Antiseptics & Disinfectants Flashcards
What are some differences between Antiseptics & Disinfectants?
- Antiseptics can be used for dermal or mucous membrane application, whereas Disinfectants are applied to inanimate objects
- Antiseptics kill or inhibit the growth of micro-organisms, whereas Disinfectants only kill a range of micro-organisms
List some desirable properties of Antiseptics & Disinfectants
- Broad spectrum
- Not inactivated (by organic matters or different water conditions)
- Retain activity after rinsing
- Not induce resistance
- Not induce mutations
- Detergent property
- Odourless
- Colourless (no stains)
- Non-toxic
- Non-corrosive
- Economical
- Easy to use
What is the mechanism of action of Chlorhexidine
- Cell wall damage, alteration in cell membrane permeability
- Protein coagulation
- Enzyme inhibition and Denaturation
What is the mechanism of action of Halogen?
- Cell wall damage, alteration in cell membrane permeability
- Enzyme inhibition & denaturation
- DNA synthesis, replication and strand breakage
- Oxidative destruction
List 6 factors that affects the effectiveness of Antiseptics & Disinfectants
- Number and type of micro-organism
- Exposure time
- Exposure temperature
- Concentration of anti-microbial agent
- pH of treatment
- Presence of extraneous materials
Explain the ‘Death rate curve’
Log number of survivors (N(t)) vs. Exposure time (t)
At a constant temperature, the same percentage of organism is inactivated in each unit of time.
LogN(t) = LogN(0) - k.t
Slope = k = death rate constant
The steeper the slope, the higher the death rate constant, the more powerful the antibacterial treatment is.
Define “temperature coefficient” Q
The effect of temperature increase on the rate of inactivation.
E.g. If a disinfectant has Q(10) of 4, then 10°C increase in temperature will have a 4 fold reduction in time required to kill micro-organisms.
The higher the Q10 value, the more effect the temperature increase has on the reaction rate
Explain “Dilution Coefficient (n)”
A low dilution coefficient of a disinfectant indicates:
- the disinfectant is less affected by the dilution
- i.e. it is still effective at lower concentrations
What is the Dilution coefficient equation?
The effect of dilution on change in exposure time (t) can be calculated by:
t. c^n = k
t1. c1^n = t2. c2^n
t = time (min) required for killing c = concentration of the disinfectant n = dilution coefficient k = death rate constant
List 3 things that the pH can affect
1) Activity
2) Stability
3) Susceptibility
What is the effect of organic contaminants?
Blood, serum, pus, faeces, and fats can protect the micro-organisms from effective contact with disinfectants
- Inactivation or protection by these materials should be taken into account when determining the concentration of a disinfectant
What is MIC?
Minimum Inhibitory Concentration.
It’s the lowest concentration that inhibits the growth of micro-organisms (i.e. bacteriostatic concentration)
How do you test for the MIC of a disinfectant?
1) Disinfectant at various decreasing concentrations mixed with the nutrient broth in test tubes
2) Tubes are then innoculated with challenge micro-organisms and incubated to detect growth
3) Lowest concentration of disinfectant that shows no growth is defined as the MIC value
What is the Capacity test (Kelsey-Sykes)?
Test for ability to retain activity in the presence of increasing micro-organism load
Explain the ‘Phenol Coefficient test’ (Rideal-Walker)
It measures the bactericidal activity of a chemical compound in relation to phenol, with regards to its dilution factor under the same conditions.
Dilution factor of test disinfectant / Dilution factor of phenol
i.e. 1:20 dilution of disinfectant / 1:5 dilution of phenol = phenol coefficient of test disinfectant is 4.
What is the mechanism of Phenolic disinfectants
- Protein coagulation
- Cytoplasmic membrane leakage
List some properties of Phenolics (7)
- Not sporocidal
- High dilution coefficient
- Inactivated by dirty conditions
- More active at low pH
- Poor activity against Pseudomonas
- High Q(10) value
- Caustic
List some properties of Alcohols as a disinfectant (7)
- Alter cell membrane integrity
- Require water (e.g. 70% ethanol)
- Myco-bacterial
- Virucidal (except isopropanol)
- Non-sporicidal
- No dirt penetration
- Volatile
Name 1 sporicidal antiseptic/disinfectant
Aldehydes
List 2 problems with Aldehydes
Stability problems.
Toxicity problems.
How do Aldehydes exert their activity?
Cross-linking of cellular proteins
Alteration in DNA structure
What is the mechanism of Quaternary Ammonium Compounds?
Generalised cell membrane damage involving disruption of phospholipid bilayers
What’s one issue with Quaternary Ammonium Compounds?
Incompatible with anion agents
What can Chlorhexidine be used for?
Topical antiseptic.
Pre-op skin preparation (with alcohol)
