1. When studying the activities of agents used for control of microbial growth, concentrate on understanding the listed objectives and the material shown in bold.
This PowerPoint is a summary of main points and the World file is a slightly fuller explanation that can be used as a resource to fill in gaps. It is not comprehensive

2. Part I Objectives - Clinical Settings medicasettings```````
Describe the physical processes being used to control microbial growth and compare the efficiency of both wet vs dry heating and u.v. vs -irradiation for sterilization.
Explain why filtration of air or liquids does not remove virus particles
Define “antiseptic” and “disinfectant.”
Describe the mode of action of phenol, alcohols, halogens, surfactants, alkylating agents (e.g. aldehydes such as glutaraldehyde) and heavy metals when used for antisepsis or as disinfectants

3. Microbial control in medical settings medicasettings```````
Prevention of infection is a major concern in medical procedures, especially those associated with direct access to blood.
Controls:
Physical
Chemical

4. Physical Controls - Heat medicasettings```````
Wet heat is more effective than Dry heat.
Boiling alone does not kill several spore-forming bacteria (Clostridium and Bacillus), but generally kills bacteria that do not form spores

5. Heat Sterilization: Wet heat: 121º C, 15 min
irreversible inactivation of spores.
Membrane disruption and protein denaturation:
Dry heat: 160º C, 120 min
Oxidation of constituents and protein denaturation

6. Sterilization without heat:
Filtration: Does not remove viruses
0.22 um um diam of pores remove bacteria and fungi. (May allow mycoplasma to squeeze through).
Ionizing radiation: Penetrates well.
Forms hydroxyl free radicals and peroxides.
Widely used for plastics
UV light: Does not penetrate well, used for surfaces.
Forms pyrimidine dimers in DNA.

7. Chemical Control - Summary
Phenol and phenolics: Plasma membrane
Protein denaturation
Alcohols: Lipid solvents
Surfactants:
Quaternary Plasma membrane via cationic phospholipids
Soaps, home Plasma membrane via detergents lipoproteins

8. Chemical Control - Summary (cont.)
Halogens:
Iodine tyrosine oxidation
Cl as HOCl oxidizer
Alkylating agents: denature proteins via attachment of methyl and ethyl groups
Heavy metals: protein denaturants

9. Chemical Control: Disinfectants: inanimate objects
Antiseptics: used on body surfaces

10. (i.e., can be hard to inactivate microbes
Chemical Control:
Halogens:
Strong oxidizing agents reactive with several types of molecules. (e.g; iodine binds to tyrosine).
Chlorine used as HOCl (bleach). Effective at ppm, but activity reduced rapidly in presence of organic matter.
(i.e., can be hard to inactivate microbes
in blood ****)

11. Chemical Control: Halogens: Iodine in antisepsis Tincture of iodine
2% iodine in NaI + dilute alcohol
Betadine
iodine in a detergent

12. Chemical Control: Phenol and phenolics:
Disrupt plasma membranes and denature proteins.
Lead to leakage of cellular components
1865: Joseph Lister used 5% phenol to disinfect surgical instruments and dressings. Revolutionized surgery

13. Chemical Control: Phenol and phenolics: 5% phenol
Cresol (methyl phenol) in coal tar soaps
Hexachlorophene in soaps
(chlorinated biphenyl with excellent activity against Gram-positive bacteria)
? Can cause neurologic side-effects

14. Chemical Control: Alcohols: (e.g.; isopropyl alcohol)
Lipid solvents and some protein denaturation activity
Widely used as 70% ethanol or isopropanol for disinfection of thermometers etc.

15. Chemical Control: Surfactants: (soaps and detergents)
Surface active substances contain both hydrophilic and hydrophobic groups. Activity causes decreased surface tension of water.
Quaternary ammonium compounds
Maintain charge N+ and Cl- with hydrophobic chain.
Allows reaction with phosphate in phospholipids

16. Chemical Control: Surfactants: (soaps and detergents)
Cationic detergents: Hospital floors and walls, food processing plants, restaurants
Anionic detergents: Act on lipoprotein portion of membrane. Milder than cationic detergents. (Home use in soap and detergent)

17. Chemical Control: Alkylating agents: Formaldehyde
Embalming, histology, vaccines (kills but antigenic epitopes may survive)
Glutaraldehyde
Certain delicate surgical instruments

18. Chemical Control: Heavy metals: Hg, Ag, Cu
Bind to -SH groups and cause protein denaturation.
Organic mercury compounds for antisepsis on skin and urethral irrigation, + disinfection of instruments. (merthiolate)
1% silver nitrate for prevention of ophthalmia neonatorum (Neisseria gonorrhoeae)