1. The Terminology of Microbial Control
Sterilization-removing ALL microbial life; heat
Sterilant- a sterilizing agent
Commercial sterilization- killing C. botulinum endospores in food; used so food is not destroyed
Disinfection- removing pathogens not including endospore
Antisepsis- removing pathogens from living tissue
Degerming- mechanical removal of microbes from a limited area; using an alcohol swab
Sanitization- lowering microbial counts on eating utensils to a public health safety number

2. The Terminology of Microbial Control
Biocide/germicide- killing microbes
Fungicide- kills fungi
Virucide- inactivates viruses
Bacteriostasis- inhibiting, not killing, microbes
Sepsis- microbial contamination
Asepsis-the absence of significant microbial contamination
Aseptic surgery techniques prevent microbial contamination of wounds

3. Rate of Microbial Death
Microbes die at a constant rate.
Each minute of treatment kills 90% of REMAINING microbes.

4. Effectiveness of Treatment
Depends on:
Number of microbes
Environment (organic matter, temperature, biofilms)
Time of exposure
Microbial characteristics

5. Actions of Microbial Control Agents
Alteration of membrane permeability- damages lipids or proteins.
Damage to proteins- enzyme damage due denaturation
Damage to nucleic acids- cell can no longer replicate or carry on normal metabolic functions

6. Question:
Would a chemical microbial control agent that affects plasma membranes affect humans? 7-3

7. Physical methods of microbial control

8. Heat
Thermal death point (TDP): lowest temperature at which all cells in a culture are killed in 10 min
Thermal death time (TDT): time during which ALL cells in a culture are killed
Decimal Reduction Time (DRT): Minutes to kill 90% of a population at a given temperature

9. Figure 7.10 A comparison of the effectiveness of various antiseptics.

10. Moist Heat Sterilization
Moist heat denatures proteins by breaking H bonds
Types:
Boiling- can kill most bacterial pathogens and viruses in 10 minutes; endospores up to 20 hours
Autoclave: steam under pressure; 15psi, 121C, 15 minutes; can kill endospores
Used for media, instruments, dressings, IV equipment, syringes, ets.
Time and temperature can change due to size
Steam must contact item’s surface

11. Figure 7.2 An autoclave.
Exhaust valve
(removes steam
after sterilization)
Operating valve
(controls steam from
jacket to chamber)
Steam to
chamber
Safety
valve
Pressure gauge
Steam
Door
Steam
chamber
Air
Perforated shelf
Sediment
screen
Steam jacket
Thermometer
Automatic ejector valve
(thermostatically controlled;
closes on contact with
pure steam when air is
exhausted)
Pressure regulator
for steam supply
To waste line
Steam supply

12. Figure 7.3 Examples of sterilization indicators.

13. Pasteurization
Reduces spoilage organisms and pathogens in some food and liquids without damaging taste of product
Equivalent treatments
63°C for 30 min
High-temperature short-time: 72°C for 15 sec
Ultra-high-temperature: 140°C for <1 sec
Thermoduric(heat resistant) organisms survive

14. Dry Heat Sterilization
Kills by oxidation
Dry heat
Flaming
Incineration
Hot-air sterilization
Hot-Air
Autoclave
Equivalent Treatments
170˚C, 2 hr
121˚C, 15 min

15. Filtration HEPA- removes microbes >0.3 µm
Membrane filtration- removes microbes >0.22 µm

16. Physical Methods of Microbial Control
Low temperature inhibits microbial growth (bacteriostatic)
Refrigeration
Deep-freezing
Lyophilization
High pressure denatures proteins
Desiccation prevents metabolism
Osmotic pressure causes plasmolysis

17. Radiation Ionizing radiation (X rays, gamma rays, electron beams)
Damages DNA
Can go through barriers
Used by the food industry on meats, vegetables, and spices
Also used on dental and medical supplies
Nonionizing radiation (UV)
Has to be in direct contact
Microwaves kill by heat; not especially antimicrobial

