Different classes of antimicrobials Flashcards
Bacteriostatic
Cells stop dividing but remaining viable
Bacteriocidal
Cells are killed but dead cells remain
Bacteriolytic
Cells are killed + broken down
Minimum bactericidal concentration (MBC)
Lowest concentration of antimicrobial agent/drug that kills 99.9% of the given test organism
Minimum inhibitory concentration (MIC)
Highest dilution/Lowest concentration of the antibiotic that inhibits overnight visible growth
What are the 3 non-antibiotic antimicrobials?
Antiseptics, Disinfectants + Preservatives
Antiseptics
- Against Sepsis
- Destruct/inhibit microorganisms on living tissues
- Non-toxic to host
- For ex-vivo (wounds, mouth)
Disinfectants
- 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
Preservatives
- 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
How do you choose the right Biocide?
- 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
Factors affecting Biocide choice
- Biocide properties
- Microbial challenge
- Intended application
- Environmental factors
- Toxicity of agent
Classes of Resistance
Intrinsic + Acquired
Which bacterium is more resistant to BIOCIDES + why?
Gram-negative
- Outer membrane can affect adsorption + uptake
- High number of phosphate groups in the Lipid A region of LPS increases
What influences antimicrobial activity of biocides?
Affinity of the biocide to the microbial cell
What is affinity influenced by? Give example
Environmental factors
- pH influences ionic state of cell membrane
- Higher pH = More electronegative the cell surface which makes biocides more effective
Entry of biocide into cell
- 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
Antibiotic
- systemic antimicrobial (infections in the body)
- low host toxicity
- targeted selective toxicity
- natural + synthetic
- bacteriostatic + bacteriocidal
strength of toxicity between antibiotic + non-antibiotic antimicrobials
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
Bacteria can become resistant to biocides. What are the classes of resistance:
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
BP pharmacopoeia state that preservatives have to be effective against
2 bacteria, yeast + mould
Non-antibiotic antimicrobial
Ex-vivo use only High host toxicity Broad, non-selective toxicty Chemical agents classed as biocides Bacteriostatic, -cidal + -lytic
