Download Microbiology

THE TERMINOLOGY OF MICROBIAL
CONTROL
• Sterilization-removing ALL microbial life; heat
• Sterilant- a sterilizing agent
• Commercial sterilization- killing C. botulinum endospores in
food; used so food is not destroyed
• Disinfection- removing pathogens not including
endospore
• Antisepsis- removing pathogens from living tissue
• Degerming- mechanical removal of microbes from
a limited area; using an alcohol swab
• Sanitization- lowering microbial counts on eating
utensils to a public health safety number
THE TERMINOLOGY OF MICROBIAL
CONTROL
• Biocide/germicide- killing microbes
• Fungicide- kills fungi
• Virucide- inactivates viruses
• Bacteriostasis- inhibiting, not killing, microbes
• Sepsis- microbial contamination
• Asepsis-the absence of significant microbial
contamination
• Aseptic surgery techniques prevent microbial
contamination of wounds
RATE OF MICROBIAL DEATH
• Microbes die at a
constant rate.
• Each minute of
treatment kills 90%
of REMAINING
microbes.
EFFECTIVENESS OF TREATMENT
• Depends on:
•
•
•
•
Number of microbes
Environment (organic matter, temperature, biofilms)
Time of exposure
Microbial characteristics
ACTIONS OF MICROBIAL CONTROL
AGENTS
1. Alteration of membrane permeability- damages
lipids or proteins.
2. Damage to proteins- enzyme damage due
denaturation
3. Damage to nucleic acids- cell can no longer
replicate or carry on normal metabolic functions
QUESTION:
• Would a chemical microbial control agent that
affects plasma membranes affect humans? 7-3
PHYSICAL METHODS OF
MICROBIAL CONTROL
HEAT
• Thermal death point (TDP): lowest temperature at
which all cells in a culture are killed in 10 min
• Thermal death time (TDT): time during which ALL
cells in a culture are killed
• Decimal Reduction Time (DRT): Minutes to kill 90% of
a population at a given temperature
Figure 7.10 A comparison of the effectiveness of various antiseptics.
MOIST HEAT STERILIZATION
• Moist heat denatures proteins by breaking H bonds
• Types:
1. Boiling- can kill most bacterial pathogens and
viruses in 10 minutes; endospores up to 20 hours
2. Autoclave: steam under pressure; 15psi, 121C, 15
minutes; can kill endospores
• Used for media, instruments, dressings, IV equipment,
syringes, ets.
• Time and temperature can change due to size
• Steam must contact item’s surface
Figure 7.2 An autoclave.
Exhaust valve
(removes steam
after sterilization)
Steam to
chamber
Safety
valve
Pressure gauge
Operating valve
(controls steam from
jacket to chamber)
Steam
Door
Steam
chamber
Air
Perforated shelf
Steam jacket
To waste line
Sediment
screen
Thermometer
Automatic ejector valve
Pressure regulator
(thermostatically controlled;
for steam supply
closes on contact with
pure steam when air is
Steam supply
exhausted)
Figure 7.3 Examples of sterilization indicators.
PASTEURIZATION
• Reduces spoilage organisms and pathogens in
some food and liquids without damaging taste of
product
• Equivalent treatments
•
•
•
•
63°C for 30 min
High-temperature short-time: 72°C for 15 sec
Ultra-high-temperature: 140°C for <1 sec
Thermoduric(heat resistant) organisms survive
DRY HEAT STERILIZATION
• Kills by oxidation
•
•
•
•
Dry heat
Flaming
Incineration
Hot-air sterilization
Equivalent Treatments
Hot-Air
Autoclave
170˚C, 2 hr
121˚C, 15 min
FILTRATION
• HEPA- removes
microbes >0.3 µm
• Membrane
filtration- removes
microbes >0.22 µm
PHYSICAL METHODS OF MICROBIAL
CONTROL
• Low temperature inhibits microbial growth
(bacteriostatic)
• Refrigeration
• Deep-freezing
• Lyophilization
• High pressure denatures proteins
• Desiccation prevents metabolism
• Osmotic pressure causes plasmolysis
RADIATION
• Ionizing radiation (X rays, gamma rays, electron
beams)
•
•
•
•
Damages DNA
Can go through barriers
Used by the food industry on meats, vegetables, and spices
Also used on dental and medical supplies
• Nonionizing radiation (UV)
• Damages DNA
• Has to be in direct contact
• Microwaves kill by heat; not especially antimicrobial
PRINCIPLES OF EFFECTIVE
DISINFECTION
• Concentration of disinfectant
• Time
• Substance the disinfectant is being used against:
• Organic matter
• pH
EVALUATING A DISINFECTANT
Use-Dilution Test
Disk Diffusion Method
• Metal rings dipped in
test bacteria are dried
• Dried cultures are
placed in disinfectant
for 10 min
at 20°C
• Rings are transferred to
culture media to
determine whether
bacteria survived
treatment
• Filter paper is soaked
with a chemical
• Placed on an agar
plate with an organism
on it
• Look for zones of
inhibition
Figure 7.6 Evaluation of disinfectants by the disk-diffusion method.
