IC6 Definitions + Concepts for Disinfection Flashcards
Biocides have ____ spectrum of activity than antibiotics
Broader
They may have multiple targets
Describe the difference between chemical sterilants, high-level disinfectants, and low level disinfectants
Chemical sterilants: kill spores with prolonged exposure times (3-12h)
High-level disinfectants: kill all microorganisms except spores, with shorter exposure time
Low-level disinfectants: kill most vegetative bacteria, some fungi, some viruses
What is the difference between cleaning and decontamination?
Cleaning: removal of visible soil from objects and surfaces (can be done using water w detergents or enzymatic products), remove both inorganic and organic materials that may interfere with effectiveness of disinfection
Decontamination: remove pathogenic microorganisms from objects
Describe the difference between gram negative and gram positive bacteria
Gram negative: plasma membrane, thin peptidoglycan layer, outer membrane
Gram positive: plasma membrane, thick peptidoglycan later, NO outer membrane
Bacteria envelope: polysaccharide layer that lies outside the cell envelope
Describe the virus structure
Non-enveloped virus
Enveloped virus: phospholipids and proteins with some viral glycoproteins
Capsid: oligomeric protomers between genome and envelope (protein shell that encloses genetic material)
What are the 7 factors that affect efficacy of both disinfection and sterilization?
(includes intrinsic qualities of organism + chemical and physical environment)
- prior cleaning of object
- organic and inorganic load present
- type and level of microbial contamination (number of microbes)
- conc., potency, exposure time of germicide
- physical nature of object (crevices, hinges, lumens)
- presence of biofilms (colony of microorganism tightly attached to surfaces, resistant)
- physical and chemical factors: temperature, pH, relative humidity, water hardness
Why is preliminary cleaning required?
increase margin of safety, shorten exposure time required to kill microbial load
note that direct contact is necessary for efficacy of germicide
Explain the innate resistance of the following microorganisms:
1. Spores
2. Mycobacteria
3. Gram-negative bacteria
- Spores have spore coat and cortex that act as barrier
- Mycobacteria have waxy cell wall (mycolic acid in the lipid-rich cell walls) that prevents disinfectant entry
- Gram negative bacteria have outer membrane that acts as barrier
How may temperature affect the efficacy of disinfectants? Give examples.
Increase temp => degradation (reduce stability)
Increase temp => vaporization [e.g., Ethanol, low BP]
Increase temp => QAC more effective as stable up to 60-70dc
How does water hardness reduce the rate of kill of certain disinfectants?
Hard water contains minerals such as calcium and magnesium ions (divalent cations) that can interact with the disinfectants to form insoluble precipitates/complexes => less disinfectant at site of action, reduce rate of kill
*Testing of disinfectants often involve hard water (used to standardize the test)
What are the two ways in which organic matter (e.g., serum, blood, pus, fecal) may interfere with the antimicrobial activity of disinfectants?
- Chemical reaction w germicide => reduce potency via full/partial chemical inactivation
- Protection by occlusion in salt crystals => precipitation/complexation or inclusion
Duration of exposure may affect efficacy of disinfectant. How to determine the minimum exposure time required?
Select most resistant organism, determine duration of exposure
What are biofilms?
Thick masses of cells and extracellular materials that are tightly attached to surfaces, not easily removed.
Consist of heterogenous colony of microorganisms that have varying susceptibility to disinfectants
Microbes within them are resistant to disinfectants by multiple mechanisms.
Biofilms are more resistant to drying, UV radiation, and antimicrobial agents compared to free microorganisms.
What are the 4 mechanisms of biofilm resistance?
- Layers of older biofilms shield microorganisms inside
- Genotypic variations of the bacteria (spontaneous mutations)
*may have antibiotic resistance genes
*the surviving bacteria containing the resistant genes can replicate and also pass on resistant genes to other bacteria within the biofilm colonies - Microbial production of neutralizing enzymes produced by biofilm against disinfectant
- Physiologic conditions (environmental conditions in the colony that inactivate the disinfectant) - note this is less effective and more difficult to achieve as a change in pH is easier to achieve in microenvironment than water pipe
Adhesiveness to surface: necessary for growth, but less important for survival (can have detached biofilms)
What might trigger biofilm resistance (genotypic variations) mechanism?
Ans: Exposure to sub-MIC concentrations of disinfectants
(*this could result from incorrect use of disinfectant or may also be due to thick layer of older biofilms that prevent disinfectant from reaching the inner layers of microbes in the biofilm thus leading to sub-MIC concentrations)
- causes selection pressure and development of resistance
- trigger stress responses in bacteria, and induce temporary, adaptive changes in the composition and permeability of their cell envelopes or in the activity of their efflux pumps
bacteria in biofilm can have efflux pumps
or can have less permeable cell envelopes
What are biofilms usually treated with?
Chlorine
- effective for detaching biofilms from surfaces
- no toxic residues
- unaffected by water hardness
- release toxic chlorine gas, corrosive to metals
Ozone
UV radiation
*Key property: fast acting, eliminated rapidly, do not leave residue
Chloramine is the conventional treatment for maintenace
- effective for a longer time as it releases chlorine slowly (compared to chlorine/hypochlorite)
- but may prefer chlorine if require higher concentration treatment
What is starvation treatment for biofilms?
Enrichment of water with 0.9% sodium chloride
- removes water from nutrients required for microorganism growth
- cell death by osmosis
=> higher detaching rate of bacteria in biofilms
Were stubborn or detached biofilms found to have more antibiotic resistant genes?
Detached
How do lack of nutrients, or nutrient accessibility affect efficacy of the disinfectant against biofilms/aid in biofilm resistance?
Lack of nutrients: cells die, dead cells can act as physical barrier against disinfectant
Nutrient access: cells can organize themselves as biofilms and become more resistant
Can microorganisms grow in distilled water?
No, distilled water has low conc. of ions
Death by osmosis
Explain antibiotics/disinfectant cross resistance
Resistance arise when bacteria acquire drug resistance genes or mutations in genes that alter their sensitivity to an antibiotic
Mechanisms such as efflux pump may work for both disinfectants and antibiotics
However, mechanisms such as modification of a protein target work for antibiotics only because disinfectants have broader activity and are not affected by small structural modifications (e.g., induce denaturation of proteins)
What are some examples whereby contamination of disinfectant occur due to mistake during handling and storage?
- Use of over diluted solutions
=> disinfectant not at MBC, can end up being contaminated - Use of tap water to dilute germicide
- Refilling of small-volume dispensers from large volume stock containers
- Improper selection of inappropriate product (e.g., use low level disinfectant rather than high level disinfectant to disinfect endoscope)
