Sterilization, Disinfection, and Antisepsis

Question 1

Cross-infection:

Answer 1

Transmission of infectious agents among

patients and staff in a clinical environment

Question 2

Cross-infection control: l

Answer 2

Management strategies for risk control

Question 3

Cross-infection risks in dentistry

Possible sources of infection in the dental care setting:

Answer 3

Patients with infectious disease

Patients in the prodromal or convalescent stage of infection

Healthy (or asymptomatic) carriers of disease-causing organisms

Environmental sources: airborne organisms or biofilms in waterlines or on equipment or instruments

Question 4

Universal precautions:

Answer 4

All patients are treated as though

they are a potential source of infectious pathogens.

Question 5

Airborne Routes
dust vs aerosol borne?
examples?
when is aerosol increased?

Answer 5

Examples of dust-borne routes:
Staphylococcus aureus from skin scales
Clostridium tetani from environmental dust
these and other organisms released from solid surfaces
sources: skin scales, wound dressings, solid surfaces

Examples of aerosol routes:
large droplets (classified as contact)
droplet nuclei
sources: speaking, sneezing, all intraoral procedures.
Massive increase when using ultrasonic scaling, air-rotor, air/water syringe.

Question 6

Prevention of aerosol transmission

Answer 6

1. Elimination or limitation of organisms at source

2. Interruption of transmission

Question 7

Contact Routes, preventions

Answer 7

person-to-person:
direct spread from person-to-person by hands and clothes or fomites (towels, etc.); large droplets (classified as contact)
prevention: hand washing, gloves, and protective clothing

equipment: dental instruments, chairs, impression materials
prevention : 
sterilization of instruments
use of disposals
disinfection of dental materials
environmental hygiene
defining zones in the dental operatory
disposal of infected waste

Fluids
dental water supplies
prevention: flushing water supply lines, using sterile water, and using biocide in water

Question 8

Parenteral Spread of Cross-Infection
sources
innoculation
prevention

Answer 8

Sources: blood, saliva, and secretions
Inoculation: via eye, skin breach, mucous membrane, sharps injury
prevention: training in use and disposal of sharps, hepatitis B vaccination, wearing gloves, dressing wounds

Question 9

sterilization

Answer 9

– destruction of all microbial forms (including bacterial spores)

Question 10

disinfection
agents of this? mainly?
used on?
levels?

Answer 10

– destruction of most microbial forms
– disinfectants
• agents, usually chemical, used for disinfection
• usually used on inanimate objects
• high-level, intermediate-level, low-level

Question 11

antisepsis

Answer 11

– Inhibition or elimination of microbes on living tissue
– antiseptics
• chemical agents that kill or inhibit growth of microorganisms when
applied to tissue

Question 12

sanitization

Answer 12

– reduction of microbial population to levels deemed safe (based
on public health standards)

Question 13

Antimicrobial agents

Answer 13

• agents that kill microorganisms or inhibit
their growth
• -cidal agents kill
• -static agents inhibit growth

Question 14

The Pattern of Microbial Death

Answer 14

• microorganisms are not killed instantly
• population death usually occurs exponentially
• microorganisms are considered to be dead when they are unable to reproduce in conditions that normally support their reproduction

Question 15

rate of microbial killing with time

Answer 15

Once the population has been greatly reduced the rate of killing may slow due to resistant individuals.

Question 16

Conditions Influencing the Effectiveness of Antimicrobial Agent Activity

Answer 16

• population size
• population composition
• concentration or intensity of an antimicrobial agent
• duration of exposure
• temperature
• local environment (e.g. pH, viscosity, etc.)

Question 17

The Use of Physical Methods in Control

Answer 17

• heat
• low temperatures
• filtration
• radiation

Question 18

• moist heat

Answer 18

– effective against all types of microorganisms
– degrades nucleic acids, denatures proteins, and
disrupts membranes

Question 19

• dry heat sterilization

Answer 19

– less effective, requiring higher temperatures and
longer exposure times
– oxidizes cell constituents and denatures proteins

Question 20

Measuring heat-killing efficiency, values?

Answer 20

• thermal death time (TDT)
– shortest time needed to kill all microorganisms in a suspension at a specific temperature and under defined conditions

• decimal reduction time (D or D value)
– time required to kill 90% of microorganisms or spores in a sample at a specific temperature

Question 21

Z value

Answer 21

– increase in temperature
required to reduce D to
10% of original value

Question 22

Autoclaves

Answer 22

type of moist heat
– used to kill endospores efficiently
– use saturated steam under pressure to reach temperatures above boiling

Question 23

Moist heat- pasteurization, milk?

