1. Using Chemicals to Destroy Microorganisms and Viruses
Chapter 5

2. Approaches to Control Control mechanisms either physical or chemical
May be a combination of both
Physical methods
Heat
Irradiation
Filtration
Mechanical removal
Chemical methods
Use a variety of antimicrobial chemicals
Chemical depends on circumstances and degree of control required

3. Approaches to Control Principles of control Sterilization Disinfection
Removal of ALL microorganisms
Sterile item is absolutely free of microbes, endospores and viruses
Can be achieved through filtration, heat, chemicals and irradiation
Disinfection
Eliminates most pathogens
Some viable microbes may exist
Disinfectants = used on inanimate objects and surfaces
Antiseptics = used on living tissues

4. Approaches to Control Principles of control Pasteurization
Brief heat treatment used to reduce organisms that cause food spoilage
Surfaces can also be pasteurized
Decontamination
Treatment to reduce pathogens to level considered safe to handle
Degerming
Mechanism uses to decrease number of microbes in an area
Particularly the skin (antiseptics)

5. Approaches to Control Principles of control Sanitized Preservation
Implies a substantially reduced microbial population
This is not a specific level of control
Preservation
Process used to delay spoilage of perishable items
Often includes the addition of growth-inhibiting ingredients

6. Approaches to Control Situational considerations
Microbial control methods are highly variable
Depends on situation and degree of control required
Daily life
Hospital
Microbiology laboratories
Food and food production facilities
Water treatment

7. Approaches to Control Daily life
Washing and scrubbing with soaps and detergents achieves routing control
Hand washing single most important step to achieving control
Soap acts as wetting agent
Aids in mechanical removal of microorganisms
Removes numerous organisms from outer layer of skin
Normal flora usually unaffected because it resides in deeper layers

8. Approaches to Control Hospitals
Minimizing microbial population very important
Due to danger of nosocomial infections
Patients are more susceptible to infection
Pathogens more likely found in hospital setting
Numerous organisms develop antimicrobial resistance due to high concentrations of antibiotics
Instruments must be sterilized to avoid introducing infection to deep tissues

9. Approaches to Control Microbiology laboratories
Use rigorous methods of control
To eliminate microbial contamination to experimental samples and environment
Aseptic technique and sterile media used for growth
Eliminates unwanted organisms
Contaminated material treated for disposal
Eliminates contamination of environment

10. Approaches to Control Food and food production facilities
Retention of quality enhanced through prevention of microbial growth and contamination
Achieved through physical removal and chemical destroying organisms
Heat treatment most common and most reliable mechanism
Irradiation approved to treat certain foods
Chemicals prevent spoilage
Risk of toxicity

11. Approaches to Control Water treatment facilities
Ensures drinking water is safe
Chlorine generally used to disinfect water
Can react with naturally occurring chemicals
Form disinfection by-products (DBP)
Some DBP linked to long-term health risks
Some organisms resistant to chemical disinfectants

12. Selection of Antimicrobial Procedure
Selection of effective procedure is complicated
Ideal method does not exist
Each has drawbacks and procedural parameters
Choice of procedure depends on numerous factors
Type of microbe
Extent of contamination
Number of organisms
Environment
Risk of infection
Composition of infected item

13. Selection of Antimicrobial Procedure
Type of microorganism
Most critical consideration
Is organism resistant or susceptible to generally accepted methods?
Resistant microbes include
Bacterial endospores
Resistant to heat, drying and numerous chemicals
Protozoan cysts and oocysts
Generally excreted in feces and cause diarrheal disease
Mycobacterium species
cell wall structure initiates resistance
Pseudomonas species
Can grow in presence of many chemical disinfectants
Naked viruses
Lack envelope and are more resistant to chemical killing

14. Bacterial endospores Protozoans
Clostridium botulinum – causes botulism, resists boiling, but autoclaving kills
Protozoans
Giardia lamblia and Cryptosporidium parvum
Cause digestive problems

15. Selection of Antimicrobial Procedure
Number of organisms initially present
Time it takes to kill it directly affected by population size
Large population = more time
Commercial effectiveness is gauged by decimal reduction time
a.k.a D value
Time required to kill 90% of population under specific conditions
Washing reduces time required to reach disinfection or sterilization

16. Selection of Antimicrobial Procedure
Environmental conditions
Environmental conditions strongly influence effectiveness
pH, temperature and presence of organic materials can increase or decrease effectiveness
Most chemicals are more effective at higher temperatures and lower pH
Effectiveness can be hampered by the presence of organism molecules
Can interfere with penetration of antimicrobial agent

17. Selection of Antimicrobial Procedure
Potential risk of infection
Medical items categorized according to potential risk of disease transmission
Critical items = come in contact with body tissues
Needles and scalpels
Semicritical instruments = contact mucous membranes but do not penetrate body tissues
Endoscope
Non-critical instruments = contact unbroken skin only
Show little risk of transmission
stethoscope

18. Selection of Antimicrobial Procedure
Composition of the item
Some sterilization and disinfection methods inappropriate for certain items
Heat inappropriate for plastics and other heat sensitive items

19. Heat as Control Heat treatment most useful for microbial control
Relatively fast, reliable, safe and inexpensive
Heat can be used to sterilize or disinfect
Methods include
Moist heat
Dry heat

20. Heat as Control Moist heat
Destroys through irreversible coagulation of proteins
Moist heat includes
Boiling
Pasteurization
Pressurized steam

