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Microbial Control. Terminology for Microbial Control 0 Sterilization- removal or destruction of all forms of microbial life 0 Commercial sterilization-

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Presentation on theme: "Microbial Control. Terminology for Microbial Control 0 Sterilization- removal or destruction of all forms of microbial life 0 Commercial sterilization-"— Presentation transcript:

1 Microbial Control

2 Terminology for Microbial Control 0 Sterilization- removal or destruction of all forms of microbial life 0 Commercial sterilization- subjects canned food to only enough heat to destroy the endospores of Clostridium botulinum 0 Disinfection- is the destruction of vegetative pathogens on a surface, usually with chemicals 0 Spores and viruses are not necessarily destroyed 0 Antisepsis- is the chemical disinfection of living tissue, such as skin or mucous membranes

3 Terminology for Microbial Control 0 Asepsis- is the absence of pathogens on an object or area, as in antiseptic surgery 0 Degerming (degermation)- is the removal of transient microbes from the skin by mechanical cleansing or by antiseptic 0 Sanitation- is the reduction of microbial populations on objects to safe public health levels 0 A biocide or germicide- kills microorganisms 0 Fungicides kill fungi, virucides kill viruses 0 Suffix – cide means the killer of a specified microorganism 0 Suffix- stat used in this way indicates only that the substance inhibits – for example bacteriostasis

4 Rate of Microbial Death 0 Bacterial populations killed by heat or chemicals tend to die at constant rates—for example, 90% every 10 minutes. Plotted logarithmically, these figures form straight descending lines.

5 Factors that influence effectiveness of an antimicrobial treatment: 0 1. Number of microbes 0 -more cells, more time needed to kill all 0 2. Environmental influences 0 -organics often inhibit chemical agents (blood, feces, vomit) 0 -temperature (disinfectants work better in warm temperatures) 0 -pH (heat is more effective in an acid pH)

6 0 3. Time of exposure 0 -Chemical antimicrobials require a certain amount of exposure; same agent may need longer on resistant organisms or spores 0 -with heat, lower temps require longer to kill 0 4. Microbial characteristics 0 -resistance genes, protective structures 0 (e.g.capsules) etc. can inhibit action 0 -bioflims prevent penetration Factors that influence effectiveness of an antimicrobial treatment:

7 Type and Age of Microbe 0 Bacteria- susceptible to protein denaturing BUT mycobacteria is not because of its hydrophobic coat 0 Growth cycles- physiologically young bacteria(early in growth cycle) susceptible to heat 0 Endospores more resistant to heat the older they get

8 Properties of Materials: 0 Plastic and rubber- not heat tolerant 0 Cutting edges of surgical instruments- no moisture or corrosive chemicals 0 Edges can become pitted due to rust and corrosion, microbes can hide there 0 Fabrics- no chemical disinfection; some too fragile

9 Actions of Microbial Control Agents 0 1. Alteration of membrane permeability 0 The plasma membrane controls the passage of nutrients and wastes into and out of the cell. 0 Damage to the plasma membrane causes: 0 leakage of cellular contents 0 interferes with cell growth. 0 = Leak lysis, death

10 Actions of Microbial Control Agents 0 2. Damage to proteins and Nucleic Acids 0 Enzymes and other proteins are essential for cell function 0 Denatures proteins 0 Enzymes (no reactions) 0 Proteins necessary for bacteria metabolism 0 Hydrogen bonds are broken 0 Covalent bonds are also broken 0 3. Damage to nucleic acids 0 Prevent replication, transcription, or translation

11 Physical Methods of Microbial Control 0 -to disinfect objects, food, and solutions common methods: 0 -Temperature: kill or inhibit growth 0 Heat 0 Low Temps. 0 -Filtration: physical removal 0 -Desiccation: inhibit growth 0 -Osmotic pressure 0 -Radiation: kill

12 Methods involving Heat: 0 Heat: Common food preservation 0 Denatures protein (changes shape) 0 Thermal Death Point (TDP) = lowest temp at which all microbes in liquid suspension will be killed in 10 min 0 Thermal Death Time (TDT)= minimal length of time for all microbes in liquid suspension to be killed at given temp 0 *Both are different for different species due to microbial variation in heat tolerance 0 Decimal Reduction Time (DRT) = Time in minutes in which 90% of bacteria at a given temperature will be killed

13 Methods involving Heat: 0 1. Moist heat will always kill faster than dry heat at the same temperature 0 Kills microbes by coagulation of cell proteins 0 A. Boiling (100°C) kills vegetative forms of bacterial pathogens, many viruses, and fungi within 10 minutes 0 Some mo’s and viruses are resistant 0 Endospores (up to 20 hrs.) and some viruses (30 minutes) survive boiling for longer times.

