1. Foundations in Microbiology
PowerPoint to accompany
Foundations in Microbiology
Fifth Edition
Talaro
Chapter 11
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. Physical and Chemical Control of Microbes
Chapter 11

3. Control of microbes
Physical and chemical methods to destroy or reduce microbes in a given area
Physical – heat and radiation
Chemical – disinfectants and antiseptics

4. Relative resistance of microbes
Highest resistance
Bacterial endospores
Moderate resistance
Bacteria with resistant vegetative cells:
Pseudomonas sp.
Mycobacterium tuberculosis
Staphylococcus aureus
Protozoan cysts
Some viruses (naked more resistant than enveloped)
Least resistance
most bacterial vegetative cells
Fungal spores
Enveloped viruses
Yeast
Protozoan trophozoites

5. Terms
Decontamination - The destruction, removal, or reduction in number of undesirable microbes
Sepsis - The growth of microorganisms in the tissues
Asepsis - Techniques that prevent the entry of microorganisms into sterile tissues
Antiseptic - Chemicals applied to body surfaces to destroy or inhibit vegetative pathogens

6. Terms
Sterilization – a process that destroys all viable microbes, including viruses & endospores (autoclave and radiation)
Disinfection – a physical or chemical agent that destroys vegetative pathogens, not endospores, on inanimate objects (bleach, boiling water)
Sanitization – any cleansing technique that mechanically removes microbes (soaps and detergents)
Degermation – reduces the number of microbes from living tissue (surgical hand scrub)

7. Fig. 11.1

8. Microbial death
Involves permanent loss of reproductive capability, even under optimum growth conditions

9. Factors that influence action of antimicrobial agents:
Number of microbes
Nature of microbes in the population (young cells die more quickly)
Temperature & pH of environment
Concentration or dosage of agent
Mode of action of the agent
Presence of solvents, organic matter, or inhibitors

10. Factors that influence the rate at which microbes are killed by antimicrobial agent

11. Cellular targets of control
Cell wall
Cell membrane
Cellular synthetic processes (DNA, RNA)
Proteins

12. Surfactants inserting into the lipid bilayer, alter permeability, cause leakage both in and out of the cell

13. a) The native state is maintained by bonds that create active sites to fit the substrate. Agents denature by breaking 2o and 3o bonds
c) Random bonding and incorrect folding

14. Selecting a workable method of microbial control
Practical concerns
Does the application require sterilization? Or is disinfection adequate?
Is the item to be reused?
Can the item withstand heat, pressure, radiation, or chemicals?
Is the method suitable?
Will the agent penetrate to the necessary extent?
Is the method cost- and labor-efficient & is it safe?

15. Methods of Physical Control
Heat
Cold temperatures
Desiccation
Radiation
Filtration

16. 1. Heat Moist heat – use of hot water or steam
Mode of action – denaturation of proteins, destruction of membranes & DNA
sterilization
autoclave 15 psi/121oC/10-40min (raise the temp of steam by increasing the pressure)
intermittent sterilization – unpressurized steam at 100oC min for 3 days
disinfection
Pasteurization <100oC for seconds; kills Salmonella, Listeria & overall microbe count
Boiling at 100oC for 30 minutes to destroy non-spore-forming pathogens

17. Sterilization using steam under pressure
The Autoclave

18. Dry heat using higher temperatures than moist heat, can also sterilize, less efficient that moist heat
incineration – oC combusts & dehydrates cells (limited to metals, ex. loop)
dry ovens – oC- coagulate proteins, not suitable for plastics/paper

19. Dry heat- Incineration
Shield prevents splattering of microbial samples during flaming

20. 2. Cold temperatures Microbistatic – slows the growth of microbes
refrigeration 0-15oC & freezing <0oC
Pathogens can survive several months
used to preserve food, media and cultures
-70oC to -135oC can preserve cultures of bacteria and viruses for long periods of time

21. 3. Desiccation
gradual removal of water from cells, leads to metabolic inhibition
not effective microbial control – many cells retain ability to grow when water is reintroduced
A valuable way to preserve foods

22. 4. Radiation
Defined as energy emitted from atomic activities and dispersed at high velocity through matter or space

23. 4. Radiation
Ionizing radiation – ejects orbital electron from an atom causing ions to form
Deep penetrating power, breaks DNA
gamma rays, X-rays, cathode rays
used to sterilize medical supplies & food products

