IC7 Disinfection Process Flashcards
What are 2 characteristics of disinfectants used to eliminate microbes?
- Physical aspect (Cleaning)
- Biological aspect (Antimicrobial)
What makes an ideal disinfectant? List 12 properties
- Broad spectrum antimicrobial coverage
- Rapid acting - Quick onset
- Not affected by organic matter and detergents / chemicals
- Non-toxic to patient
- Surface compatibility (Metal, plastic, rubber deterioration or corrosion)
- Residual effect - Antimicrobial film
- Odorless
- Economical
- Soluble in water
- Stable in concentrate and use-dilution
- Cleaning properties
- Environmentally friendly
What factors affect disinfectant activity?
- Disinfectant agent properties
- Microorganism nature, physiologic state, microbial communities, biofilm, resistance
- Physicochemical Environment - Temperature, Organic matter, Electrolytes
What is bacterial growth called? How is it determined?
What are the four phases of bacterial growth? What happens at each phase?
Binary fission - Growth is shown as CFU (Colony forming units) against Time
By laser scatter spectrometry or observe turbidity
Phases:
1. Lag phase - Dormant, synthesis of materials (RNA synthesis & enzyme activity)
- Log / Exponential phase - Hours to days of replication, splitting into daughter cells (Doubling at constant rate) Note: Not all daughter cells survive though.
- Stationary phase - Growth rate = Death rate due to growth-limiting factors (e.g. no more nutrients for cells to reproduce, waste accumulation)
- Death phase
What kinetic parameters do we use to compare different processing technologies for the reduction of microbial populations?
- Rate constant = Change in microbe population as a function of time given that conditions remain constant
- Temperature Coefficients = How temperature affects microbial inactivation (also depending on pathogenic thermal resistance)
- Electric Field Constants = The critical electric field intensity for target
What factors have the most effect on efficacy?
Contact Time - Duration of exposure
Others: Concentration & Potency, Biofilms
What are the 7 steps for evaluating disinfectant activity?
- Prepare carrier (Stainless steel)
- Prepare test organism & inoculum
- Inoculation, Dry, Transfer to Carrier
- Expose Dried Inoculum to Test substance / Control fluid
- Neutralize test substance + Elute Test organism
- Dilution + Recover Test organism
- Count surviving test organism + Assess Disinfectant activity
What are 6 considerations in each step of the 7-step disinfectant evaluation test?
Step 2 & 4 - Representativeness & reliability of test strain (What strain are we testing? Why are we testing this strain?);
Inoculum preparation (What is the population of microorganisms introduced in the fermentation medium?)
Step 5 - Neutralize and wash by membrane filtration (How should I remove my disinfect test substance?)
Step 6 - Quantitative recovery of microorganisms (How can I ensure a specific constant recovery rate using the contact plate?)
Step 7 - Criteria for activity (How do you measure disinfectant activity? What does the criteria depend on?);
Counting of survivors (How can I calculate the original microbial load?)
Sample Size (Standard comparison)
Revival of survivors (Assess growth medium before the testing)
What would you include as your test strain for disinfection evaluation testing?
The most common strain is selected as it is most representative
What variables are kept constant (independent variable) and what variables can be changed to test disinfectant activity on a test strain?
How is disinfectant activity interpreted?
Constant - Exposure time
Changed - Add interfering substance to simulate practical conditions (2 step method - 1. Aqueous suspension Bacteria & Water, 2. Bacteria & Dirt)
Interpretation criteria - 4 to 6 Log reduction to test efficacy
How do we determine the criteria for disinfectant activity?
The Setting
MIC - Test the minimum bacteriostatic activity (Inhibitory)
MEC - Test the minimum bactericidal activity (Effective)
MRC - Manufacture recommendation, taking into account that dilution & cleaning are not good
MBC - 4 Log reduction (Bactericidal)
MSC - Selective strain
What are 3 types of tests for the one-step method?
Suspension test
Carrier test
In-use / Field test
What is the procedure for suspension test?
Mix fixed volumes of known dilutions of disinfectant with fixed volume of inoculum
What is the procedure for carrier test?
- Disinfectant directly dropped on carrier surface at room temperature
- Carrier immersed in disinfectant dilution
- Disinfectant dispersed by spray or aerosol
What are 4 tests based on standards?
AOAC test = Stainless steel carrier soaked in bacteria + Treat with disinfectant
AFNOR test = Sample plate sprayed with disinfectant + Test germs application
DGHM = Dirty surfaces exposed to disinfectant -> Then plate out on nutrient agar
Dutch standard suspension test (EN13727) = Test sample in bacterial suspension + Interfering substance
