1. Chapter 7 The Control of Microbial Growth TERMINOLOGY Sepsis refers to microbial contamination. Asepsis is the absence of significant contamination. Sterilization: Removal of all microbial life Commercial Sterilization:

2. Disinfection: Killing of vegetative microbes on nonliving objects Antisepsis: Killing of vegetative microbes in/on living tissue Degerming: Removal of microbes from a limited area Biocide/Germicide: Kills microbes Bacteriostasis: Inhibits, does not kill microbes

3. Factors influencing death rate are: Number of microbes Environmental influences (ie. Organic substances, biofilms, temperature, pH) Biofilms: Biofilms Time of exposure Microbial characteristics [antimicrobial agent] Microbe Death by Antimicrobial Agents

4. Alteration of membrane permeability Lipids and proteins are altered Intracellular substances leak out of cell Damage to proteins Denaturation of enzymes, etc. Loose their structure and function Damage to nucleic acids Damaged DNA and RNA prevents production of vital proteins Actions of Microbial Control Agents

5. Heat denatures proteins Boiling water (May not kill spores) Autoclave: generates very high pressure and temperature via steam Steam must contact surface to kill microbes Moist Heat Figure 7.2

6. Pasteurization reduces spoilage organisms and pathogens via heating Thermoduric (i.e. thermophiles) organisms survive Pasteurization treatments High-temperature short-time (HTST): 72°C for 15s Ultra-high-temperature (UHT): 140°C for 3s Pasteurization

7. Dry Heat Sterilization: Direct flaming Incineration Hot-air sterilization Dry Heat Hot-airAutoclave Equivalent treatments170˚C, 2 hr121˚C, 15 min

8. Filtration removes microbes Low temperature inhibits microbial growth: Refrigeration Deep freezing Desiccation prevents metabolism Hypertonicity causes plasmolysis Other Physical Methods of Microbial Control

9. Radiation damages DNA and other organic molecules Ionizing radiation (X rays, gamma rays, electron beams) Nonionizing radiation (UV) Microwaves kill by heat; not especially antimicrobial Other Physical Methods of Microbial Control

10. Evaluating a disinfectant Use-dilution test 1. Stainless steel cylinders are inoculated with Staphylococcus aureus, Salmonella choleraesuis, Pseudomonas aeruginosa 2. Cylinders are dried in an incubator 3. Cylinders are placed in test disinfectant 4. Cylinders are incubated in broth media Chemical Methods of Microbial Control

11. Disk-diffusion method

12. Types of Disinfectants/Antiseptics Figure 7.7 Phenol Phenolics: Modified phenol reduced irritation, enhanced antibacterial action ie. Lysol Bisphenols: Hexachlorophene Triclosan (2 nd link)Triclosan2 nd link Found in many household items

13. Chlorhexidine surgical hand scrub preoperative patient scrub Halogens: Iodine: skin disinfectant; water treatment Chlorine (ie. Bleach): water, sewage treatment; swimming pools; restaurants, etc. Types of Disinfectants/Antiseptics

14. Table 7.6 Alcohols: Ethanol, isopropanol May not be appropriate for wound cleaning May “seal in” microbes Alcohol-based handrubs Alcohol-based handrubs

15. Heavy Metals: ie. Ag, Cu Silver compounds: impregnated dressings; burn creams; catheters Copper sulfate: kills green algae in reservoirs, pools, ponds Types of Disinfectants/Antiseptics

16. Chemical Food Preservatives Organic Acids - Inhibit metabolism Sorbic acid, benzoic acid, calcium propionate Control molds and bacteria in foods and cosmetics Nitrite prevents endospore germination in meats Antibiotics. Nisin and natamycin prevent spoilage of cheese Types of Disinfectants

17. Aldehydes: Glutaraldehyde: sterilizes* hospital instrument disinfection used for embalming Types of Disinfectants

18. Gaseous Sterilants Ethylene oxide: Peroxygens Ozone = O 3 : ie. water treament Hydrogen peroxide = H 2 O 2 : ie. Food packaging; NOT good for open wounds Types of Disinfectants

19. Surface-Active Agents or Surfactants Types of Disinfectants/Antiseptics SoapDegerming Cationic detergents: Quaternary ammonium compounds = “Quats” ie. Pseudomonads can grow in Quat solutions; can Norovirus?

20. Relative Resistances to Antimicrobials Figure 7.11