Exam 1: Sterilization and Disinfection

Question 1

Sterilization

Answer 1

All forms of microbial life killed including spores.

Question 2

Disinfection

Answer 2

Most infectious agents killed on inanimate surfaces.

Generally fail to kill spores, mycobacteria, and hepatitis viruses.

Question 3

Sanitization

Answer 3

The overall lowering of the number of bacteria to safe levels.

Question 4

Antiseptics

Answer 4

Substances that kill or prevent growth of microorganisms on living tissue.

Effect on skin is temporary due to recolonization from pores and ducts.

Question 5

Pasteurization

Answer 5

Use of heat to kill certain pathogenic bacteria.

• 62° C for 30 minutes or 74° C for 3-5 minutes
• Includes Salmonella, Mycobacterium, Listeria, Strep, Brucella, Campylobacter
• Does not kills spores
• Reduces overall bacterial content by 97-99%

Question 6

Germicide

Answer 6

Agent that kills microoganisms.

Analogous to disinfectant/antiseptic.

• Bacteriocide ⇒ kills bacteria
• Sporicides ⇒ extends activity to spores
• Viricide ⇒ kills viruses
• Fungicide ⇒ kills fungi
• Tuberculocide ⇒ kills mycobacteria

Question 7

Pyrogens

Answer 7

Microbe-derived contaminants that cause fever when injected.

• Low MW
• Not removed by filtration
• Survive autoclaving
• Pyrogen free = never had microbial growth present
• Heating contaminated fluids ⇒ lysis and release of endotoxin
  
  • Sterilization by filtration better
• Ex. LPS from dead bacteria

Question 8

High Level

Germicides/Disinfectants

Answer 8

Effective against vegetative bacteria, fungi, viruses, AND spores.

May require prolonged contact time or high concentrations.

Question 9

Intermediate Level

Germicides/Disinfectants

Answer 9

Not effective against bacterial spores but effective against vegetative bacteria, fungi, and many viruses.

Question 10

Low Level

Germicides/Disinfectants

Answer 10

Effective against most vegetative bacteria, some fungi, and some viruses.

Limited in their activity.

Question 11

Order of Resistance

Answer 11

Descending order of resistance to disinfection/sterilization:

Question 12

Moist Heat

Answer 12

• Autoclaving ⇒ most common method of sterilization in hospitals
• Rapid & inexpensive
• Can penetrate clumps of organic material
• Steam under 15lbs/sq. in
• Temp of 121 °C for 15-20 minutes
• Best way to kill bacterial spores

Question 13

UV Radiation

Answer 13

• Causes nicks or thymine dimers in DNA
  
  • Inhibits transcription and replication
• Unable to penetrate liquids and solids
• Limited usefulness
• Most often used for airborne contamination
• Staph and spore-formers relatively UV-resistant

Question 14

Ethylene Oxide

Answer 14

• Gas used to sterilize surgical/medical equipment that cannot autoclave due to heat sensitivity
• Acts as alkyating agent
  
  • Adds alkyl group to amino groups of proteins and nucleic acids
• Can be sporicidal
• Can penetrate porous material
• Time required after treatment to allow residual ethylene oxide to aerate out
• Gas is toxic, flammable, and mutagenic

Question 15

Phenolic Compounds

Answer 15

• Intermediate to low level disinfectants
• Act by denaturing protein-membrane complexes
• Use limited to general housekeeping & noncritical items
• Remains active in presence of organics and after prolonged drying
• Absorbed through porous material ⇒ may irritate tissues
  
  • Not used on instruments that contact mucous membranes

Question 16

Quaternary Ammonium

Compounds

Answer 16

• Low level disinfectant
• Acts as “cationic detergents”
  
  • Dissociate to NH⁴⁺ that disrupts membrane phospholipids
• Poor activity against Gram ⊖
• No activity against spores or mycobacteria
• Inactivated by organic matter
• Use limited to noncritical items
• Ex:
  
  • Benzalkonium chloride ⇒ topical disinfectant
  • Cetylpyridinium chloride ⇒ mouthwashes

Question 17

Biquanides

Answer 17

“Chlorhexadine”

• Antiseptic used as surgical scrub, hand wash, and superficial skin wound cleaner
• Can be incorporated into catheters etc
• Structure & action similar to quaternary ammonium compounds
  
  • Cationic agents that disrupts membrane phospholipids

Question 18

Chlorine Compounds

Answer 18

• Releases free chlorine
  
  • Reacts with water ⇒ hypochlorous acid
  • Strong oxidizing agent
    
    • Inactivates proteins via sulfhydryl groups
• Intermediate level @ high concentrations
  
  • Used for spot disinfection
  • 1-5% bleach solutions ⇒ tuberculocidal & viricidal
    
    • But corrosive
• Low level @ low concentrations
  
  • Used to treat water

Question 19

Iodine Compounds

Answer 19

• Halogen that oxidizes protein sulfhydryl groups
• Low to intermediate level depending on concentration
• Iodine dissolved in 2% alcohol ⇒ tincture
  
  • Activity against most bacteria including mycobacteria
• Iodine + organic carrier ⇒ iodophore
  
  • Carrier slows release of free iodine
  • Increases effective time
  • Decreases toxicity
  • Ex. povidone iodine (Betadine)

Question 20

Alcohols

Answer 20

• Disrupts membranes & denatures proteins
• Ethyl & isopropyl alcohols @ 70% ⇒ intermediate level
  
  • Tuberculocidal
  • Limited action against some viruses
  • No activity against spores
• Useful as antiseptics
  
  • Rapidly drying
  • Inexpensive
  • No residue