18. Principles of Effective Disinfection
Concentration of disinfectant
Time
Substance the disinfectant is being used against:
Organic matter pH

19. Evaluating a Disinfectant
Use-Dilution Test
Disk Diffusion Method
Metal rings dipped in test bacteria are dried
Dried cultures are placed in disinfectant for 10 min at 20°C
Rings are transferred to culture media to determine whether bacteria survived treatment
Filter paper is soaked with a chemical
Placed on an agar plate with an organism on it
Look for zones of inhibition

20. Staphylococcus aureus Pseudomonas aeruginosa
Figure 7.6 Evaluation of disinfectants by the disk-diffusion method.
Zone of inhibition
Chlorine
Chlorine
Chlorine
O-phenylphenol
O-phenylphenol
Hexachlorophene
O-phenylphenol
Hexachlorophene
Hexachlorophene
Quat
Quat
Quat
Staphylococcus aureus
(gram-positive)
Escherichia coli
(gram-negative)
Pseudomonas aeruginosa
(gram-negative)

21. If you wanted to disinfect a surface contaminated by vomit and a surface contaminated by a sneeze, why would your choice of disinfectant make a difference? 7-7

22. Phenol and Phenolics
Disrupt plasma membranes
Lysol
Bacteria

23. Bisphenols Hexachlorophene Triclosan Disrupt plasma membranes
Used in hospital soaps
Staphyloccocci and Streptococci
Triclosan
Found in soaps, toothpaste, cutting boards, plastic kitchenware
Bacteria and yeast

24. Biguanides Chlorhexidine Disrupts plasma membranes
Surgical hand scrubs and preoperative scrubs
Bacteria

25. Halogens Iodine Chlorine Alters protein synthesis and cell membranes
Bacteria, endospores, fungi, viruses
Chlorine
Prevents enzyme system from functioning
Bleach
Disinfects drinking water, swimming pools, and sewage
Bacteria and viruses

26. Alcohols Ethanol, isopropanol Denature proteins, dissolve lipids
Require water
Bacteria and fungi

27. Heavy Metals Silver, Mercury, and Copper Denatures proteins
Silver nitrate- may be used to prevent gonorrheal ophthalmia neonatorum
Silver sulfadiazine- used as a topical cream on burns
Copper sulfate- is an algicide

28. Surface-Active Agents, or Surfactants
Soap- mechanical removal of microbes
Degerming
Acid-anionic detergents- dairy utensils and equipment; bacteria
Sanitizing
Quaternary ammonium compounds (cationic detergents)- fungicidal, amebicidal, virucidal
Bactericidal, denature proteins, disrupt plasma membrane

29. Chemical Food Preservatives
Organic acids
Inhibit metabolism
Sorbic acid, benzoic acid, and calcium propionate
Control molds and bacteria in foods and cosmetics
Nitrite
Prevents endospore germination
Put in ham, bacon, hot dogs, sausage
Antibiotics
Nisin and natamycin prevent spoilage of cheese

30. Aldehydes Inactivate proteins by cross-linking
Bactericidal, tuberculocidal, virucidal, sporicidal
Used on hospital instruments, endoscopes, and respiratory therapy equipment
Glutaraldehyde, formaldehyde

31. Gaseous Sterilants Denature proteins Sporicidal
Use: heat-sensitive material
Ethylene oxide

32. Plasma Free radicals destroy microbes
Used for tubular instruments used for arthroscopic and laparoscopic surgeries

33. Supercritical Fluids CO2 with gaseous and liquid properties
Use: medical implants(bones, tendons, ligaments)

34. Peroxygens
Hydrogen Peroxide
Use: contaminated surfaces

35. Figure 7.11 Decreasing order of resistance of microorganisms to chemical biocides.

36. Table 7.7 The Effectiveness of Chemical Antimicrobials against Endospores and Mycobacteria