1/17/2016 Control of microbial growth began ~100 years ago Microbes following the discovery that microbes caused disease Lister and Semmelweis were the first to develop microbial control practices-aseptic surgery Invisible Invaders Before that time,10% Amazing Allies of surgical deaths and 25%of delivering mothers deaths were due to infections. During the American Chapter 7 Civil War,a surgeon The Control of Microbial Growth may have cleaned his scalpel on his boot sole between incisions. Terminology of Microbial Control Microbial Control Terminology Sterilization-a process that destroys all living microbes, including viruses and endospores:microbicidal Learning Objectives Commercial sterilization:food is heated enough to destroy endospores of Clostridium botulinum-absolute sterility would degrade the food Define the following key terms related to microbial control: Complete sterilization may not be required in many settings.such as a fork or drinking glass in a restaurant sterilization,disinfection,antisepsis, Aim:to prevent the spread of possible pathogens degerming,sanitization,biocide, Disinfection-a process to destroy vegetative pathogens germicide,bacteriostasis,and asepsis (not endospores)on inanimate objects Antisepsis:disinfectant treatment applied to living tissue Antiseptic:disinfectants applied directly to living tissue
1/17/2016 1 Invisible Invaders Amazing Allies Chapter 7 The Control of Microbial Growth Control of microbial growth began ~100 years ago following the discovery that microbes caused disease Lister and Semmelweis were the first to develop microbial control practices - aseptic surgery Before that time, 10% of surgical deaths and 25% of delivering mothers deaths were due to infections. During the American Civil War, a surgeon may have cleaned his scalpel on his boot sole between incisions. Learning Objectives Terminology of Microbial Control g j Define the following key terms related to microbial control: sterilization, disinfection, antisepsis, degerming, sanitization biocide sanitization, biocide, germicide, bacteriostasis, and asepsis Sterilization – a process that destroys all living microbes, including viruses and endospores; microbicidal Commercial sterilization: food is heated enough to destroy Microbial Control Terminology endospores of Clostridium botulinum - absolute sterility would degrade the food Complete sterilization may not be required in many settings, such as a fork or drinking glass in a restaurant Aim: to prevent the spread of possible pathogens Di i f ti Disinfection – a t d t t ti th process to destroy vegetative pathogens (not endospores) on inanimate objects Antisepsis: disinfectant treatment applied to living tissue Antiseptic: disinfectants applied directly to living tissue
1/17/2016 Microbial Control Terminology trol of Mic obinl Growth oe2 w.w..oe before an injection Sanitization-any cleansing technique that mechanically lowers the microbial count to safe public health levels and minimizes the chance of spreading disease Biocide.germocide.or bacteriocide:treatments that kill microbes:fungicide,virucide Bacteriostasis:treatments that inhibit growth of the bacteria Sepsis:indicates bacterial contamination Asepsis:absence of bacterial contamination Rate of Microbial Death treated with ant Learning Objectives die at a constant rate. A Microbial Death Curve plotted Describe the patterns of microbial death caused by treatments with microbial 28hg2osdcosionraeaihroie control agents 2
1/17/2016 2 Degerming – mechanical removal of microbes, which reduces their number, such as swabbing the skin before an injection Microbial Control Terminology Sanitization – any cleansing technique that mechanically lowers the microbial count to safe public health levels and minimizes the chance of spreading disease Biocide, germocide, or bacteriocide: treatments that kill microbes; fungicide, virucide Bacteriostasis: treatments that inhibit growth of the bacteria Sepsis: indicates bacterial contamination Asepsis: absence of bacterial contamination Learning Objectives Rate of Microbial Death g j Describe the patterns of microbial death caused by treatments with microbial control agents When bacterial populations are heated or treated with antimicrobial chemicals, they die at a constant rate. A Microbial Death Curve plotted logarithmically shows a constant death rate as a straight line
1/17/2016 Plotting the typical microbial death curve logarithmically(red line)results in a straight line. Microbial Exponential Death Rate: 1.000.000 TABLE 7.2 An Example 60 Time(min) Deaths per Minute Number of Survivors 0 1,000,000 3.0 600,000 1 900,000 100,000 90,000 10,.000 0,000 100.000 3 9000 1000 7 900 100 Time(min) A microbial death 5 90 10 9 3 mi he cells would 9 ance betwee 100 000 and the baseline. Several factors influence the death rate: Number of microbes:more there are the longer it takes Environmental influences: organic matter inhibits action of chemical antimicrobials biofilms -temperature fats and proteins are protective Time of exposure:longer time for more resistant microbes Time(min) Microbial characteristics:such as (b)Logarithmic plotting(red)reveals that if the rate of killing is the same,it will take longer to kill all members of a endospore or not larger population than a smaller one,whether using heat or chemical treatments
