Microbial Growth and Control PDF

PowerPoint® Lecture Presentations CHAPTER 5 Microbial Growth and Its Control © 2018 Pearson Education, Inc. Lecture Overview This lecture focuses on the control and the destruction of microorganisms by physical and chemical agents. This is a topic of great importance, because microorganisms may...

PowerPoint® Lecture Presentations CHAPTER 5 Microbial Growth and Its Control © 2018 Pearson Education, Inc. Lecture Overview This lecture focuses on the control and the destruction of microorganisms by physical and chemical agents. This is a topic of great importance, because microorganisms may have deleterious effects, such as food spoilage and disease. It is therefore essential to be able to kill or remove microorganisms from certain environments in order to minimize their harmful effects. Lecture objectives After this lecture and reading the text you should be able to: • compare and contrast the processes of disinfection, sanitization, antisepsis, and sterilization • compare the difficulties encountered when trying to kill endospores with those encountered when trying to kill vegetative cells • discuss the exponential pattern of microbial death • discuss the influence of environmental factors on the effectiveness of various agents used to control microbial populations • discuss the uses and limitations of various physical and chemical agents used to control microbial populations • describe the procedures used to evaluate the effectiveness of various antimicrobial agents 2 • discuss biological agents used to control microorganisms 3 Definition of Frequently Used Terms  sterilization  destruction or removal of all viable organismsmore extreme conditions than disinfection- only these are effective against endospores  disinfection  killing, inhibition, or removal of disease causing (pathogenic) organisms –but not endospores!  disinfectants  agents, usually chemical, used for disinfection  usually used on inanimate objects  e.g. ozone for drinking water, or chemicals for floors and table tops 4 More Definitions…   sanitization  reduction of microbial population to levels deemed safe (based on public health standards)- e.g. dry handwashing gel antisepsis  prevention of infection of living tissue by microorganisms  antiseptics  chemical agents that kill or inhibit growth of microorganisms when applied to tissue  e.g. Alcohol 60-85%, certain soaps 5 Alcohols, hydrogen peroxide and others can be antiseptic, disinfectants, sanitizers 6 or sterilants depending on concentration, length of exposure and delivery method. -cidal Agents -cide  suffix indicating that agent kills  germicide  kills pathogens and many nonpathogens but not necessarily endospores  include bactericides, fungicides, algicides, and viricides 7 -static Agents -static  suffix indicating that agent inhibits growth  include bacteriostatic and fungistatic 8 Chemical control of microbial growth e.g. some antibiotics e.g. formaldehyde e.g. soaps Environmental Limits on Microbial Growth  Temperature  pH  Osmolarity  Oxygen  Pressure 10 The Pattern of Microbial Death  microorganisms are not killed instantly  population death usually occurs exponentially  measure of agent’s killing efficiency  decimal reduction time – time to kill 90%  must be sure persister cells (viable but nonculturable (VBNC) condition) are dead  once they recover they may regain the ability to reproduce and cause infection 11 12 Controlling Microbial Growth  Microbes die at logarithmic rate  D-Value = time to kill 90% of cells 2 D-values = time to kill 99% of cells  Antimicrobial agents decrease D-value  Kills cells faster 13 Changes in Temperature  Growth rate increases with temperature  Proteins denature if temperature too high  Microbial  Psychrophiles   12°C - 45°C Thermophiles   Cold: O°C - 20°C Mesophiles   proteins adapted to temperature range: 40°C - 80°C Extreme thermophiles  65°C - 113°C 14 Response to Temperature  Heat shock response  Occurs at high end of temperature range  “Emergency” proteins produced  Help keep proteins from denaturing  Induced by many stressful conditions Heat  High salt concentrations  Arid conditions  15 Variations in Pressure  Barophiles  Adapted   up to 1,000 atm Barotolerant organisms  Grow  to high pressures at high, but not very high pressure Barosensitive organisms  Die  at high pressure e.g. most “typical” bacteria, all mammals 16 Changes in Water Activity  Solutes raise osmolarity  High osmolarity reduces available water  Osmotic pressure can burst membranes  Low osmotic pressure outside cell Mechanosensitive channels relieve stress  Release cell contents   High osmotic pressure outside cell Cells synthesize osmolytes  Increase internal osmolarity  17 Changes in Water Activity  Halophiles  Require high concentration of NaCl  2-4 M (10x seawater)  Live in salt seas 18 Changes in pH  Neutralophiles  Grow at pH 5 – 8  Include bacteria in gut  Acidophiles  Grow at pH 0 – 5 Some grow in stomach acid  Some in sulfuric acid springs   Alkalophiles  Grow  at pH 9 - 11 Found in soda lakes 19 Oxygen as Electron Acceptor  Aerobes – O2 is ultimate electron acceptor  Very strong electron acceptor  Can oxidize, damage proteins  Anaerobes  Reactive   oxygen species (ROS) produced Oxidize, damage proteins Microaerophiles  Can  tolerate low levels of O2 Catalase inactivates ROS 20 Physical Agents - Temperature  Pasteurization  63°C  for 30 minutes Flash Pasteurization  72°C  for 15 seconds Pasteurization treatments do NOT kill all cells Pasteurized food spoils eventually  Leaves food tasting normal   UHT – Ultra-High Temperature  150°C  for 3 seconds Sterilizes – all bacteria killed  Used for creamers 21 Pasteurization controlled heating at temperatures well below boiling  used for milk, beer, and other beverages  process does not sterilize but does kill pathogens present and slow spoilage by reducing the total load of organisms present  22 Physical Agents - Temperature + Pressure  Autoclave = steam cooker  121°C, 15 psi (2 atm) for 20 minutes  Kills all bacteria  Kills endospores  Clostridium botulinum   botulism Bacillus anthracis  anthrax 23 Steam Sterilization must be carried out above 100oC which requires saturated steam under pressure  carried out using an autoclave  effective against all types of microorganisms including spores  quality control - includes strips with Geobacillus stearothermophilus  24 Physical Agents – Other Methods  Cold temperature - refrigeration  Slows   growth, does not kill all bacteria Freezing Irradiation  UV,  X-rays, g-rays Filtration 25 26 27 © 2008 W.W. Norton & Company, Inc. MICROBIOLOGY 1/e 28 Chemical Agents  Disinfectants  Kill all microbes-not endospores  Destroys eukaryotic cells as well  Cannot be used inside patients  Bleach (chlorine), Betadyne (iodine)  Soap  Detergents 29  Triclosan is in everything! 30 Triclosan, caffeine, and nonylphenol concentration profiles for Boulder Creek, Colorado, showing downstream variations during spring runoff . Streamflow is from left to right. The increase in concentrations from site aWWTP to site 75 is the result of the discharge from a wastewater treatment plant (WWTP). Triclosan is an antimicrobial disinfectant used in many soaps. Caffeine is often used as an indicator of human wastewater contamination. Nonylphenol is a detergent metabolite. Going downstream 31 32 Chemical Agents  Antibiotics  Selectively  May not work on all species  Has  kills microbes minimal effect on eukaryotic cells Can be used inside patients  Interferes with bacterial-specific enzymes Cell wall synthesis  Bacterial ribosome  33 Penicillin    Many derivatives Blocks cell wall synthesis Growing bacteria lyse  Slow-growing bacteria take longer to die Weakening cell wall 34 Biological Agents  Probiotics  “Good”   bacteria Displace disease organisms from tissues Bacteriophage  “Phage”  Viruses that attack bacteria  Do not harm eukaryotes 35