Answer 23

– controlled heating at temperatures well below boiling
– reduces total microbial population and thereby increases shelf life of treated material

Pasteurization of milk
•flash pasteurization (high temperature short-term – HTST)
–72oC for 15 seconds then rapid cooling
•ultrahigh-temperature (UHT) sterilization
–140 to 150oC for 1 to 3 seconds

Question 24

Low Temperatures (freezing and refrigeration)

Answer 24

• freezing
– stops microbial reproduction due to lack of liquid water
– some microorganisms killed by ice crystal disruption of cell membranes
• refrigeration
– slows microbial growth and reproduction

Question 25

Filtration

Answer 25

• reduces microbial population or sterilizes solutions of heat-sensitive materials by removing microorganisms
• also used to reduce microbial populations in air

Question 26

Filtering liquids, types of filters?

Answer 26

• depth filters
– thick fibrous or granular filters that remove microorganisms by physical screening, entrapment, and/or adsorption
• membrane filters
– porous membranes with defined pore sizes that remove microorganisms primarily by physical screening

Question 27

Filtering air tools

Answer 27

• surgical masks

* high-efficiency particulate air (HEPA) filters

Question 28

Radiation types

Answer 28

UV and ionizing

Question 29

ultraviolet (UV) radiation

Answer 29

– limited to surface sterilization because UV radiation
does not penetrate glass, dirt films, water, and other
substance

Question 30

ionizing radiation

Answer 30

– penetrates deep into objects
– destroys bacterial endospores; not always effective against viruses
– used for sterilization and pasteurization of antibiotics, hormones, sutures, plastic disposable supplies, and food

Question 31

Phenolics
commonly used where?
mechanism?
problems?

Answer 31

phenol, hexochlorophene
• commonly used as laboratory and hospital disinfectants (Lysol is a mixture of phenolics)
• act by denaturing proteins and disrupting cell membranes
• tuberculocidal, effective in presence of organic material, and long lasting
• disagreeable odor and can cause skin irritation

Question 32

Alcohols
work on?
mechanism?
concentration?

Answer 32

ethanol, isopropanol
• bactericidal, fungicidal, but not sporicidal
• inactivate some viruses
• denature proteins and possibly dissolve membrane lipids
• 60%-90% in water (cidal activity drops sharply when diluted below 50% concentration)

Question 33

Halogens

Answer 33

contain fluorine, chlorine, bromine, iodine

Question 34

Iodine
primary use?
mechanism? 
high concentrations? 
issues? 
iodophores?

Answer 34

• skin antiseptic
• oxidizes cell constituents and iodinates proteins
• at high concentrations may kill spores
• skin damage, staining, and allergies can be a problem
• iodophore (iodine complexed with organic carrier)

Question 35

Chlorine
mechanism? 
important where? 
can/cannot destroy? 
carcinogen?

Answer 35

• oxidizes cell constituents
• important in disinfection of water supplies and swimming pools, used in dairy and food industries, effective household disinfectant
• destroys vegetative bacteria and fungi, but not spores
• can react with organic matter to form carcinogenic compounds

Question 36

Heavy Metals

Answer 36

• e.g., ions of mercury, silver, arsenic, zinc, and copper
• effective but usually toxic
• combine with and inactivate proteins; may also precipitate proteins

Question 37

Quaternary Ammonium

Compounds

Answer 37

cetylpyridium chloride, benzalkonium chloride
• detergents
– organic molecules with hydrophilic and hydrophobic ends
– act as wetting agents and emulsifiers

• cationic detergents are effective disinfectants
– kill most bacteria, but not Mycobacterium tuberculosis or endospores
– safe and easy to use, but inactivated by hard water and soap

Question 38

Aldehydes
reactivity?
spores?
mechanism?

Answer 38

• highly reactive molecules
• sporicidal and can be used as chemical sterilants
• combine with and inactivate nucleic acids and proteins

Question 39

Sterilizing Gases
used for?
-cidal towards?
mechanism?

Answer 39

ethlyene oxide, betaproprionelactone
• used to sterilize heat-sensitive materials
• microbicidal and sporicidal
• combine with and inactivate proteins

Question 40

Spaulding Inanimate Objects Classification

Answer 40