properties of ideal disinfectant
1) broad spectrum
2) fast acting
3) not affected by environmental factors
- active in presence of organic matter
- compatible w soap, detergent, other chemicals
4) nontoxic
5) surface compatibility
- X corrode instrument & metallic surface
- X deteriorate cloth/rubber/plastic/other material
6) residual effect on treated surface
7) odourless/pleasant odour
8) economical
9) soluble in water (easier to wash away)
10) stabile in concentration & use dilution
11) good cleaning properties
12) environmental friendly on disposal
factors affecting activity of disinfectant - microorganism related
1) nature of microorganism
2) physiologic state of microorganism
3) microbial communities & biofilm
- different strains of bacteria from biofilms -> too selective disinfectant = not effective
4) natural & acquired resistance
- if resistant to 1 type means resistant to other disinfectant with same MOA
factors affecting activity of disinfectant - environment
1) conc
2) temp
3) presence of organic matter
4) electrolytes
5) Additives & excipients
phases of bacterial growth
1) lag phase
- cells not dormant
- processes to prepare for cell replication
2) exponential phase
- cells double at constant rate
3) stationary phase
- growth-limiting factors affect replication
- equilibrium: death = growth
4) death phase
- growth limiting factors = limited resources = die
what can you tell from the phases of bacteria growth
can tell the disinfectant’s MOA base on which phase it is effective in
kinetic parameters in inactivation of microorganism
1) rate constant
2) temperature coefficient
3) electric field (RARE)
factors interfering w evaluation tests & criteria for activity - general list
1) test strains
2) Criteria for activity
3) critical point in test method
4) quantitative recovery of microorganism
5) size of sampling
6) subculture & revival of survivor
factors interfering w evaluation tests & criteria for activity - criteria for activity
1) minimum inhibitory constant (MIC)
- lowest concentration that inhibit growth buy won’t kill
2) minimum effective constant (MEC)
- lowest concentration where product is effective
- bacteriostatic & bactericidal
3) minimum recommended concentration
- common practice instead of MIC/MEC (cuz MIC/MEC X account interfering factors)\
4) minimum bactericidal concentration
- X commonly used
- concentration that should reduce bioburden by factor of 1000
5) minimum selective concentration (MSC)
- min effective concentration against a few strains but not all strains of bacteria
factors interfering w evaluation tests & criteria for activity - critical point in test method
- preparation of inoculum
- neutralisation/washing by membrane filtration
- detection & count of survivor
factors interfering w evaluation tests & criteria for activity - subculture & revival of survivor
time, temp, humidity, pH
what is inoculum
population of microorganisms/cells introduced in fermentation medium/other suitable medium
inoculum development process
- taken from working stock culture to initiate growth in suitable liquid medium
- bacterial vegetative cell/spores:
** suspended in sterile tap water/saline
** added to broth - fungi & actinomycytes
** hyphae used for inoculum
why development of inoculum done in sequential steps?
increase volume of initial inoculum to desired level
equation for colony forming unit (CFU)
CFU = (colonies x dilution factor) / volume of culture plate
disinfection test vs antimicrobial agent evaluation
- disinfection test X use MIC
- disinfection test have different mechanism & activity = non linear killing curve (measures how much time it takes for disinfectant to work)
- disinfection test measure inhibitory effect & post exposure effect
test parameters for disinfectant test - got how many
1) exposure time
2) interfering substance
3) interpretation criteria
test parameters - exposure time
- how long to use disinfectant
test parameters - interfering substance
- stimulates practical condition
- 2 step methods:
1) aq suspension (bacteria + water)
2) bacteria + interfering substance dried on stainless steel disc -> add disinfectant
factors interfering w evaluation tests & criteria for activity - interpretation criteria
- log reduction in certain amount of time!!
- important to know amt of microbes at the start (baseline vibes)
- if 1 population = 1 million,
** 1 log reduction = 10% left, kill 90%
** 2 log reduction = 1% left, kill 99% - ideally > 4 log reduction for the tests!
why is sample size important?
reliability of results
why do you need substance/interfering material ratio?
determine effect of interfering material because it affects different disinfectants to different extents
what is the point of initial titer of virus
to be sure that calculation of reduction rates are correct
why neutralisation
removing/neutralising disinfectant so regrowth not affected
what is the role of incubation
achieve proper quantitation
