Microbiology

Question 1

How can medicines be contaminated

Answer 1

Personnel
Environment
Raw material (water)
Packaging
Use by patient

Question 2

Bacterial shape : cocci

Answer 2

Spherical
Single cells/ clusters/ in twos (diplococci)/ long chains

Question 3

Bacterial shale: rods or bacilli

Answer 3

Pairs or chains/ slightly curved/ curved
Spiral
Filaments

Question 4

Prokaryotic

Answer 4

Do not have membrane bound nucleus
Don’t have membrane bound organelles such as mitochondria

Question 5

Prokaryotic cell wall function

Answer 5

Maintains shape
Protection from osmotic lysis
Site of action of several important antibiotics

Question 6

What is the difference between gram negative and gram positive

Answer 6

Gram negative has an additional outer membrane layer

Question 7

Lipopolysaccharide

Answer 7

Only found in gram negative outer membrane
Present on external facing part of bilayer
Potential immune modulator= pyrogenic so raises body temperature during infection, causes septic shock
Very heat stable and not destroyed by moist heat sterilisation

Question 8

Acid fast bacilli/ mycobacterium

Answer 8

Gram positive organisms with additional long chain ‘waxy’ mycolic acids in cell wall
Contributes to resistance to many disinfectants and antibiotics

Question 9

Generation time in bacterial population growth

Answer 9

Time it takes for cell number to double
Constant

Question 10

Stationary phase of bacterial growth curve

Answer 10

Balance of cell death and cell division
There is nutrient limitation and accumulation of toxic waste

Question 11

Bacterial endospores

Answer 11

Triggered by lack of nutrients
Special coating around the cells for protection
Allows to survive for long periods
Germinate when conditions are favourable

Question 12

Calculating population size during log phase

Answer 12

Nt = No 2^n

Nt= number of cells after a given time t
No= number of cells present initially
n= number of generations in time t

Question 13

Bacterial growth requirements

Answer 13

Culture media
Oxygen requirement
Temperature

Question 14

Culture media

Answer 14

Defined media= all components known
Complex media= peptones, meat/yeast extracts
Selective media = favour growth of particular microorganisms
Differential media= distinguish between bacterial and sometimes permit identification

Question 15

Oxygen requirements

Answer 15

Obligate aerobes require oxygen (for glycolysis, metabolism)
Facultative anaerobes can survive with or without oxygen
Obligate anaerobes are inhibited by oxygen

Question 16

Temperature

Answer 16

Most bacterial grow optimally at 37
Thermophiles= hot, sometimes greater than 100
Psychrophiles= fridge, cold temp

Question 17

Identification of unknown bacteria

Answer 17

Colony morphology = shapes of colonies
Selective media= clues about conditions they need to grow
Gram stain
Growth in air= anaerobes or aerobe
Biochemical tests= metabolisms

Question 18

Staphylococcus aureus

Answer 18

Gram positive
Very common hospital acquired pathogens
Huge range of infections= skin infections, UTI

Question 19

Escherichia coli

Answer 19

Gram negative
Small component of gut bacteria
Large range of infections= uti, gastrointestinal

Question 20

Pseudomonas aeruginosa

Answer 20

Gram negative
Can survive and multiply in simple aq environment (sinks, shower heads , aq pharmaceuticals)
Very resistant to many antimicrobials
cause of serious infections= serious eye infections=blindness, wound/chest infections particularly in burn patients