IC7 Evaluation of Disinfectant Activity Flashcards
Properties of ideal disinfectant (12)
- Broad spectrum
- Fast acting
- Non toxic
- Odourless
- Economical
- Water soluble
- Stable
- Good cleaning properties
- Environmentally friendly
- Not affected by environmental factors
- Surface compatibility
- Leave antimicrobial film on treated surface
Bacterial growth process
- Binary fission
- Lag phase: cells not dormant but they are starting all the process for cell replication like synthesis of RNA or enzymes
- Log/exponential phase: cells are doubling at constant rate, slope indicate speed of process. Take hours-days to grow
- Stationary phase: growth-limiting factors affect replication, making growth and death rate comparable. No more material for cells to reproduce. Waste material accumulates
- Death phase: rate similar to log phase
Kinetic parameters (3)
- Rate constants: equation indicates the changes of microbial populations as a function of time
- Temperature coefficients: influence of temperature on microbial population inactivation
- Electric field: intensity applied should be above the threshold electric field intensity, which is the critical electric field intensity for target microorganism
What is the procedure to evaluate disinfectant activity? (7)
- Preparation of carriers (stainless steel)
- Preparation of test organism and inoculum (different strain used, different result)
- Inoculation, drying (affect microbial load) and transfer of carriers
- Exposure of dried inoculum to test substance or control fluid (standardise carrier, fixed area)
- Neutralisation of test substance (remove disinfectant) and elution of test organism (regrow bacteria for proper counting then back counting of initial bacterial load)
- Dilution and recovery of test organism
- Counting the surviving test organisms and assessing the performance of test substance (imageJ)
Define Minimum inhibitory Concentration (MIC)
The lowest concentration of an antimicrobial agent that inhibits growth, as determined visually after a standard incubation period (usually 18 to 24h)
MIC = lowest concentration of antimicrobial that prevents visible growth of an organism (Cteng definition)
Define minimum recommended concentration (MRC)
A concentration that takes into account possible mistakes that can be made during use of disinfectant (ensures disinfectant is still able to carry out function despite mistakes); usually stated by manufacturer
Define minimum effective concentration (MEC)
the lowest concentration of active ingredients at which the product is still effective
Define minimum bactericidal concentration (MBC)
The lowest concentration of an antibacterial agent that causes at least a 3 log reduction in the number of surviving cells (compared with the initial, preincubation concentration) after incubation
Define minimum selective concentration (MSC)
Minimum concentration of antimicrobial agent at which resistant strains have a competitive advantage (bacteria becomes more resistant to the disinfectant)
What are the differences between hygienic handrub and hygienic handwash?
Hygienic Handrub:
- Refers to treatment of hands with an antiseptic handrub
- Antiseptic is broad spectrum and fast‐acting, persistent activity is not necessary.
Hygienic Handwash:
- Refers to treatment of hands with an antiseptic handwash and water
- Broad spectrum, but is usually less efficacious and acts more slowly than the hygienic handrub
It is possible to directly compare tests for hygienic handrub/handwash. True or False?
False.
Many variation in protocols may exist between tests (e.g Contamination of hand with a test organism before test, To contaminate fingers or hands, The volume of hand hygiene product applied, Contact time)
The purpose of hygienic handrub/wash is to reduce all flora from the hand surface. True or false?
False. Purpose is to reduce the transient flora without necessarily affecting the resident skin flora
what are the classification of type of evaluation test? (3)
- based on organisms
- based on test (suspension or carrier)
- based on standard use
What is the difference between 1 step method and 2 step method when it comes to disinfection testing (use of interfering substance)?
1 step method to test efficacy of disinfectant is used when interfering substance is NOT desired:
- In 1 step method, disinfectant is added to aqueous solution of bacteria and water (a mixture of bacteria and water). Gives less information but gives idea of what is the potency of disinfectant and if microorganism is resistant
Disinfectant is tested on a carrier using 2 step method (more common):
- In 2 Step method, the bacteria and the dirt the ‘interfering substance’ are dried on to stainless steel discs, and the disinfectant is tested to try and reduce bacterial numbers
What is frequently used as an interfering substance?
protein from cow serum