21. Heat as Control Boiling (100° C) Pasteurization
Destroys most microorganisms and viruses
Not effective means of sterilization
Does not destroy endospores
Pasteurization
Pasteur developed to avoid spoilage of wine
Does not sterilize but significantly reduces organisms
Used to increase shelf life of food
Most protocols employ HTST method
Heated to 72°C and held for 15 seconds
Other protocol UHT
Heated to 140°C - 150°C, held for several seconds then rapidly cooled

22. Heat as Control Pressurized steam
Autoclave used to sterilize using pressurized steam
Heated water  steam  increased pressure
Preferred method of sterilization
Achieves sterilization at 121°C and 15psi in 15 minutes
Effective against endospores
Flash autoclaving sterilizes at 135°C and 15psi in 3 minutes
Prions destroyed at 132°C and 15psi for 4.5 hours

23. Heat as Control Dry heat Not as effective as moist heat
Sterilization requires longer times and higher temperatures
200°C for 1.5 hours vs. 121°C for 15 minutes
Incineration method of dry heat sterilization
Oxidizes cell to ashes
Used to destroy medical waste and animal carcasses
Flaming laboratory inoculation loop incinerates organism
Results in sterile loop

24. Other Physical Methods of Control
Heat sensitive materials require other methods of microbial control
Filtration
Irradiation
High-pressure treatment

25. Other Physical Methods of Control
Filtration
Membrane filtration used to remove microbes from fluids and air
Liquid filtration
Used for heat sensitive fluids
Membrane filters allow liquids to flow through
Traps microbes on filter
Depth filters trap microbes using electrical charge
Filtration of air
High efficiency particulate air (HEPA) filter removes nearly all microbes from air
Filter has 0.3µm pores to trap organisms

26. Other Physical Methods of Control
Radiation
Electromagnetic radiation
Energy released from waves
Based on wavelength and frequency
Shorter wavelength, higher frequency = more energy
Range of wavelength is electromagnetic spectrum
Radiation can be ionizing or non-ionizing

27. Other Physical Methods of Control
Ionizing radiation
Radiation able to strip electrons from atoms
Three sources
Gamma radiation
X-rays
Electron accelerators
Causes damage to DNA and potentially to plasma membrane
Used to sterilize heat resistant materials
Medical equipment, surgical supplies, medications
Some endospores can be resistant

28. Other Physical Methods of Control
Ultraviolet radiation
Non-ionizing radiation
Only type to destroy microbes directly
Damages DNA
Causes thymine dimers
Used to destroy microbes in air, drinking water and surfaces
Limitation
Poor penetrating power
Thin films or coverings can limit effect

29. Other Physical Methods of Control
High pressure processing
Used in pasteurization of commercial foods
Does not use high temperatures
Employs high pressure
Up to 130,000 psi
Destroys microbes by denaturing proteins and altering cell membrane permeability

30. Chemicals as Control Chemicals can be used to disinfect and sterilize
Called germicidal chemicals
Reacts with vital cell sites
Proteins
DNA
Cell membrane

31. Chemicals as Control Potency of chemicals Sterilants =
Formulations generally contain more than one antimicrobial agent
Regulated by
FDA
Antiseptics
EPA
Disinfectants
Germicidal agents grouped according to potency
Sterilants =
Destroy all microorganisms
High-level disinfectants
Destroy viruses and vegetative cells,
Not endospores
Intermediate-level disinfectants
Kill vegetative cells fungi, most viruses,
Low-level disinfectants
Removes fungi, vegetative bacteria and enveloped viruses,
Not mycobacteria, naked viruses or endospores

32. Chemicals as Control Selecting appropriate chemical Points to consider
Toxicity
Benefits must be weighed against risk of use
Activity in presence of organic material
Many germicides inactivated in presence of organic matter
Compatibility with material being treated
Liquids cannot be used on electrical equipment

33. Chemicals as Control Selecting appropriate chemical Points to consider
Residue
Residues can be toxic or corrosive
Cost and availability
Storage and stability
Concentrated stock relieves some storage issues
Environmental risk
Is germicidal agent harmful to environment

34. Chemicals as Control Classes of chemicals
Germicides represent a number or chemical families
Alcohols
Aldehydes
Biguanides
Ethylene oxide
Halogens
Metals
Ozone
Peroxides
Phenolics
Quaternary ammonium compounds

35. Preservation of Perishable Products
Preservation extends shelf-life of many products
Chemicals are often added to prevent or slow growth of microbes
Other methods include
Low temperature storage
Freezing
Reducing available water

36. Chemicals as Control Chemical preservatives
Numerous chemicals are used as preservatives
Formaldehyde, Quats, and phenols
Weak organic acids often used as food preservatives
Benzoic, ascorbic and propionic acids
Used in bread, cheese and juice
Mode of action
Alter cell membrane function
Interfere with energy transformation
Nitrates and nitrites used in processed meats
Inhibits germination of endospores and growth of vegetative cells
Have been shown to be potent carcinogen

37. Chemicals as Control Low temperature storage
Microbial growth is temperature dependent
Low temperatures slow down or stop enzymatic reactions of mesophiles and thermophiles
Some psychrophiles still able to grow
Freezing as means of food preservation
Essentially stops microbial growth
Irreversibly damages cell
Kills up to 50% of microbes
Remaining cells still pose potential threat

38. Chemicals as Control Reducing water availability
Decreasing water availability accomplished by salting or drying food.
Addition of salt increases environmental solutes
Causes cellular plasmolysis
Numerous bacteria can continue to grow in high salt environments
Staphylococcus aureus can survive in high salt concentrations
Desiccation or drying is often supplemented by other methods
Salting
Lyophilization (freeze drying)
Widely used to preserve foods like coffee, milk and meats