Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings PowerPoint ® Lecture Slide Presentation prepared by Christine L. Case M I C R O B I O L O G Y a n i n t r o d u c t i o n ninth edition TORTORA  FUNKE  CASE 7 The Control of Microbial Growth

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Control of Microbial Growth  Sepsis refers to microbial contamination.  Antisepsis: chemical method for disinfection directed at living tissue  The chemical is called an antiseptic  Asepsis is the absence of significant contamination.  Aseptic means that an object or area is free of pathogens  Aseptic surgery techniques prevent microbial contamination of wounds.

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Terminology  Sterilization: Removal of all microbial life  Commercial sterilization: Killing C. botulinum endospores  Disinfection: Removal of pathogens  Antisepsis: Removal of pathogens from living tissue  Degerming: Removal of microbes from a limited area  Sanitization: Lower microbial counts on eating utensils  Biocide/Germicide: Kills microbes  Bacteriostasis: Inhibiting, not killing, microbes

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Effectiveness of Antimicrobial Treatment  Depends on:  Number of microbes  Environment (organic matter, temperature, biofilms)  Time of exposure  Microbial characteristics Figure 7.1b

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Actions of Microbial Control Agents  Alternation of membrane permeability  Damage to proteins  Damage to nucleic acids

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Moist Heat vs. Dry Heat  Heat appears to kill microorganisms by denaturing their enzymes; inactivates them  Moist heat: kills microorganisms primarily by the coagulation of proteins (breaking hydrogen bonds to change their structure)  Boiling, autoclave  Dry heat: kills by oxidation effects  Flaming: sterilizing inoculating loops

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Physical Methods of Microbial Control  Filtration removes microbes  Low temperature inhibits microbial growth  Refrigeration  Deep freezing  Lyophilization  High pressure denatures proteins  Desiccation prevents metabolism  Osmotic pressure causes plasmolysis

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Physical Methods of Microbial Control  Pasteurization reduces spoilage organisms and pathogens  Equivalent treatments  63°C for 30 min  High temperature, short time: 72°C for 15 sec  Ultra high temperature: 140°C for <1 sec  Thermoduric organisms survive

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Chemical Methods of Microbial Control  Principles of effective disinfection  Concentration of disinfectant  Organic matter  pH  Time

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Chemical Methods of Microbial Control  Evaluating a disinfectant  Disk-diffusion method Figure 7.6