Zone of inhibition
Chlorine
O-phenylphenol
Hexachlorophene
Quat
Staphylococcus aureus
(gram-positive)
Chlorine
O-phenylphenol
Hexachlorophene
Quat
Escherichia coli
(gram-negative)
Chlorine
O-phenylphenol
Hexachlorophene
Quat
Pseudomonas aeruginosa
(gram-negative)
• If you wanted to disinfect a surface contaminated
by vomit and a surface contaminated by a sneeze,
why would your choice of disinfectant make a
difference? 7-7
PHENOL AND PHENOLICS
• Disrupt plasma membranes
• Lysol
• Bacteria
BISPHENOLS
• Hexachlorophene
• Disrupt plasma membranes
• Used in hospital soaps
• Staphyloccocci and Streptococci
• Triclosan
• Disrupt plasma membranes
• Found in soaps, toothpaste, cutting boards, plastic
kitchenware
• Bacteria and yeast
BIGUANIDES
• Chlorhexidine
• Disrupts plasma membranes
• Surgical hand scrubs and preoperative scrubs
• Bacteria
HALOGENS
• Iodine
• Alters protein synthesis and cell membranes
• Bacteria, endospores, fungi, viruses
• Chlorine
•
•
•
•
Prevents enzyme system from functioning
Bleach
Disinfects drinking water, swimming pools, and sewage
Bacteria and viruses
ALCOHOLS
• Ethanol, isopropanol
• Denature proteins, dissolve lipids
• Require water
• Bacteria and fungi
HEAVY METALS
• Silver, Mercury, and
Copper
• Denatures proteins
• Silver nitrate- may be
used to prevent
gonorrheal ophthalmia
neonatorum
• Silver sulfadiazine- used as
a topical cream on burns
• Copper sulfate- is an
algicide
SURFACE-ACTIVE AGENTS, OR
SURFACTANTS
Soap- mechanical removal of
Degerming
microbes
Acid-anionic detergentsdairy utensils and equipment;
bacteria
Sanitizing
Quaternary ammonium
compounds
(cationic detergents)fungicidal, amebicidal,
virucidal
Bactericidal, denature
proteins, disrupt plasma
membrane
CHEMICAL FOOD PRESERVATIVES
• Organic acids
• Inhibit metabolism
• Sorbic acid, benzoic acid, and calcium propionate
• Control molds and bacteria in foods and cosmetics
• Nitrite
• Prevents endospore germination
• Put in ham, bacon, hot dogs, sausage
• Antibiotics
• Nisin and natamycin prevent spoilage of cheese
ALDEHYDES
• Inactivate proteins by cross-linking
• Bactericidal, tuberculocidal, virucidal, sporicidal
• Used on hospital instruments, endoscopes, and
respiratory therapy equipment
• Glutaraldehyde, formaldehyde
GASEOUS STERILANTS
• Denature proteins
• Sporicidal
• Use: heat-sensitive material
• Ethylene oxide
PLASMA
• Free radicals destroy microbes
• Used for tubular instruments used for arthroscopic
and laparoscopic surgeries
SUPERCRITICAL FLUIDS
• CO2 with gaseous and liquid properties
• Use: medical implants(bones, tendons, ligaments)
PEROXYGENS
• Hydrogen Peroxide
• Use: contaminated surfaces
Figure 7.11 Decreasing order of resistance of microorganisms to chemical biocides.
Table 7.7 The Effectiveness of Chemical Antimicrobials against Endospores and Mycobacteria