IC6 Flashcards
Activity of disinfectants
Eliminates many or all pathogenic microorganisms, except bacterial spores, on inanimate objects
Classification of disinfectants
- Chemical sterilants: kill spores with prolonged exposure times (3–12 hours)
- High-level disinfectants: kill all microorganisms except large numbers of bacterial spores at shorter exposure periods
- Low level disinfectants: kill most vegetative bacteria, some fungi, and some viruses in a practical period of time
Factors affecting the efficacy of disinfection
- prior cleaning of the object;
- organic and inorganic load present;
- type and level of microbial contamination;
- concentration of and exposure time to the germicide;
- physical nature of the object (e.g., crevices, hinges, and lumens);
- presence of biofilms;
- temperature and pH of the disinfection process
Antiseptics Vs Disinfectants
- Antiseptics are germicides applied to living tissue and skin;
- Disinfectants are antimicrobials applied only to inanimate objects;
- Antiseptics are used only on the skin and not for surface disinfection;
- Disinfectants are not used for skin antisepsis because they can injure skin and other tissues.
Term for both antiseptics and disinfectants
Biocides
Example of fungi
Yeasts / molds
What are prions?
misfolded proteins that may transmit their misfolded shape onto normal variants
Why are spores resistant to disinfectants?
spore coat and cortex act as a barrier
How does mycobacteria acquire resistance to disinfectants?
contains waxy cell wall that prevents disinfectant entry
How does gram negative bacteria acquire resistance to disinfectants?
they possess an outer membrane that acts as a barrier to the uptake of disinfectants
Does halving the concentration of the disinfectant mean double the time to achieve disinfection?
Not necessarily; not a linear relationship
Most important factor influencing the activity of gaseous disinfectant
Relative humidity
Examples of gaseous disinfectant
ethanol, chlorine dioxide, and formaldehyde
How does water hardness affect the rate of kill of certain disinfectants?
Reduces the rate of kill: divalent cations in the hard water interact with the disinfectant to form insoluble precipitates
Two ways in which organic matter (like serum, blood, pus or fecal ) can interfere with the antimicrobial activity of disinfectants
1) Chemical reaction between the germicide -> Reduction in potency or full chemical inactivation
2) Protection by occlusion in salt crystals -> Precipitation or inclusion
Mechanisms that make microbes within biofilms resistant to disinfectants
• layers of older biofilms,
• genotypic variation,
• neutralizing enzymes,
• physiologic conditions
Is isopropanol against non-enveloped viruses?
No. It is active against enveloped viruses.
MOA for Ammonia (aq)
Saponify lipids within envelopes of microorganisms
Is alcohol bacteriostatic/ bactericidal?
Bacteriostatic
Concerns for ammonia use
- Irritant for eyes and gastric system
- May release chloramine (toxic) when mixed with bleach
What could be added to enhance alcohol MOA (denaturation of ptns)?
Water
MOA for aldehyde
Alkylation of sulfhydryl, hydroxyl, carboxyl and amino groups of microorganisms -> alters RNA, DNA & protein synthesis
Concern for aldehyde
Toxic and odour
Ppty of Ortho-phthalaldehyde (OPA) that assists its entry to outer layers of mycobacterium & gram-negative bacteria
Lipophilicity
Advantages and limitations of OPA
(+) Excellent stability over wide range of pH 3-9
(+) Not irritant to eyes and nasal passages
(+) Odourless
(+) Excellent material compatibility
(-) Stains protein grey (incl unprotected skin) -> handle with caution
Is Chlorhexidine bacteriostatic/ bactericidal?
bactericidal
Name 2 biguanides
Chlorhexidine and alexidine
Activity of chlorhexidine is ___ dependent and greatly ____ in the presence of _____.
pH; reduced; organic matter
Advantages of alexidine over chlorhexidine
Faster onset of bactericidal activity & significantly faster alteration in bactericidal permeability compared to chlorhexidine
MOA for hypochlorite
Oxidation of sulfhydryl enzymes;
Ring chlorination of amino acids;
Inhibition of chlorine synthesis;
DNA disruption;
Loss of intracellular contents
Advantages and limitations of hypochlorite
(+) Do not leave toxic residues
(+) Unaffected by water hardness
(+) Inexpensive
(+) Fast acting
(+) Removes dried/ fixed organisms and biofilms from surfaces
(+) Low incidence of serious toxicity
(-) Ocular irritation
(-) Burns mouth, throat & stomach
(-) Corrosive to metals in high conc
(-) Inactivation by organic matter
(-) Release of toxic chlorine gas
Most widely used chlorine disinfectant
Hypochlorite
Activity of hypochlorite largely attributed to ______
undissociated hypochlorous acid (HOCl)
Efficacy of hypochlorite decreases with _______
increasing pH (more hypochlorite ion, OCl-)
How is Sodium dichloroisocyanurate best prepared? (dosage form)
From tablet; stable and long release
What contributes to the prolonged effect of Sodium dichloroisocyanurate?
Only 50% of available chlorine is free (HOCl and OCl-) and remainder is combined (mono & dichloroisocyanurate) -> remainder released when the free ones are used up
Example of iodophor
Povidone-iodine
MOA for iodophor
‘Free’ iodine (I2) penetrate cell wall of microorganism quickly -> disruption of protein & nucleic acid structure and synthesis
Dilution of iodophor ____ iodine linkage to _____ which ____ free iodine and ____ action.
Weakens; carrier polymer; increases; faster
MOA for Hydrogen peroxide
(H2O2)
Acts as an oxidant; produces free radical (*OH) which attack essential cell components incl lipids, proteins and DNA
Does H2O2 act against spores?
Yes; longer contact time to kill spores
Presence of _____ in H2O2 render low conc less effective
catalase/ peroxidase
Concerns for H2O2
(-) Short half life (due to decomposition in H2O and H2O2)
(-) Irritant for eyes
MOA for Peracetic acid
Denatures proteins and enzymes & increases cell wall permeability by disrupting sulfhydryl (-SH) and sulphur (S-S) bonds
advantages of peracetic acid
(+) Decomposes to safe by-products (acetic acid and oxygen)
(+) Free from decomposition by peroxidase
(+) Remains active in presence of organic loads
Peracetic acid is a more potent biocide than _____ at low conc
H2O2
MOA of phenols
Induces progressive leakage of intracellular constituents incl release of K+ (1st index of membrane damage)
Example of phenol
Chloroxylenol
Advantages & limitation of phenol
(+) Non-toxic, non-irritant as an excipient in topical products;
(-) toxic upon oral use/ eye contact
Example of Silver compounds
Silver sulfadiazine (most common) & Silver nitrate
Which silver compound has a broader spectrum?
Silver sulfadiazine
Why is Mercuric chloride (HgCl2) no longer used?
(-) Highly toxic and corrosive
(-) Accumulates in kidney -> corrosive damage -> kidney failure
Example of QAC
Benzalkonium chloride
What is Benzalkonium chloride usually used as?
antimicrobial preservative
Activity of benzalkonium chloride
More active against gram positive; minimal activity against endospores & acid-fast bacteria
Vapour phase sterilants
Ethylene oxide and formaldehyde
What could vapour phase sterilants be used on?
heat-sensitive medical devices and surgical supplies
Uses for UV lamps as disinfectant
Mostly used to supplement current hospital or laboratories cleaning and disinfection of contaminated surfaces.
Recently used for water treatment (usually coupled with ion sequestration and chlorine disinfection).
