Biocides and Disinfection L19 Flashcards
what did Pasteurs ‘germ theory’ lead to
washing hands before surgery
heat sterilisation of surgical instruments
carbolic spray into atmosphere to try reduce bacteria in atmosphere
what is an antimicrobial agent
Chemicals agents used to Kill or Inhibit growth of microbes
what is sterile
absolute term
No living organisms present. Even if there is one cell is not sterile
what do disinfectants and antiseptics kill
only vegetative cells
what do sanitizers do
kill only 99.9% of vegetative cells: reduce the microbial load to a safe level=
what is a bacterostatic antimicrobial antibiotics for
designed to inhibit bacteria
what is mycostatic antimicrobial agents for
designed to inhibit moulds
what happens in mould inhibition
inhibiting germination of moulds from the spores, will not necessarily inactivate the spore, but prevent outgrowth
what is fungistatic antimicrobial agents for
designed to inhibit fungi
where are fungistatics
usually on plants
what are fungistatics used for
crop production
what is sporocidal chemicals
particular chemicals that are targeted at those endospores
which spore is most and least robust
Fungal spores are generally less robust
Bacterial spores have particular robust structure that needs particular chemicals –sporicidal
why is antimicrobial agent virucidal not viralstatic
nothing top be static about as viruses are inert until they’re in the host cell
what is autoclaving
Temperature of boiling water increased by heating under pressure
what is used in autoclaving
Wet heat (steam) is more penetrative and causes denaturation of macromolecules in cell Especially proteins
what are the standard conditions in autoclaving
15 lbs/in2 at 121°C for 15-20 min
15 pounds/square inch
what is autoclaving the same as
domestic pressure cooker
what method scan be used to assess biocide activity
simple disk-diffusion method
quantitative suspension tests
what is simple disk-diffusion method
Paper disk soaked in test chemical is placed on a lawn of the test organism
Plates are incubated to identify any zones of killing
what is efficacy proportional to in simple disk-diffusion method
Efficacy is proportional to the zone size
what is the simple disk-diffusion method show
Want to know how effect the chemical is on certain microbes
in simple disk-diffusion what does a big zone of inhibition mean
bigger then inhibition zone ring the lower concentration that will kill your organism – sensitive to lower concentrations
what happens in the simple disk-diffusion method
Concentration of whatever youre looking at on the disk but it will diffuse out into the agar as the agar is wet, so have a chemical gradient, with highest conc in centre of the disk getting lower as go out into the zone of inhibition
what happens in quantitative suspension tests
Another way is to quantify the killing
Take a set number of cells and mix it with test chemical, incubate (often for long periods of time) look at the log reduction by preparing the serial dilutions and plating them out then counting the survivors
what is the D value
time to destroy 90% of the starting population for a given concentration of biocide
what is a 1 log10 drop
100 –> 10
90% of cells killed
how can cells be killed in D value
heat
biocides
what must we think about when picking a disinfection etc
Need to think about the amount of microbes that are present on the surface at the start to see what will be effective
e.g. if have 10^6 cells not even a 99.99% kill will clean it
what is important in biocide use
Appropriate “in use” concentration must be used
how long must biocide be left to work
Sufficient contact time (leave the antibacterial there for long enough, so get enough log drops to ensure its done its job to reduce microbes to safe level) must be used to ensure to allow the predicted population of microbes to be killed
what do biocides need
Relies on intimate contact with cell wall and membrane, needs to come into contact with cell wall if it is a biocide
what do biocides do
Physical structures are damaged and can no longer carry out vital processes e.g. respiration
what happens when biocides are used at sub-lethal concentrations
damage may be repaired/tolerated
Reversible growth inhibition occurs = sub-lethal injury
why are biocides used at sub-lethal levels constantly
When get damage that is not killing the cells but cells are having to put in energy to repair or to cope with the system they are expending energy to do this, which will inhibit growth
how do viruses repair
either dead or alive, cannot repair self if a virus
what are major groups of biocides
phenols
carboxylic acid
what do phenols do
damage to proteins affects membrane permeability & general cellular functions
what is an example of a o-phenylphenol
lysol
soaps in hospitals
what is the difference between phenol and o-phenylphenol
Phenol is toxic
O-phenylphenol is less toxic, not toxic to use
what do alcohols do to proteins
proteins denaturant
what do alcohols do to lipids
will dissolve lipids (effect membrane structure and function)
what do alcohols aid in cleaning
detergent action (help to wipe things off surfaces)
what can we use on our skin to sanitise
ethanol for skin sanitisation (not toxic for us)
rapid sanitising when moving between areas
what can’t we use on our skin to sanitise
methanol for surface sanitisation (toxic)
why is ethanol effective against viruses
