Controlling Microbial Growth

Sterilization

Kills all microbes including endospores

Disinfection

Kills vegetative microbes (not endospores)

Antisepsis

Disinfection of living tissue

Degerming

Mechanical removal of microbes

Sanitization

Reduces microbial numbers to safe levels

-cide

Kills microbes

-stasis

Inhibits microbial growth

Bactericidal

Kills bacteria

Bacteriostatic

Inhibits bacterial growth

Membrane damage

Alters permeability causing leakage and death

Protein damage

Denatures proteins disrupting function

DNA damage

Prevents replication and function

Moist heat

Kills by denaturing proteins using steam (more effective)

Dry heat

Kills using hot air (less effective)

Pasteurization

Mild heat to reduce microbial numbers

Autoclave

Uses steam under pressure to sterilize

Decimal reduction time (D)

Time required to kill 90% of microbes

Low D value

Faster microbial killing

High D value

Slower microbial killing

Cold

Slows growth but does not effectively kill microbes

Psychrotrophs

Microbes that can grow at low temperatures

Filtration

Removes microbes by physical barrier

Desiccation

Drying that can leave microbes dormant

Osmotic pressure

High salt/sugar removes water from cells

Ionizing radiation

High-energy radiation that damages DNA

UV radiation

Causes DNA mutations leading to death

Microwaves

Do not effectively kill microbes

Phenolics

Damage cell membranes (ex: Lysol)

Bisphenols

Disrupt microbial membranes (ex: triclosan)

Halogens

Oxidize cellular components (ex: iodine, chlorine)

Alcohols

Denature proteins and dissolve membranes (~70% most effective)

Heavy metals

Denature proteins (ex: silver, mercury)

Surfactants

Soaps that remove microbes but do not kill well

Quaternary ammonium compounds

Disrupt membranes, effective against Gram +

Aldehydes

Inactivate proteins and DNA

Gaseous sterilizers

Kill microbes using toxic gases (ex: ethylene oxide)

Peroxygens

Oxidize cell components (ex: hydrogen peroxide)

Initial population size

Larger populations take longer to kill

Environmental factors

Biofilms, dirt, and fluids protect microbes

Exposure time

Longer exposure increases killing effectiveness

Gram-negative bacteria

More resistant due to outer membrane

Mycobacterium

Resistant due to waxy cell wall

Lipid-enveloped viruses

More sensitive to disinfectants