Sterilization, Disinfection, Decontamination

Question 1

Sterilization

Answer 1

Removing or killing of all microbes on an object or in any material

• killing means making microbes unable to grow or reproduce, even under most favorable growth conditions
• sterile means totally devoid of life

Question 2

What is the limiting requirement?

Answer 2

Destruction of bacterial endospores, the most resistant form of life

Question 3

Disinfection

Answer 3

Process of reduction or elimination of pathogenic microbes in or on materials so they are no longer a hazard
- implies that some living microbes may persist

Question 4

Disinfectants

Answer 4

Sanitizers, chemical agents used on inanimate objects

Question 5

Antiseptics

Answer 5

Relatively nontoxic chemical agents used on animals or people

Question 6

Decontamination

Answer 6

Same as disinfection but implies a broader role including inactivation or removal of microbial toxins and pathogens

Question 7

Germicide

Answer 7

Refers to an agent capable of killing most microbes rapidly

- agents may be bactericidal, sporicidal, fungicidal, or viricidal

Question 8

Bacteriostatic or fungistatic

Answer 8

Indicate that the antimicrobial agent is primarily inhibitory in its action

• prevent growth without killing
• agent may be -cidal against one species and -static against another

Question 9

What does the action of the cidal or static agent depend on?

Answer 9

• concentration
• pH
• temperature
• time of exposure

Question 10

Preservation

Answer 10

Prevention of multiplication of microorganisms in formulated products, including pharmaceuticals and foods

Question 11

Methods for preventing exposure to undesirable microbes

Answer 11

• mechanical removal: washing and scrubbing
• cooking food
• maintain normal flora

Question 12

Heat

Answer 12

Destroys microbes in 4 ways:

• boiling water or steam at 100 C: kills most pathogenic organsims, but is not sterilization
• dry heat
• steam under pressure
• pasteurization: controlled heating at a lower temp

Question 13

Autoclaving

Answer 13

Most effective and commonly used method to achieve sterilization

• temp of 121 C is attained when steam is at 15 psi pressure
• 15 minutes is effective for instrument sterilization, but longer times may be needed for media or other liquids

Question 14

Radiation

Answer 14

Used to sterilize medical materials

• UV light from lamps used to combat air-borne infections and contaminants (effective against vegetative cells, but some spores are resistant)
• ionizing radiation is commonly used to sterilize many items, including food and almost all disposable medical devices

Question 15

Filtration

Answer 15

Used to sterilize bacteriologic media, serum, injection fluids, and solutions or other heat sensitive substances

• filter with a pore size of 0.45 um or less will remove all bacteria (except mycoplasms) from solutions
• filters will not remove viruses and are used to separate bacteria from viruses for viral culture

Question 16

What are resistant to disinfectants and antiseptics?

Answer 16

Spores –> mycobacteria –> gram neg bacteria –> gram positive bacteria

Question 17

How do antiseptics and disinfectants differ from antibiotics?

Answer 17

• they have a broader spectrum of activity
• may have multiple targets in or on the bacterial cell (antibiotics have specific intracellular or cell envelope targets)

Question 18

Alcohols

Answer 18

• rapidly bactericidal, including many acid-fast organisms, but are not sporicidal
• widely used for hard-surface decontamination and skin antisepsis
• antimicrobial activity is optimal in the 60-90% range

Question 19

Ethylene oxide gas

Answer 19

• sporicidal: requires special equipment to sterilize and takes long exposure times
• is mutagenic and explosive, but is not harsh on sensitive instruments
• following EO gas sterilization a long aeration time is required

Question 20

Aldehydes

Answer 20

Glutaraldehyde: most bactericidal compound available
- broad spec activity against bacteria, spores, fungi, and viruses
- has good mycobactericidal activity, but exposure time is critical
- used for low-temp disinfection of endoscopes and surgical instruments
Formaldehyde: sporicidal, but requires a long exposure time
- mixed with alcohols it is the most effective instrument soak available

Question 21

Halogens

Answer 21

Chlorines, iodines

• sodium hypochlorite (bleach): hard surface decontamination
• aqueous or alcoholic solutions of iodine are rapidly bactericidal, sporicidal, and fungicidal, but they are unstable and associated with irritation and excessive staining
• iodophors: complexes of iodine with a solubilizing agent, are more stable but considered less active against spores and fungi

Question 22

Phenolic compounds

Answer 22

Used as antiseptics, disinfectants, and preservatives

• pheno is oldest known disinfectant, can cause chemical burns
• chloroxylenol is broad spec antimicrobial effective against bacteria, fungi, and viruses
• triclosan: used in antiseptic soaps and hand rinses, especially effective against gram-positives

Question 23

Quaternary ammonium compounds

Answer 23

Cationic detergenes

• nitrogenous cationic surface active agents used for preoperative disinfection of unbroken skin, application to mucosal membranes, disinfection of non-critical surfaces
• used for cleaning and deodorization
• not sporicidal, not mycobactericidal but have mycobacteristatic action

Question 24

Biguanide compounds

Answer 24

Detergents sometimes combined with quaternary ammoniums

• chlorhexidine: bactericidal with broad spec efficacy
• activity is pH dependent and reduced in presence of organic matter
• not mycobactericidal or sporicidal

Question 25

Peroxygens

Answer 25

Hydrogen peroxide

• used for disinfection and antisepsis
• broad spec activity (greater activity against gram-pos than gram-neg)
• bacterial expression of catalase or other peroxidases can increase tolerance
• higher concentrations and longer exposure time required for sporicidal activity

Question 26

Silver compounds

Answer 26

Used to prevent infection of burns and some eye infections

• silver nitrate
• silver sulfadiazine: combo of 2 antibacterial agents (Ag and sulfadiazine)

Question 27

Mercurials

Answer 27

No longer used as disinfectants, but still used as preservatives in pharmaceuticals, primarily vaccines

Question 28

Descending order of intrinsic resistance

Answer 28

• spores
• mycobacteria
• gram-neg
• gram-pos

Question 29

Acquired resistance

Answer 29

• mutation
• gene acquisition (plasmid, transposon): associated with metallic salts, such as mercury
• physiology adaptation: bacteria in biofilms have increased resistanceto antibiotics and disinfectants