Different classes of antimicrobials

Question 1

Bacteriostatic

Answer 1

Cells stop dividing but remaining viable

Question 2

Bacteriocidal

Answer 2

Cells are killed but dead cells remain

Question 3

Bacteriolytic

Answer 3

Cells are killed + broken down

Question 4

Minimum bactericidal concentration (MBC)

Answer 4

Lowest concentration of antimicrobial agent/drug that kills 99.9% of the given test organism

Question 5

Minimum inhibitory concentration (MIC)

Answer 5

Highest dilution/Lowest concentration of the antibiotic that inhibits overnight visible growth

Question 6

What are the 3 non-antibiotic antimicrobials?

Answer 6

Antiseptics, Disinfectants + Preservatives

Question 7

Antiseptics

Answer 7

• Against Sepsis
• Destruct/inhibit microorganisms on living tissues
• Non-toxic to host
• For ex-vivo (wounds, mouth)

Question 8

Disinfectants

Answer 8

• Remove microorganisms from inanimate objects/surfaces
• Kill/reduce number to an acceptable level
• They can have different levels of action
• They can be too toxic on body tissues
• Known as germicides/sterilants

Question 9

Preservatives

Answer 9

• Added to pharmaceutical, food, cosmetics to prevent spoilage
• Non-toxic to humans
• Low antimicrobial effect ‘at use’ concentration
• Levels of activity lower than disinfectants/antiseptics
• British Pharmacoepoeia states that it must be effective against 2 bacteria, yeast + mould

Question 10

How do you choose the right Biocide?

Answer 10

• Know likely risk + microorganism
• Type of microorganism present + contamination levels have huge effect on the outcome of treatment
• Efficacy of antimicrobial agent must be simulated tests to guide biocide choice

Question 11

Factors affecting Biocide choice

Answer 11

• Biocide properties
• Microbial challenge
• Intended application
• Environmental factors
• Toxicity of agent

Question 12

Classes of Resistance

Answer 12

Intrinsic + Acquired

Question 13

Which bacterium is more resistant to BIOCIDES + why?

Answer 13

Gram-negative

• Outer membrane can affect adsorption + uptake
• High number of phosphate groups in the Lipid A region of LPS increases

Question 14

What influences antimicrobial activity of biocides?

Answer 14

Affinity of the biocide to the microbial cell

Question 15

What is affinity influenced by? Give example

Answer 15

Environmental factors

• pH influences ionic state of cell membrane
• Higher pH = More electronegative the cell surface which makes biocides more effective

Question 16

Entry of biocide into cell

Answer 16

• adsorb to cell surface + interact with outer layers using electrostatic/hydrophobic interactions
• uptake into cell via porin channels or diffusion + interact with target proteins, enzymes + nucleic acids
• cell death
  biocides exert aa. thru structural damage of cell wall using cellular components

Question 17

Antibiotic

Answer 17

• systemic antimicrobial (infections in the body)
• low host toxicity
• targeted selective toxicity
• natural + synthetic
• bacteriostatic + bacteriocidal

Question 18

strength of toxicity between antibiotic + non-antibiotic antimicrobials

Answer 18

Antibiotics have a low host toxicity but its toxicity is targeted + selective
Non-antibiotic antimicrobials have a high host toxicity as well as broad + non-selective

Question 19

Bacteria can become resistant to biocides. What are the classes of resistance:

Answer 19

Intrinsic (natural) + acquired (by mutation)
- gram-negative is more often resistant due to outer membrane (affecting absorption) + high number of phosphate groups in the lipid A region of LPS increases

Question 20

BP pharmacopoeia state that preservatives have to be effective against

Answer 20

2 bacteria, yeast + mould

Question 21

Non-antibiotic antimicrobial

Answer 21

Ex-vivo use only
High host toxicity
Broad, non-selective toxicty
Chemical agents classed as biocides
Bacteriostatic, -cidal + -lytic