RA1: Sterilization, Disinfection and Antisepsis

Question 1

Need for sterilization, disinfection and antisepsis?

Answer 1

• Limit spread of infectious agents. 1/3rd of hospital-acquired infections are preventable. Most HAIs were caused by G+ bacteria prior to antimicrobial therapy. After discovery of antibiotics, G- took over. Even higher need now given antibiotic resistant G+ and multi-drug resistant G- bacteria.

Question 2

Define sterilization, disinfection and antisepsis

Answer 2

• Sterilization: total destruction or physical removal of all microorganisms including resistant forms such as bacterial spores, mycobacteria, nonenveloped viruses and fungi
• Disinfection: removing or killing most, but not all viable organisms, not including mycobacteria, viruses, fungi and bacterial spores which may survive this process
• Antisepsis: agents that lower number of microorganisms on skin surfaces, none of these agents kill bacterial spores, but are efficacious against vegetative bacteria and are very safe

Question 3

Methods of sterilization and mechanism of action

Answer 3

1. ) Moist heat: saturated steam under pressure (121-132 for 15+ minutes) – irreversibly denatures proteins, causes ss DNA breaks and compromises membrane integrity – kills spores
2. ) Dry heat: oven (1 h at 170 C, 2 at 160, 3 at 150) – irreversibly denatures proteins, causes ss DNA breaks and compromises membrane integrity – kills spores, but may not eliminate pyrogens
3. ) Ethylene oxide gas: colorless gas toxic – kills by alkylating protein, DNA and RNA within cells preventing normal metabolism and replication
4. ) Irradiation: UV radiation – kills by eliciting DNA damage through production of free radical, blocks microbial replication

Question 4

How to destroy prions?

Answer 4

• Boiling in 1N NaOH for 10 minutes followed by extended autoclaving

Question 5

3 categories of disinfection - examples

Answer 5

1. ) High-level disinfection: approaches sterilization in effectiveness in that it destroys all microorganisms, except large numbers of bacterial spores (may kill some) – used on medical equipment that cannot be sterilized such as endoscopes that come into contact with blood and tissues
   - examples: glutaraldehyde, oxidizing agents such as peracetic acid, h2o2, chlorine compounds such as bleach
2. ) Intermediate-level disinfection: kills mycobacteria, bacteria, most viruses, most fungi, but not bacterial spores
   - examples: alcohols, iodine containing compounds, phenolic compounds
3. ) Low-level disinfection: kills most vegetative bacteria, some fungi and some viruses in a reasonable period of time
   - examples: quaternary ammonium compounds to clean non-critical instruments that come into contact with pt but don’t penetrate mucosal layer

Question 6

Qualities to take into account when choosing disinfectant

Answer 6

• Antimicrobial activity, solubility, stability, penetration, non-toxicity to humans, corrosivity, non-staining etc.

Question 7

Antisepsis compounds and MOA

Answer 7

1. ) Alcohols: kills mycobacteria, NOT SPORES. Denature bacterial proteins, inhibit synthesis of metabolites essential for cell division – more effective in presence of water (70% more effective than 95%), less effective than iodine
2. ) Phenolic compounds: penetrate and disrupt cell wall in high concentration and denature proteins and lipids in cell membrane, lyse cells, also inactivate essential enzymes, NO KILLING OF SPORES
3. ) Iodine solutions: most effective skin antiseptics and should be applied before obtaining blood culture and installing IV catheters to remove staph epidermidis – two types:1.) tincture of iodine (irritates skin) and 2.) iodophors (non-skin irritant) – NO KILLING OF SPORES, more toxic than alcohol
4. ) Chlorhexidine: broad antimicrobial activity, but slower than alcohols – kills by membrane disruption – NO KILLING OF SPORES.
5. ) Quaternary ammonium compounds: attack energy-producing enzymes, denature cell proteins and disrupt cell membranes – not effective against pseudomonas, viruses, spores, mycobacteria
6. ) Triclosan: this is an antiseptic in hand soaps, some tooth pastes. NO KILLING OF SPORES. Inhibits bacterial lipid synthesis and may also disrupt cell membrane at high concentrations.

Question 8

Is boiling a method of sterilization?

Answer 8

• No, it is a method of disinfection