing methods used?

Answer 24

• hemolysis - may be host specific
• serology - based on antisera to surface structures
  
  • flagella
  • LPS/ LOS
  • capsule
• phage -typing - susceptibility to panel of bacteriophages
• antimicrobial resistance

Question 25

What steps are taken in initial diagnostics?

Answer 25

* microscopy * culture * antigen/ molecular tests/ typing