14 Methods involving Heat: 0 B. Autoclaves 0 Moist Heat (steam) and pressure for sterilization 0 Achieves higher temps. than boiling 0 Preferred method (sealed chamber, air is exhausted, and steam under pressure is injected) for all materials that can withstand it 0 Kills all organisms and their endospores in about minutes 0 An autoclave is shown in Figure 1.1 and 1.2

15 Autoclave Figure 1.1 Figure 1.2 Autoclave tape

16 Methods involving Heat: 0 C. Pasteurization 0 Louis Pasteur 0 Mild Heating 0 Kills most pathogens 0 Kills bacteria that cause spoilage 0 Preserves taste in product 0 Lowers bacterial numbers

17 Methods involving Heat: 0 2. Dry Heat 0 Kills by burning to ashes or by oxidation 0 Flaming- we use this on loops in labs 0 Incineration- burning of contaminated paper 0 Hot air sterilization 0 Hot ovens 0 Mainly used for items not suitable for autoclaving 0 Oily substances, powders 0 Large amounts of glassware

18 Low Temperature 0 Lower temp inhibits growth, rapid freezing limits moisture (bacteriostatic) 0 Refrigerator temperatures (0° to 7°C) slow the metabolic rate of microbes; however 0 Psychrotrophic species still grow slowly. 0 Some organisms grow at temperatures slightly below freezing, but microbes at the usual temperatures of freezer compartments are completely dormant.

19 Filtration 0 Liquids 0 Heat- sensitive materials 0 Small pores prevent passage of bacteria 0 High-efficiency particulate air filters (HEPA) 0 Operating rooms 0 Special clean rooms 0 Masks 0 Used with solutions for: renal dialysis, heart bypass machines, I.V.’s 0 Catch particles autoclaves miss

20 Desiccation 0 Microbes require water for growth, and adequately dried (desiccated) foods will not support their growth, therefore inhibiting growth 0 Absence of Water 0 Lyophilization- rapid freeze drying 0 Used for blood products, serum products, enzymes, cultures 0 Avoids ice crystal formation; cells burst when water expands

21 Osmotic Pressure 0 High salt or sugar concentrations cause water to leave the cell; this is an example of osmosis. 0 Generally, molds and yeasts resist osmotic pressures better than bacteria.

22 Radiation 0 Ionization Radiation 0 includes X rays, gamma rays, and high-energy electron beams 0 very short wavelengths and high levels of energy 0 Penetrate deeply 0 Ionizes water to form hydroxyl radicals 0 These destroy cell components, especially DNA 0 Kills: vegetative cells, viruses, most endospores with adequate exposure 0 Applications: food preservation, sterilization of pharmaceuticals, medical supplies, mail

23 Radiation 0 Nonionizing radiation 0 Have a longer wavelength and less energy 0 Ultraviolet (UV) light is the common example 0 Causes the formation of thymine dimers, which interferes with DNA replication and formation of mRNA. 0 UV lamps are used in hospitals and in food service 0 This method does not sterilize, but it does reduce bacterial growth 0 Penetrating power is very low, so any type of covering protects microbes. 0 Sunlight has some weak antimicrobial effects (biocidal), but the wavelengths of sunlight are too long to work well.

24 Types of Chemical Agents 0 1. Phenols and Phenolics 0 A. Phenol (carbolic acid) 0 Irritating to skin and mucous membranes 0 Bad odor 0 Rarely used today 0 B. Phenolics 0 Chemicals derived from phenol 0 Chemically altered to make it less irritating and more effective 0 Damages plama mbs., inactivates enzymes, denature proteins 0 Often used as disinfectants as they remain active in the presence of organic matter

25 Types of Chemical Agents 0 C. Bisphenols 0 contain 2 phenolic groups connected by a bridge 0 Hexachlorophene 0 pHisoHex is an example 0 Prescription antibacterial lotion 0 Used in nurseries to control gram + bacteria 0 Skin bacteria: Staphylococcus and Streptococcus 0 Triclosan 0 Found in antibacterial soap 0 Effective against G+ and G- bacteria

26 Types of Chemical Agents 0 2. Biguanides 0 Chlorhexidine is an example 0 Hibiclens soap 0 Used on skin and mucous membranes 0 Similar to phenolics but less toxic 0 Disrupt plasma mb. 0 Broad spectrum 0 Effective against most vegetative bacteria and fungi, but not against endospores and many viruses. 0 Damaging to eyes