denatures protein so is very good against viruses, as it cannot repair
what are the halogen biocides
iodine
chlorine
what are the biocides
alcohol halogens phenols quaternary compounds metals
what are the effects of halogens on cellular components
oxidation of cellular components
what does iodine do
will specifically combine with tyrosine residues, often found in active sites of enzymes
inhibit a wide range of different enzyme activity
what is iodine used for
used with surfactants as acidic iodophores
what does the chlorine biocide do
Chlorine and water form Hypochlorous acid and hydrochloric acid
hypochlorous acid will break down to release nascent oxygen
what does chlorine do to protein
inactivates proteins
what is chlorine used for
used in water disinfection and rinse waters
what is a quaternary compound
cationic detergents
what do cationic detergents
wetting ability
what do quaternary compounds do
denatures proteins
what are quaternary compounds good at
inactivating a wide range of microbes as affects membrane integrity affected
what are the characteristics of quaternary compounds
low toxicity
non-corrosive
what is the difference between quaternary compounds and chlorine
quaternary compounds don’t corrode metal, unlike chlorine
what is quaternary compounds used for
extensively used for equipment as not corrosive
what is the downside of using quaternary compounds
Expensive not easily made, so only use when no other alternative
what is the general structure of quaternary compounds
Nitrogen group in the middle with various R groups and is complexed with an ion
what action do metal biocides have
oligodynamic action
when are metal biocides active
very low concentrations
what do metal biocides do
combines with -SH (sulfhydryl) groups of proteins & inactivates them – so inactivates a wide range of microbes, by poisoning a lot of different processes
what is added to reservoirs to remove fungi and algae
CuSO4 copper sulphate added to reservoirs
what is an example of algicide and fungicide
copper sulphate
what is a mild fungicide
zinc
what is used for athlete
zinc
what is an example of nanotechnology silver-containing
materials being developed, plastic tubs for food containers, low levels of silver leach out of the plastic and go into the food, so has contact so it works against microbes
what is used to purify water
silver
what is a problem with killing fungi
fungi is that a lot of their biochemistry (enzymes, structure) are very similar to ours, need to find something that will not effect us
Zinc good as we don’t not absorb it very well
what is a biocide that is an oxidising agent
H2O2 hydrogen peroxide forms highly reactive superoxide (O2-)
what does hydrogen peroxide do
rapidly degrades to O2 and H2O
what does oxidising agent biocide do
Disrupts disulphide bonds
what effect does disrupting disulphide bonds
Disulphide bonds primarily in membrane and cell wall, targeting things on the outside of the cell, it wont penetrate as it is so short lived
what can be used to to clean wounds
hydrogen peroxide kills obligate anaerobes
what are some of the characteristics of biocides
Alkylating agents
Disrupts both proteins and damages DNA
Donates CH3 or similar groups to DNA
causes inactivation of protein and DNA
what can be used to sterilise equipment in plastic packaging
Ethylene oxide can diffuse through the semipermeable layer and sterile the equipment inside the plastic packaging
what dyes are there that can be used to treat skin/wound disinfectants
acridine orange
crystal violet
why can’t acridine orange be used
inhibits DNA replication and causes mutations
why can’t crystal violet be used
inhibits cell wall synthesis of Gram- positive bacteria, at high concentrations will cause mutations
what is important to consider when choosing a disinfectant
1) surface to be cleaned (alive, inert, will it be in contact with food etc)
2) concentration of organic matter present
3) importance of toxic residues
what is important to consider when making disinfectant
If have a lot of organic spoil on a surface e.g. food or meat residue the chemical will also combine with the proteins in that, which dilutes them out. When designing disinfection have to think about how much will you need as some will be absorbed by other organic material in the system
if targeting a gram negative bacteria what disinfectant is best to use
one that attacks lipids, will be most effective as have a lipid layer on outside
what biological factors will affect disinfectants
Capsules may offer some protection by preventing biocide getting to active site
how does the capsule effect the disinfectant
Slime layer / capsules protect self against environments
The first thing the chemical comes to is the slime layer, protected as it will be inactivated before it gets to the target site in the cell
how does a biofilm form
- Cells that are floating around in the liquid phase of the environment will attach to surface. Cells undergo a change of gene expression (adaptive process)
- Capsule production induced
- Biofilm starts to thicken
- Complex communities with water channels which will aid nutrient exchange
- Cells revert to planktonic phenotype & are shed from biofilm
what type of process is biofilm formation
adaptive process
what does biofilm formation require
gene expression
what may biofilm formation indicate
Often see this as a response of microbes growing in difficult environments
