Disinfectants lecture

Question 1

Action of Antimicrobial Agents: Alteration of cell walls and membranes

Answer 1

– Cell wall maintains integrity of cell
– When damaged, cells burst because of osmotic
effects
– Cytoplasmic membrane controls passage of
chemicals into and out of cell
– When damaged, cellular contents leak out
– Non-enveloped viruses more tolerant of harsh
conditions

Question 2

Action of Antimicrobial Agents: Damage to proteins and nucleic acids

Answer 2

– Protein function depends on 3-D shape
– Extreme heat or certain chemicals denature
protiens
– Chemicals, radiation, and heat can alter/destroy
nucleic acids
– Produce fatal mutants
– Halt protein synthesis through action on RNA

Question 3

Ideally, agents should be?

Answer 3

– Inexpensive
– Fast-acting
– Stable during storage
– Capable of controlling microbial growth while being harmless to humans, animals, and objects

Question 4

Factors Affecting the Efficacy of Antimicrobial Methods: Site to be treated

Answer 4

– Harsh chemicals and extreme heat cannot be
used on humans, animals, and fragile objects
– Microbial control based on site of medical
procedure
– Temperature
– pH
– Residual organic matter

Question 5

Factors Affecting the Efficacy of Antimicrobial

Methods: Relative susceptibility of microorganisms

Answer 5

– Germicides classified as high, intermediate, or low
effectiveness
– High—kill all pathogens, including endospores
– Intermediate—kill fungal spores, protozoan cysts,
viruses, pathogenic bacteria
– Low—kill vegetative bacteria, fungi, protozoa, some
viruses

Question 6

Heat-Related Methods: Effects of high temperatures does what?

Answer 6

– Denature proteins
– Interfere with integrity of cytoplasmic membrane and cell wall and cell wall
– Disrupt structure and function of nucleic acids

Question 7

Heat-Related Methods: Moist heat

Answer 7

– Used to disinfect, sanitize, and sterilize
– Denatures proteins and destroys cytoplasmic membranes
– More effective than dry heat
– Methods of microbial control using moist heat
– Boiling
– Autoclaving
– Pasteurization
– Ultra high-temperature sterilization

Question 8

Moist heat: Boiling

Answer 8

– Kills vegetative cells of bacteria and fungi,
protozoan trophozoites, most viruses
– Boiling time is critical
– Different elevations require different boiling times
– Endospores, protozoan cysts, and some viruses
can survive boiling

Question 9

Moist heat: Autoclaving

Answer 9

– Pressure applied to boiling water prevents steam from escaping
– Boiling temperature increases as pressure increases
– Autoclave conditions – 121ºC, 15 psi, 15 min

Question 10

Moist heat: Pasteurization

Answer 10

– Used for milk, ice cream, yogurt, and fruit juices
– Not sterilization
  * Heat-tolerant microbes survive
– Pasteurization of milk
  * Batch method
  * Flash pasteurization
  * Ultrahigh-temperature pasteurization

Question 11

Heat-Related Methods: Dry heat

Answer 11

– Used for materials that cannot be sterilized with
moist heat
– Denatures proteins and oxidizes metabolic and
structural chemicals
– Requires higher temperatures for longer time than
moist heat
– Incineration is ultimate means of sterilization

Question 12

Refrigeration and Freezing

Answer 12

– Decrease microbial metabolism, growth, and reproduction
– Chemical reactions occur more slowly at low temperatures
– Liquid water not available
– Psychrophilic microbes can multiply in
refrigerated foods
– Refrigeration halts growth of most pathogens
– Slow freezing more effective than quick freezing
– Organisms vary in susceptibility to freezing

Question 13

Desiccation and Lyophilization

Answer 13

– Drying inhibits growth because of removal of water
– Lyophilization used for long-term preservation of microbial cultures
– Prevents formation of damaging ice crystals

Question 14

Osmotic Pressure

Answer 14

– High concentrations of salt or sugar in foods to inhibit growth
– Cells in hypertonic solution of salt or sugar lose water
– Fungi have greater ability than bacteria to survive hypertonic environments

Question 15

Radiation main points

Answer 15

– Ionizing radiation
– Wavelengths shorter than 1 nm
– Ejects electrons from atoms to create ions
– Ions disrupt hydrogen bonding, oxidize double covalent bonds, and create hydroxide ions
– Hydroxide ions denature other molecules (DNA)
– Electron beams – effective at killing but do not penetrate well
– Gamma rays – penetrate well but require hours to kill microbes

Question 16

Radiation: Nonionizing radiation

Answer 16

– Wavelengths greater than 1 nm
– Excites electrons, causing them to make new
covalent bonds
– Affects 3-D structure of proteins and nucleic acids
– UV light causes pyrimidine dimers in DNA
– UV light does not penetrate well
– Suitable for disinfecting air, transparent fluids, and
surfaces of objects

Question 17

Phenol and Phenolics

Answer 17

– Intermediate- to low-level disinfectants
– Denature proteins and disrupt cell membranes
– Effective in presence of organic matter
– Remain active for prolonged time
– Commonly used in health care settings, labs, and homes
– Have disagreeable odor and possible side effects

Question 18

Alcohols main points

Answer 18

– Intermediate-level disinfectants
– Denature proteins and disrupt cytoplasmic membranes
– More effective than soap in removing bacteria from hands
– Swabbing of skin with 70% ethanol prior to injection

Question 19

Halogens are?

Answer 19

– Intermediate-level antimicrobial chemicals
– Believed to damage enzymes via oxidation or by denaturation
– Widely used in numerous applications
– Iodine tablets, iodophores, chlorine treatment, bleach, chloramines, and bromine disinfection

Question 20

Oxidizing Agents are?

Answer 20

– Peroxides, ozone, and peracetic acid
– Kill by oxidation of microbial enzymes
– High-level disinfectants and antiseptics
– Hydrogen peroxide can disinfect and sterilize surfaces
– Not useful for treating open wounds because of catalase activity
– Ozone treatment of drinking water
– Peracetic acid is effective sporocide used to sterilize equipment

Question 21

Surfactants are?

Answer 21

– “Surface active” chemicals
– Reduce surface tension of solvents
– Soaps and detergents
– Soaps have hydrophilic and hydrophobic ends
– Good degerming agents but not antimicrobial
– Detergents are positively charged organic surfactants
– Quats
– Low-level disinfectants
– Ideal for many medical and industrial applications

Question 22

Heavy Metals are?

Answer 22

– Heavy-metal ions denature proteins
– Low-level bacteriostatic and fungistatic agents
– 1% silver nitrate to prevent blindness caused by N. gonorrhoeae
– Thimerosal used to preserve vaccines
– Copper controls algal growth

Question 23

Aldehydes are?

Answer 23

– Compounds containing terminal –CHO groups
– Cross-link functional groups to denature proteins and inactivate nucleic acids
– Glutaraldehyde disinfects and sterilizes
– Formalin used in embalming and disinfection of rooms and instruments

Question 24

Gaseous Agents – Ethylene oxide are?

Answer 24

– Microbicidal and sporicidal gases used in closed chambers to sterilize items
– Denature proteins and DNA by cross-linking functional groups
– Used in hospitals and dental offices
– Disadvantages
  * Can be hazardous to people
  * Often highly explosive
  * Extremely poisonous
  * Potentially carcinogenic