o   destruction of endospores of Clostridium botulinum in canned food but not all endospores

§  Some thermophile endospores survive but can’t grow in canned foods due to room temp

o   absence of microorganisms from object or area

§  Air filters, UV lights, masks, gloves, sterile instruments all useful in achieving this

   Rate of Microbial Death

o   Microbes of a single type treated with antimicrobial agent die at constant rate

o   Microbial death curves can be constructed

§  Straight line if logarithm of population plotted versus time. thus the bacteria die at a constant rate

§  After 6 min of 90% dying/min 1 of 1 million microbes would be alive

o   Large populations take longer to kill

o   Factors affecting kill time

§  Bacterial load

§  Time of exposure

Mechanism of Action of Antimicrobial Agents

·         Kill in 2 ways

o   Disrupt integrity of cell

§  Cell wall maintains shape and integrity and protects from osmotic pressure

§  No wall à cell bursts

§  Water leaks in, cellular components leak out

§  These microbicidal agents also inactivate lipid enveloped viruses

·         Lipid envelope mediates attachment to host cell

·         Without envelope – no attachment or infection

·         Naked viruses much harder to inactivate (more resistant)

o   Disrupt cellular metabolism and reproduction by damaging proteins or nucleic acids

§  Proteins  have native conformation destroyed by heat and chemical agents

·         Denaturation – egg example

·         Denatured proteins – nonfunctional

DNA destruction – lethal

Factors to Consider in Choosing an Antimicrobial Agent

o   Nature of site to be treated

o   Susceptibility of microbes

o   Environmental conditions that apply to treatment

Nature of site to be treated

o   Instruments penetrating skin

§  High potential for infection

§  Critical items

§  Must be clean or sterile

o   Instruments touching mucous membranes or skin with out penetrating

§  Low potential for infection

§  Semi-critical items

§  Need to be clean and disinfected unless patient is immunocompromised

o   Items not touching membranes or skin

§  Non critical

§  Need to be cleaned and disinfected

                               Harsh chemicals or extreme heat cannot be used on humans, animals, sensitive material

·         Depends on microbe and physiological state

·         Dormant forms like endospores and protozoan cysts more resistant than vegetative cells

o   Antimicrobials have difficulty penetrating them

o   Actively  growing cells are more susceptible to killing than non-replicating cells because DNA, protein, and cell wall damage only affects growing cells

·         Mycobacteria are more resistant to killing because of lipid mycolates on cell wall

o   Difficult to penetrate

·         Spectrum

o   Endospores

o   Mycobacteria

o   Protozoan Cysts

o   Vegetative Protozoans

o   Gram-negative bacteria

o   Fungi

o   Non-enveloped viruses

o   Gram-positive bacteria

o   Enveloped viruses

Choose method to kill the most resistant microbe possible in population – should kill least in population

Environmental conditions that apply to treatment

§  Must be able to kill microbes under environmental conditions

·         Temperature

·         pH

·         Organic materials

·         Dirt

·         Grease

§  Organic matter, dirt, and grease

·         Can interfere with killing action

·         Must be cleaned to ensure contact

§  Antimicrobials more effective at low pH

§  Antimicrobials more effective in warm solutions

·         Reactions increase

§  Use at manufacturer’s recommended temperature and condition