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.