24. 4. Radiation
Nonionizing radiation: Ultraviolet Rays – excites atoms by raising them to a higher energy state, leads to the formation of abnormal bonds
Little penetrating power to sterilize air, water and solid surfaces
UV light creates thymine pyrimidines dimers, which interfere with replication

25. Dislodges electron from molecules
Excites electron-abnormal bonds form
A solid barrier cannot be penetrated by nonionizing radiation

26. Formation of pyrimidine dimers by the action of UV radiation
Pyrimidine bases=
Thymine and cystosine
Dimers prevent that segment from correctly replicating or transcribing

27. An Ultraviolet (UV) treatment system for disinfection of water

28. 5. Filtration
physical removal of microbes by passing a gas or liquid through filter
used to sterilize heat sensitive liquids & air in hospital isolation units & industrial clean rooms

29. Filtration
Scanning electron micrograph of filter showing relative size of pores and bacteria trapped on surface (8um to 0.2um)

30. Chemical control Halogens Phenolics Chlorhexidine Alcohols
Hydrogen peroxide
Detergents & soaps
Heavy metals
Aldehydes

31. Halogens (used for disinfection for 200 yrs)
Chlorine – Cl2, hypochlorites (chlorine bleach), chloramines
Denaturation of proteins by disrupting disulfide bonds
Can be sporicidal
Iodine - I2, iodophors (Betadine)
Denature proteins
Milder medical & dental degerming agents, disinfectants, ointments
Less susceptible to inactivation by organic material

32. 2. Phenolics
Phenolics-one or more aromatic carbon rings with additional functional groups
Disrupt cell membranes & precipitating proteins; bactericidal, fungicidal, virucidal, not sporicidal
Lysol
triclosan- antibacterial additive to soaps

33. All contain basic aromatic ring, but differ in the types of additional compounds

34. 3. Chlorhexidine Hibiclens, Hibitane
A surfactant & protein denaturant with broad microbicidal properties
Not sporicidal
Used as skin degerming agents for preoperative scrubs, skin cleaning & burns
Mildness, low toxicity and rapid action

35. 4. Alcohols
Colorless hydrocarbons with one or more -OH functional groups
Ethyl or isopropyl alcohol in solutions of 50-95%. At 50% or greater concentration dissolves cell membrane lipids
70% proteins coagulate
100% dehydrates
Act as surfactants dissolving membrane lipids and coagulating proteins of vegetative bacterial cells, fungi, and enveloped viruses
Skin degerming agent. Not sporicidal

36. 5. Hydrogen peroxide (H2O2)
A colorless, caustic liquid that decomposes in the presence of light into water and oxygen gas
Weak (3%) to strong (25%)
Produce highly reactive hydroxyl-free radicals that damage protein & DNA while also decomposing to O2 gas – toxic to anaerobes
Strong solutions are sporicidal

37. 6. Detergents & soaps
Quaternary ammonia cpds act as surfactants that alter membrane permeability of some bacteria & fungi
Positively charged detergent
Not sporicidal
Soaps- mechanically remove soil and grease containing microbes
Alkaline cmpds made by combining the fatty acids in oils with sodium or potassium salts
Weak microbicides

38. Detergents are polar molecules with charged head and uncharged tail
A common quarternary ammonium detergent

39. Graph showing effects of hand scrubbing

40. 7. Heavy metals- (relatively high atomic weight: mercury, silver, and gold)
Solutions of silver & mercury kill vegetative cells in low concentrations by inactivating proteins
Oligodynamic action-the property of having antimicrobial effects in exceedingly sm. amts
Not sporicidal
Bind to functional groups of proteins and inactivate them

41. A pour plate inoculated with saliva
Contains silver and mercury

42. 8. Aldehydes
Organic substances bearing a reducing functional group on terminal carbon
Glutaraldehyde & formaldehyde kill by alkylating protein & DNA
glutaraldehyde in 2% solution (Cidex) used as sterilant for heat sensitive instruments, high-level disinfectant
formaldehyde - disinfectant, preservative, toxicity limits use

43. Gases & aerosols
Ethylene oxide, propylene oxide, betapropiolactone & chlorine dioxide
Strong alkylating agents, sporicidal
Sterilizing inanimates
Ethylene oxide is the gas used in chemiclaves
Reactions with functional groups of DNA and proteins, therefore, blocks both DNA replication and enzymatic actions

44. Sterilization Using Gas
An automatic ethylene oxide (ETO) sterilizer. Machine equipped with gas canisters containing ETO and carbon dioxide, chamber to hold items, and ways to evacuate and introduce air

46. Table 11.7

47. Fig. 11.1