1. Control of Microorganisms by Physical and Chemical Agents
Chapter 7
Control of Microorganisms by Physical and Chemical Agents

2. Definition of Frequently Used Terms
sterilization
destruction or removal of all viable organisms
disinfection
killing, inhibition, or removal of pathogenic organisms
disinfectants
agents, usually chemical, used for disinfection
usually used on inanimate objects

3. More definitions… sanitization antisepsis
reduction of microbial population to levels deemed safe (based on public health standards)
antisepsis
prevention of infection of living tissue by microorganisms
antiseptics
chemical agents that kill or inhibit growth of microorganisms when applied to tissue

4. Antimicrobial agents
agents that kill microorganisms or inhibit their growth
-cidal agents kill
-static agents inhibit growth

5. -cidal agents -cide suffix indicating that agent kills germicide
kills pathogens and many nonpathogens but not necessarily endospores
include bactericides, fungicides, algicides, and viricides

6. -static agents -static suffix indicating that agent inhibits growth
include bacteriostatic and fungistatic

7. Conditions Influencing the Effectiveness of Antimicrobial Agent Activity
population size
larger populations take longer to kill than smaller populations
population composition
microorganisms differ markedly in their sensitivity to antimicrobial agents

8. More conditions… concentration or intensity of an antimicrobial agent
usually higher concentrations or intensities kill more rapidly
duration of exposure
longer exposure  more organisms killed

9. More Conditions… temperature
higher temperatures usually increase amount of killing
local environment
many factors (e.g., pH, viscosity and concentration of organic matter) can profoundly impact effectiveness
organisms in biofilms are physiologically altered and less susceptible to many antimicrobial agents

10. The Use of Physical Methods in Control
heat
low temperatures
filtration
radiation

11. Moist Heat 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
degrades nucleic acids, denatures proteins, and disrupts membranes

12. The Autoclave or Steam Sterilizer
Figure 7.3

13. 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

14. Dry Heat Sterilization
less effective than moist heat sterilization, requiring higher temperatures and longer exposure times
items subjected to oC for 2 to 3 hours
oxidizes cell constituents and denatures proteins

15. Dry Heat Incineration
bench top incinerators are used to sterilize inoculating loops used in microbiology laboratories
Figure 7.4

16. Low Temperatures freezing refrigeration
stops microbial reproduction due to lack of liquid water
some microorganisms killed by ice crystal disruption of cell membranes
refrigeration
slows microbial growth and reproduction

17. Filtration
reduces microbial population or sterilizes solutions of heat-sensitive materials by removing microorganisms
also used to reduce microbial populations in air

18. Filtering liquids depth filters membrane filters
thick fibrous or granular filters that remove microorganisms by physical screening, entrapment, and/or adsorption
membrane filters
porous membranes with defined pore sizes that remove microorganisms primarily by physical screening

19. Figure 7.7

20. Ultraviolet (UV) Radiation
limited to surface sterilization because it does not penetrate glass, dirt films, water, and other substances
has been used for water treatment
Figure 7.9

21. Phenolics commonly used as laboratory and hospital disinfectants
act by denaturing proteins and disrupting cell membranes
tuberculocidal, effective in presence of organic material, and long lasting
disagreeable odor and can cause skin irritation

22. Alcohols bactericidal, fungicidal, but not sporicidal
inactivate some viruses
denature proteins and possibly dissolve membrane lipids

23. Halogens - Chlorine oxidizes cell constituents
important in disinfection of water supplies and swimming pools, used in dairy and food industries, effective household disinfectant
destroys vegetative bacteria and fungi, but not spores

24. Quaternary Ammonium Compounds

25. Sterilizing Gases used to sterilize heat-sensitive materials mattress
microbicidal and sporicidal
combine with and inactivate proteins

26. Figure 7.13

27. Chemotherapeutic Agents
chemicals that can be used internally to kill or inhibit the growth of microbes within host cells
their selective toxicity allows them to target the microbe without harming the host
most are antibiotics, chemicals synthesized by microbes that are effective in controlling the growth of bacteria