1/17/2016 3 Plotting the typical microbial death curve logarithmically (red line) results in a straight line. r of ser of s One log decrease = 90% of population log10 of numbe r surviving cell s Arithmetic numb e surviving cell skilled Time (min) A microbial death curve plotted arithmetically (blue line) is impractical: at 3 minutes the population of 1000 cells would only be a hundredth of the graphed distance between 100,000 and the baseline. Several factors influence the death rate: • Number of microbes: more there are the longer it takes • Environmental influences: - organi tt i hibit ti f ic matter inhibits action of chemical antimicrobials - biofilms - temperature - fats and proteins are protective • Time of exposure: longer time for more resistant microbes • Microbial characteristics: such as endospore or not r of ls sterile surgical equipment log10 of numbe surviving cel l Time (min) (b) Logarithmic plotting (red) reveals that if the rate of killing is the same, it will take longer to kill all members of a larger population than a smaller one, whether using heat or chemical treatments
1/17/2016 Actions of Microbial Control Agents Alteration of Membrane Permeability Plasma membrane is the target of many Learning Objectives antimicrobial agents. The membrane regulates Describe the effects of microbial passage of nutrients control agents on cellular structures into and wastes out of the cell. Damage to the lipids and content to leak into the surroundina medium and interferes with growth. Damage to Proteins and rily Nucleic Acids Physical Methods of Microbial Control Enzyme activity requires a 3D- structure that is maintained by Learning Objectives chemical bonds connecting portions of the polypeptide. Compare the effectiveness of moist heat (boiling,autoclaving.pasteurization)and akage by h dry heat ing to prote denaturati Describe how filtration,low temperatures. high pressure,desiccation,and osmotic enzyme. pressure suppress microbial growth. Nucleic acids (DNA,RNA)are damoged by heat and chemicals Explain how radiation kills cells which is often lethal for the cell as it can no longer replicate or carry out normal functions
1/17/2016 4 Learning Objectives Actions of Microbial Control Agents g j Describe the effects of microbial control agents on cellular structures Alteration of Membrane Permeability Plasma membrane is the target of many antimicrobial agents. The membrane regulates passage of nutrients into and wastes out of the cell. Damag p e to the lipids and phospholipids causes the cytoplasmic content to leak into the surrounding medium and interferes with growth. Damage to Proteins and Nucleic Acids Enzymes are primarily protein and are vital for cellular activities. Enzyme activity requires a 3Dstructure that is maintained by chemical bonds connecting portions of the polypeptide. The bonds are susceptible to breakage by heat or chemicals leading to protein denaturation, enzyme restructuring, or binding. All of which inactivate the en mzy e. Nucleic acids (DNA, RNA) are damaged by heat and chemicals, which is often lethal for the cell as it can no longer replicate or carry out normal functions. Learning Objectives Physical Methods of Microbial Control • Compare the effectiveness of moist heat (boiling, autoclaving, pasteurization) and dry heat • Describe how filtration, low temperatures, high pressure, desiccation, and osmotic pressure suppress microbial growth. • Explain how radiation kills cells
1/17/2016 As early as the stone age,humans have been When selecting the method of microbial control, using some type of physical method of microbial control to preserve food. you must consider what else besides the microbe will the method affect. Drying and Salting were probably the most common early techniques. Heat will inactivate vitamins or antibiotics in a solution Repeated heating damages laboratory and hospital equipment. Economic considerations:using presterilized,disposable plasticware versus washing and resterilization of glassware. Heat:Mode of Action and Relative Thermal Death Measurements Effectiveness Heat resistance varies among different microbes and Moist heat is expressed as TDP. .lower temperatures and shorter Thermal Death Point (TDP)-the lowest temperature at which all microbes in a particular exposure time liquid will be killed in 10 minutes coaqulation and denaturation of proteins Length of time to sterilize is expressed as TDT. Thermal Death Time (TDT)-minimal length of Dry heat time for all bacterial in a particular liguid to be killed at a given temperature .moderate to high temperatures .dehydration Third concept related to heat resistance: Decimal reduction time(DRT)-the time,in .alters protein structure minutes,in which 90%of the population of .incineration bacteria at a given temperature will be killed
1/17/2016 5 As early as the stone age, humans have been using some type of physical method of microbial control to preserve food. Drying and Salting were probably the most common early techniques. When selecting the method of microbial control, you must consider what else besides the microbe will the method affect. • Heat will inactivate vitamins or antibiotics in a solution • Repeated heating damages laboratory and hospital equipment. • Economic considerations: using presterilized, disposable plasticware versus washing and resterilization of glassware. Heat: Mode of Action and Relative Effectiveness Moist heat •lower temperatures and shorter exposure time • coagulation and denaturation of proteins Dry heat • moderate to high temperatures • dehydration • alters protein structure •incineration Thermal Death Measurements Heat resistance varies among different microbes and is expressed as TDP. Thermal Death Point (TDP) – the lowest temperature at which all microbes in a particular liquid will be killed in 10 minutes Length of time to sterilize is expressed as TDT. Thermal Death Time (TDT) – minimal length of time for all bacterial in a particular liquid to be killed at a given temperature Third concept related to heat resistance: Decimal reduction time (DRT) – the time, in minutes, in which 90% of the population of bacteria at a given temperature will be killed