Using Chemicals to Destroy Microorganisms and Viruses

1. Using Chemicals to DestroyMicroorganisms 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 • 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 • 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 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) • 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. Potency of chemicals 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, Not endospores Low-level disinfectants Removes fungi, vegetative bacteria and enveloped viruses, Not mycobacteria, naked viruses or endospores Chemicals as Control

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