Chapter 5 - Control of Microbial Growth

What is sterilization?

• The absolute removal or destruction of ALL microorganisms

What is disinfection?

• The destruction of most microbes including pathogens

  • doesn’t kill all microbes

What is antisepsis?

• The disinfection of skin or living tissue

  • uses normally less harsh treatments

What is degerming?

• Removal of most microbes from a limited areaWh

What is sanitization?

• Lowering microbial counts to a safe level to meet public health standards

What does the suffix -cide mean?

• An agent that kills microbes

What does the suffix -static or -stasis mean?

• An agent that stops the growth of microbes

What is asepsis?

• An area is free of significant contamination 

What does bactericidal mean?

• Kills microbes by destroying enzymes

How effective is boiling to destroy microbes? (1.2.1)

• Five minutes kills:

  • most pathogenic bacteria - not all endospores

  • most viruses

    • this is disinfection - not sterilization

How effective is pasteurization?

• Sufficient to eliminate pathogens + lower microbial #s to slow spoilage

What are the types of pasteurization? (3)

• Classic treatment - mild heating to 63 C for 30 min

• HTST (high temp, short time) - 72 C for 15 sec

• UHT (ultra high temp) - 140 C for 3 secs

What is autoclave? (1.1.1)

• Pressure (15 psi) and steam (121 C)

  • kills all endospores in 15 mins

    • best method for sterilization

What is autoclave used for? (3)

• Culture media

• Hospital instruments

• Hospital materials that withstand heat + moisture

What is direct flaming? (1.1)

• Dry heat sterilization

  • used in microbiology lab to sterilize inoculation needs + loops

What is incineration? (1.1)

• Dry heat sterilization

  • effective way to dispose of contaminated materials

What is hot air sterilization? (1.1)

• Dry heat sterilization

  • a drying oven - materials should stay at 170 C for 2 hrs

What is filtration? (1.1)

• A vacuum used to force liquid → a filter with very small pores

  • pores are too small for bacteria to pass

What is filtration used for? (1.3)

• Sterilizing temperature sensitive liquids

  • antibiotics

  • enzymes

  • some vaccines

What is air filtration used in? (1.1)

• Operating rooms to remove all microbes larger than 0.3 um 

  • High efficiency particulate air filters (HEPA)

What is the function of refrigeration? (1.1)

• Slows or stops microbial growth

  • bacteriostatic

What is the function of freezing? (1.2)

• Stops microbial growth

  • only a small portion or microbes will die

  • bacteriostatic

What is the function of high pressure? (1.2.1)

• Liquid suspensions are treated with it

  • kills many bacterial cells - bactericidal

  • doesn’t kill endospores 

    • not sterilization 

What is dessication?

• The removal of water (drying)

What is the function of dessication? (1.1)

• Slows or stops growth of microbes - but usually doesn’t kill

  • bacteriostatic

How is osmotic pressure bactericidal/static?

• Can kill some bacteria from the high concentrations of salts + sugars

What is the function of radiation?

• Destroys the DNA of microorganisms

What are the types of radiation + what are they used for? (2)

• X-rays + Gamma - penetrate materials

• UV + High energy electron beams - used on surfaces

How are microwaves used to disinfect materials? (1.1)

• Heat water to high temperatures - can be used to disinfect

  • don’t kill microorganisms directly

What is the process of the disk diffusion method? (3.1)

• Disk of filter paper is soaked in chemical disinfectant

• Placed on agar plate inoculated with bacteria

• Plate is incubated until bacteria grows

  • Zone of clearing determines effectiveness

What are phenols? (1.2)

• Compounds that disrupt plasma membranes and denature proteins (bactericidal)

  • Effective + remain active long after application

  • Suitable for disinfection of soiled surfaces 

What are biguanides? (1.1.2)

• Disinfectants that attack the plasma membrane - bactericidal

  • Chlorhexidine - controls microbes on skin + mucous membranes

    • persists up to 6 hrs

    • only kills some viruses, doesn’t destroy endospores

What is the function of a halogen? (1.1)

• Destroy proteins and membranes

  • used in disinfectants and antiseptics

What is the functionof chlorine?

• Forms hypochlorous acid in water - denatures enzymes

What is the function of iodine?

• Used as an antiseptic

What is the function of alcohols? (1.2)

• Denatures proteins + disrupts membranes

  • Kills bacteria + fungi

  • Doesn’t kill endospores + some viruses

What is silver nitrate used as?

• Eye drops for newborns - protects against gonorrheal opthalmia

What is silver sulfadiazine used for?

• Topical cream for burns

What are silver ions used for?

• Incorporated → bandages + catheters to slow growth of microbes

What is the function of copper sulfate?

• Inhibits algae in reservoirs

What is the function of mercuric chloride?

• used in paint to control mildew

What is the function of zinc chloride?

• Used as an antiseptic in mouthwashes

What is the function of regular soaps + detergents? (1.2.1)

• Important in the mechanical removal of microbes

  • Soap breaks up oily deposits + films

  • Water washes the deposits away w/ microbes

    • doesn’t work as a disinfectant or antiseptic

What are quaternary ammonium compounds (QUATS)? (1.2.1)

• Cationic detergents - kill most bacteria, fungi, and some viruses

  • don’t kill endospores

  • don’t kill some gram negative bacteria

    • some gram negative bacteria survive + grow well on Quats

What are gaseous chemosterilizers?

• Chemical gasses used for sterilization

What is ethylene oxide? (1.1)

• Germicidal - denatures proteins

  • kills all microbes (endospores + viruses included)

What are oxidizing agents?

• Agents used to oxidize and denature proteins

  • useful against anaerobic organisms

What are examples of oxidizing agents? (3.1)

• Hydrogen Peroxide - common antiseptic for wounds

• Ozone - used w/ chlorine to disinfect water

• Benzoyl peroxide - used as antiseptic on skin

  • kills anaerobic bacteria living in tissues