微生物学英文课件-Controlling Microbes.PPTVIP

Controlling Microbial Growth Antimicrobial Kills or prevent growth of microbes Microbiocidal Kills all microbes Sterilant Kills vegetative endospores Microbiostatic Only inhibits the growth of microbes Sterilization destroy all microbial life Disinfection reduces number of pathogens pose no danger of disease Decontamination renders contaminated surface safe to handle Antisepsis kills microorganisms on living tissue Microbial Death Rate Decimal reduction time D-value time required to kill 90% of cells Heat treatments temperature type of microorganism physiological state other substances Decimal Reduction Time Example: 1,000,000 (106) 1 minute = 90% killed 2 minutes = 100,000 (90%) 3 minutes = 10,000 4 minutes = 1,000 5 minutes = 100 6 minutes = 1 cell Sterilization Thermal death point lowest temperature kill all microorganisms in broth 10 minutes Thermal death time minimal time kill all microorganisms (sterilize) liquid suspension at given temperature Conditions that Affect Antimicrobial Activity Population density Larger number the more time Concentration Increase in concentration ? decreases in time Time exposure Increase exposure increases the number of killed Temperature Higher Temp. ? greater number killed Substrate Affect the efficiency of agent Microbial characteristics Susceptibility to different agents Mechanisms of Microbial Agents MODE OF ACTION Interferes with cellular components Cell membrane Cell wall Ribosomes Genetic material (DNA) Enzymes Cytosol Physical Controls Heat Moist boiling kills most vegetative cells, not sterile autoclave steam under pressure: 15 lbs./in2 at 121oC for 15 min. kills endospores Pasteurization kills certain microorganisms Bacteria Fungi Spores 5-10 min. 5-10 min. 5-10 min. 60-70oC 50-60oC 70-80oC Pasteurization Involves heating to temperatures below boiling for certain time periods (63-66oC for 30 minutes) Does not kill all microbes, but only those causing disease Reduces the numbers of microbes that cause food