27 Types of Chemical Agents 0 3. Halogens- Effective alone or in compounds 0 A. Iodine (I 2 ) 0 One of the oldest and most effective 0 Very effective on: all bacteria, many endospores, fungi and some viruses 0 Combines with amino acids in proteins and denatures proteins 0 Alters plasma mb. 0 Negative Aspects 0 Staining 0 Sometimes irritating to the skin 0 May trigger allergies 0 Applications 0 Skin disinfection, wound treatment, water treatment

28 Types of Chemical Agents 0 B. Chlorine (Cl 2 ) 0 Action: forms hypochlorus acid with water → oxidizing agent, denatures proteins 0 Broad spectrum: bacteria, fungi, some endospores, some viruses 0 Positive aspects: -effective against all vegetative cells including Mycobacterium 0 -cost effective 0 Negative aspects: -action inhibited by organics 0 -can form carcinogenic compounds 0 Applications: water and sewage treatment, surface and instrument disinfection 0 Sodium hypochlorite (NaClO): Is active ingredient of bleach

29 Types of Chemical Agents 0 C. Alcohols- frequently used for skin degerming 0 Kill bacteria, fungi, but not endospores or naked viruses. 0 Act by denaturing proteins and disrupting cell membranes. 0 Used to mechanically wipe microbes off skin before injections or blood drawing, instrument disinfection 0 Not good for open wounds, because cause proteins to coagulate and leave bacteria unharmed 0 Ethanol (ethyl alcohol): Optimum concentration is 70%. 0 Isopropanol: Rubbing alcohol 0 Better disinfectant than ethanol 0 Usual concentration is 90% 0 Also cheaper and less volatile.

30 Types of Chemical Agents 0 5. Heavy metals and their compounds 0 Oligodynamic action- Very tiny amounts are effective 0 Includes-silver, mercury, copper, zinc 0 Bind sulfur groups causing inactivation or denaturing of proteins 0 A. Silver: 0 1% silver nitrate used to protect infants against gonorrheal eye infections until recently. 0 B. Mercury 0 Organic mercury compounds like merthiolate and 0 mercurochrome are used to disinfect skin wounds. 0 C. Copper 0 Copper sulfate is used to kill algae in pools and fish tanks (fungicidal, algicidal) 0 D. Zinc 0 Used in mouthwashes 0 Superficial fungal and bacterial infections

31 Types of Chemical Agents 0 6. Surface-Acting Agents 0 Disrupt plasma membrane & denature proteins 0 Decrease surface tension 0 Include soaps and detergents 0 Washing with soap breaks up the oily film that covers skin and allows microbes and dirt to be washed away 0 7. Quaternary Ammonium Compounds 0 Widely used surface active agents 0 Denature proteins & disrupt cell membranes 0 Cationic (positively charge) detergents 0 Effective against gram positive bacteria, less effective against gram-negative bacteria. 0 Also destroy fungi, amoebas, and enveloped viruses.

32 Types of Chemical Agents 0 8. Aldehydes 0 These can act very effectively against microbes 0 Inactivate proteins 0 Action: cross-link (thus inactivate) nucleic acids and proteins 0 High activity (sterilization) 0 biocidal including endospores 0 Positive aspects 0 achieves sterilization 0 Negative aspects 0 unstable 0 -toxic 0 -volatile with noxious fumes 0 Applications: specimen preservation (embalming), vaccine sterilization

33 Types of Chemical Agents 0 9. Gaseous Sterilizers 0 Chemicals that sterilize in a chamber similar to an autoclave. 0 Denature proteins, by replacing functional groups with alkyl groups 0 A. Ethylene Oxide 0 Kills all microbes and endospores, but requires exposure of 4 to 18 hours. 0 Toxic and explosive in pure form. 0 Highly penetrating. 0 Most hospitals have ethylene oxide chambers to sterilize mattresses and large equipment.

34 Types of Chemical Agents Peroxygens 0 Oxidize cellular components 0 A. Hydrogen Peroxide 0 Common household antiseptic 0 Not good for open wounds because quickly broken down by catalase present in human cells 0 used in deep wounds because it releases oxygen as it breaks down, which makes conditions unfavorable for anaerobic bacteria 0 Effective in disinfection of inanimate objects (kills endospores) 0 Sporicidal at higher temperatures 0 Used by food industry and to disinfect contact lenses

35 Types of Chemical Agents 0 B. Benzoyl Peroxide 0 Main ingredient in many acne treatments 0 May be used in treating wound infections caused by anaerobes 0 C. Peracetic Acid 0 One of the most effective liquid sporicides available 0 Sterilant : 0 Kills bacteria and fungi in less than 5 minutes 0 Kills endosporesand viruses within 30 minutes 0 Used widely in disinfection of food and medical instrument because it does not leave toxic residues


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