Lesson 1: Bacterial structure, growth, enumeration and identification

Question 1

Gram positive bacteria

Answer 1

• More peptidoglycan than -ve, contains technoic acid and has no liposaccharides and less proteins

Question 1

Gram negative bacteria

Answer 1

• Cell envelope can produce symptoms of disease (endotoxins)
• Rod shaped (bacilli) or spherical (cocci)
• Has a complex structure
• Outer membrane compromised of lipopolysaccharides
• Contains more proteins and lipid than +ve

Question 2

Features of the cytoplasmic membrane

Answer 2

• Semi-permeable (only low Mr pass)
• Contains vomit pumps
• Many proteins and enzymes for bacterial survival
• Target to many antibiotics

Question 3

Ribosomes

Answer 3

70s ribosomes made up of ribosomal protein and ribosomal RNA.

Question 4

Flagellum

Answer 4

Bacterium mobility

Question 5

Pilli (fimbrae)

Answer 5

Fine hair like filaments that are sneaker than flagella

Question 6

Types of function for pilli

Answer 6

Adherence- attatchment
Antigenic- Chemotaxis
Genetic exchange- virulence: toxins

Question 7

How does binary fission happen?

Answer 7

• Increase of cell mass
• Duplication of genome
• Cell membrane and cell wall separation

Question 8

How is bacterial growth measured and what does the growth diagram tell us?

Answer 8

It is measured in change in population rather than mass or size, the diagram shows us lag phase, growth phase, stationary phase and death phase.

Question 9

What is formula used to tell us the total population at the end of a giving period (starting with 1 cell)

Answer 9

b = 1x2^n
n is number of generations

Question 10

Chemical requirements for growth

Answer 10

• Energy source
• Source of electrons
• Carbon source
• Nitrogen source
• Oxygen, sulphur and phosphorous
• Ions

Question 11

Physical requirements for growth

Answer 11

Optimum:
- Temperature (depends on type of bacterium)
- pH 6.5-7.5

Question 12

Preventing growth using pH

Answer 12

• extreme pH prevent microbial growth
• neutral pH: bacterial spoilage
• pH>8: rare spoilage (soap based emulsion)
• low pH: spoilage by moulds and yeast e.g fruit juice flavoured syrups

Question 13

Water Activity

Answer 13

Water activity of aqueous formulations can be lowered to decrease microbial growth

Question 14

What do sterile pharmaceutical products need to be ?

Answer 14

• sterile on dosage form and other preparations labelled sterile
• needs to comply with test for sterility

Question 15

Non sterile pharmaceutical products

Answer 15

• prep for topical use, use in resp tract, oral and rectal administration + containing raw materials
• herbal remedies

Question 16

Enumeration/Colony count

Answer 16

Single bacterium in OG culture is plated to give rise to a viable colony counted in cfu

Question 17

What are some plate count methods?

Answer 17

• pour plate
• spread plate

Question 18

Where can contamination or bacterial growth happen?

Answer 18

• Cosmetics
• Emulsion
• Trans-parenteral nutrition bag

Question 19

Why is rRNA important in classification?

Answer 19

It’s present in all living celss and its sequence forms basis pf phylogeny (study of evolution of organisms)

Question 20

Traditional methods of bacterial identification

Answer 20

• Cultivation- growth requirement
• Cultivation- selective agar
  -Biochemical profiling
• Serological testing

Question 21

Advantages of tradiitonal bacterial identification methods

Answer 21

• No specialised equipment
• Can be done by most laboratories
• Minimal training

Question 22

Disadvantage of traditional bacterial identification methods

Answer 22

• 24-72 h for results

Question 23

Advantage of newer bacterial identification methods

Answer 23

• Faster -6hrs
• Some have low running costs (e.g
  MALDI-TOF MS)
• More samples required so more accurate

Question 24

Disadvantage of newer bacterial identification methods

Answer 24

• Specialised equipment required (£)

Question 25

What happens is gram positive bacteria in gram staining tests?

Answer 25

They remain blue because of its low lipid content (which lipid is needed for retention of iodine crystal violet complex)

Question 26

What happens to gram negative bacteria in staining tests?

Answer 26

It turns colourless because of its high lipid concentration in cell wall outer layers which facilitates release of iodine crystal violet complex leaving cell colourless.

Question 27

Staph aur structure

Answer 27

Gram positive, facultative anaerobe, catalase-positive cocci

Question 28

E.coli structure

Answer 28

Gram negative enetric rod, faculative anaerobe, pink in MAC agar

Question 29

Pseudonomoas

Answer 29

Gram negative rod

Question 30

What is a facultative anaerobe?

Answer 30

makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent.