IC6 - Disinfectants Flashcards
Sterilisation
Process that eliminates ALL forms of microbial life carried out in health-care facilities by physical or chemical methods
Disinfection
Process that eliminates MANY or ALL pathogenic microorganisms EXCEPT for bacterial spores, on INANIMATE objects
Factors affecting the efficacy of disinfectants
- Prior cleaning of object*
- Organic and Inorganic load present
- Type and level of microbial contamination
- Concentration and exposure time to the germicide*
- Physical nature of the object (total surface area)
- Presence of biofilms*
- Temperature and pH of disinfection
Chemical Sterilants
Disinfectants that kill spores upon prolonged exposure (3-12 hours)
High-level Disinfectant
Kill all microorganisms except bacterial spores with the usual concentration and short exposure time period eg. Aldehydes
Cleaning
Removing visible soil
Biocides
Broader spectrum of activity than antibiotics and have multiple targets. COmprises of disinfectants and antiseptics
Examples of innate resistance of microorganisms
- Spores - spore coat and cortex act as barrier
- Mycobacteria - waxy cell wall that prevents disinfectant entry
- Gram-negative bacteria - outer membrane that acts as a barrier to the uptake of disinfectants
How does temperature affect disinfectant efficacy?
Most stable disinfectant increase in efficacy at higher temperatures.
However, some may suffer degradation (eg. ethanol evaporating in hot environment)
How does pH affect disinfectant efficacy?
pH can either affect cell or disinfectant. Recommended pH> 4-5
Increase in pH improves antimicrobial activity of some disinfectants (eg. aldehydes and QAC).
However, it may decrease antimicrobial activity (eg. phenols, hypochlorites and iodine).
How does relative humidity affect disinfectant efficacy?
Gaseous disinfectants, water added improve antimicrobial activity (eg. ethanol, formaldehyde, CO2)
How does water hardness affect disinfectant efficacy?
Decrease kill of some disinfectants because divalent cations in hard water interact with disinfectants to form insoluble precipitates, leading to less disinfectant available at site of action
How does organic/inorganic matter affect disinfectant efficacy?
- Chemical reaction with disinfectant, reducing potency or inactivating it.
- Protection by occlusion in salt crystals via precipitation (less common) or inclusion (more common)
Biofilms
Resistant to disinfectants via multiple mechanisms
1. Layers of older biofilms (survive after selection pressure has been applied)
2. Genotype variation* (Environment favors this)
3. Neutralizing enzymes
4. Physiologic conditions
MOA of Alcohols
Denatures proteins (activity increases with H20), bacteriostatic by inhibiting production of metabolites essential for rapid cell division
Isopropyl VS Ethanol
Isopropyl more lipophilic and viscous, more efficacious against bacteria and non-enveloped viruses, Ethanol more efficacious for enveloped virus
MOA of Ammonia
Saponifying lipids (complex lipids into salt) within the envelopes of microorganisms
Ammonia disinfectants
Irritant to eyes and gastric system (pH: 11-12)
Eg. mixed with bleach to give toxic chloramine.
MOA of Aldehyde
Alkylation of SH, OH, CO, NH2 groups of microorganisms, alters RNA, DNA and protein synthesis.
Aldehyde disinfectants
High-level disinfectant, large spectrum of activity.
Liquid or Gaseous (more common).
Toxic and much odour, not used for antiseptic.
Eg. Paraformaldehyde, Ortho-phthaldehyde (OPA)
Ortho-phthaldehyde (OPA)
Action: Cross-linking agent, may block the germination process, and lipophilic to assist uptake through mycobacteria and gram-negative bacteria.
Stable at a wide pH range, less irritant to eyes and nasal passage, odourless
Chlorhexidine (Biguanides)
Broad spectrum bactericidal agent. pH and organic matter affect activity.
MOA of Chlorhexidine (Biguanides)
- Damage membrane
- Cross cell outer membrane by passive diffusion
- attacks bacterial cytoplasmic or inner membrane or the yeast plasma membrane
Alexidine VS Chlorhexidine (Biguanides)
Alexidine faster onset of bactericidal activity, faster alteration in bactericidal permeability, produce lipid phase separation to destroy bacterial membrane.
MOA of Chlorine and Chlorine compounds
- Oxidation of SH enzymes and AA
- Ring chlorination of AA
- Inhibition of protein synthesis
- DNA disruption
- Loss of intracellular contents
Adv of Chlorine and Chlorine Compounds (Hypochlorites)
- Broad spectrum activity
- No toxic residues
- Unaffected by water hardness
- Used against biofilm
- Cheap
Disadv of Chlorine and Chlorine Compounds (Hypochlorites)
- Occular Irritation
- Burns (mouth, throat, stomach)
- Corrosiveness to metals in high concentrations
- Inactivated by organic matter
- Release if toxic chlorine gas
- Decreased efficacy when increase in pH (dissociation of more active HOCl-)
Alternative Chlorine Compounds
Chloramine, Sodium dichloroisocyanurate (solid tablets) - keep concentrations high for longer time, prolonged bactericidal effect
MOA of Iodine and Iodophors
penetrate cell wall quickly and disrupt protein and nucleic acid structure and synthesis
Iodophor
Combination of iodine and solubilizing agent, the complex provides a sustained-release reservoir of iodine and releases a small amount of free iodine. EG. polyvinylpyrrolidone with iodine. Dilution of povidone-iodine weakens iodine linkage to carrier, more free iodine, better activity
Adv of Iodine and Iodophors
Can be used as antiseptic and disinfectant
MOA of Peroxygens (H2O2)
H2O2 acts as an oxidant by producing OH free radicals that attack essential cell components (lipids, proteins and DNA), destroying membrane.
Adv of Peroxygens
- Stable liquid *may contain stabilisers to prevent decomposition)
- (High-level disinfectant) broad-spectrum efficacy against all viruses, bacteria, yeasts, and bacterial spores
Disadv of Peroxygens
- More gram-pos cover, less-gram neg cover
- Catalase and peroxidase in microorganisms decrease activity of peroxygens
Accelerated hydrogen peroxide
More efficacious than H2O2
1. has surfactant to disrupt bacterial cell outer layer
2. has chelating agent to reduce water hardness and metal content
3. has emulsifier to improve stability and prolong activity
Peracetic acid
More potent than H2O2 (Sterilant)
MOA: denatures proteins and enzymes and increase cell wall permeability by disrupting SH and S-S bonds
Safer and not subject to decomposition
Low temperature liqid sterilant
MOA of Phenols
Induces progressive leakage of intracellular constituents, release of K+, causing membrane damage.
Uses of Phenols
Antifungal and Antiviral properties
Antiseptic, disinfectant and preservative
Chloroxylenol
MOA: disrupt microbial cell walls, inactivate cellular enzymes
Nontoxic and nonirritant but not to be consumed or used in eye contact.
Used with chelating agent to reduce activation by calcium ions
Diamidines
Bacteriostatic agents used in wound treatment
MOA: Inhibits oxygen uptake and leakage of AA, killing microorganism
Silver compounds
Antifungal properties
Silver ions interact with thiol (SH) groups in enzymes and proteins, plasma, cytoplasmic membrane and nucleic acids
Silver sulfadiazine: broader spectrum inducing membrane blebs in susceptible bacteria
MOA of QAC
- adsorption and penetrate cell wall
- React with cytoplasmic membrane and cause membrane disorganization
- Leakage of intracellular low molecular weight material
- Degradation of proteins and nucleic acids
- Wall lysis caused by autolytic enzymes
Uses of QAC
Cationic detergents, broad spectrum.
Bactericidal, fungicidal, virucidal against enveloped viruses.
Disinfection of UNBROKEN skin
Benzalkonium Chloride
QAC used as preservative
More gram-pos than gram neg coverage.
Minimal activity against bacterial endospores and acid-fast bacteria
Activity dependent on alkyl composition of mixture
Vapor Phase Sterilants
glutaraldehyde, peracetic acid and H2O2
Ethylene oxide and formaldehyde (broad spectrum alkylating agents), reactive with SH and enzyme-reactive groups
