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Medical Microbiology > Chapter 7: The Control of Microbial Growth > Flashcards

Chapter 7: The Control of Microbial Growth Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

Sterilization

A

Desruction or removal of all forms of microbial life, including endospores but with the possible exception of prions

Usually done by steam under pressure or sterilizing gas, such as ethylene oxide

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2
Q

Commercial Sterilization

A

Sufficient heat treatment to kill endospores of Clostridium botulinum in canned food

More-resistant endospores of thermophilic bacteria may survive, but they will not germinate and grow under normal storage conditions

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3
Q

Disinfections

A

Destruction of vegetative pathogens

May make use of physical or chemical methods

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4
Q

Antisepsis

A

Destruction of vegetative pathogens on living tissue

Treatment is almost always by chemical antimicrobials

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5
Q

Degerming

A

Removal of microbes from a limited area, such as the skin around an injection site

Mostly a mechanical removal by an alcohol-soaked swab

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6
Q

Sanitation

A

Treatment intended to lower microbial counts on eating and drinking utensils to safe public health levels

May be done with high temperature washing or dipping into a chemical disinfectant

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7
Q

Germicide

A

Rapidly kills M/O, but not necessarily endospores

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8
Q

Fungicide

A

Kills fungi

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9
Q

Virucide

A

“Kills” or inactivate viruses

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10
Q

Bacteriostasis

A

“Stasis” = Halt

Ihibits bacterial growth and multiplication

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11
Q

Sepsis

A

Greek word for decay/putrid.

Indicator of bacterial contamination

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12
Q

Asepsis

A

The absence of pathogens from an object or area

Critical in surgical procedures!

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13
Q

Microbial Death Rate

A

Populations of m/o subjected to a treatment die a constant rate

This “death rate” can be plotted as a straight line

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14
Q

Conditions Influencing Microbial Death

A

Types and numbers of microbes

Temperature

Physiological state of the m/o

Environment

Time of exposure

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15
Q

Where Do Antimicrobial Agents Work?

A

The plasma membrane:
Cell membrane permeability may be
affected by altering lipid and protein
content -> “Leaky” membranes

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16
Q

Where Do Antimicrobial Agents Work?

A 
Nucleic acids (DNA and RNA) and proteins:
Some antimicrobials break bonds that hold 
these molecules together, others 
interfere with synthesis
17
Q

Physical Methods of Microbial Control?

A 
Heat (moist vs. dry)
Filtration
Temperature
Dessication
Osmotic Pressure
Radiation (ionizing vs. non-ionizing)
18
Q

Physical Methods of Microbial Control - Heat

A

A. Dry heat: Incineration, hot air sterilizationrequires 170°C for 2 hours

B. Moist heat: Boiling (10 min) kills most m/o; but spores and viruses may survive

Autoclaving = Steam under pressure, moisture must touch every surface to sterilize
15 psi, 121°C, 15 min

C. Pasteurization: Mild heating that is sufficient to kill spoilage or disease organisms without damaging the taste of the product (72°C, 15s)
HTST vs. UHT

19
Q

Physical Methods of Microbial Control - Filtration

A

Used for heat-sensitive liquids passed
through a membrane filter with pores too small for
m/o to pass through (0.22μm, 0.45μm)

HEPA (High efficiency particulate air) filters = 0.33μm

20
Q

Physical Methods of Microbial Control - Low Temperatures (depends on the bacteria) At refrigerator temperatures (4°C))

A

Metabolic rates of most m/o are reduced
Bacteriostatic

Most m/o are dormant in the freezer (-20°C)

21
Q

Physical Methods of Microbial Control - Dessication (removal of water)

A

Water is required for growth; dried foods won’t support m/o growth

But, restoring water restores growth
Lyophilization (freeze drying) involves fast
freezing (-70°C) and removal of water in a vacuum

22
Q

Physical Methods of Microbial Control - Osmotic Pressure (high salt or sugar concentration)

A

Hypertonic environment
Generally, molds and yeasts resist osmotic pressure
better than bacteria

23
Q

Physical Methods of Microbial Control - Radiation

A

A. Ionizing radiation: X-rays, gamma rays
Short wavelength
“Unzip” the strands of DNA
Used to sterilize pharmaceuticals, disposables, and mail…
B. Non-ionizing radiation: UV light
Less energy, less penetrating than ionizing
Causes DNA damage (mutagenesis), thymine dimers
“Germicidal” lamps
C. Microwaves kill indirectly by heating food, but…

24
Q

The Problem

A

No single disinfectant is an “all purpose” agent.

It is essential to find the proper agent/purpose!

25
Q

Phenol (carbolic acid)

A

Used by Lister in the 1860s for aseptic surgery

Seldom used today…smelly and irritating!

Injures plasma membranes and inactivates enzymes

Found in some cough drops (anesthetic effect) and Chloraseptic

26
Q

Phenolics: derivatives of phenol

A

Not as irritating as phenol

Used in combination with detergents

Injures plasma membranes and inactivate enzymes

Stable in the presence of organic compounds

Notable phenolics:
phenylphenol (Lysol): Effective surface disinfectant
Triclosan: Found in “antibacterial” soaps and toothpaste
Widespread resistance has been documented in several
species of bacteria

27
Q

Halogens

A

A. Iodine
One of the oldest and most effective antiseptics!
Inhibits protein function and FX cell membranes
Found as “tincture” (Dissolved in alcohol)
Also found as an “iodophor”, a combination of
iodine and an organic molecule
Less irritating and won’t stain (Betadine)
B. Chlorine
All chlorines form hypochlorous acid in water
which enters cells and inhibits enzyme function

Used as a gas (Water supplies, swimming pools, and sewage treatment)

Sodium hypochlorite (aka Bleach or Clorox) in a 
10% solution is an excellent disinfectant

Chloramines (chlorine + ammonia) are more stable
than most chlorines; used in water treatment to
control taste and odor problems

28
Q

Alcohols

A

Bacteriocidal and fungicidal, not effective against spores or non-enveloped viruses

Not used as an antiseptic for wounds (ouch!)

Denature proteins, inactivate enzymes, and
disrupt plasma membranes

Ethanol and isopropanol (rubbing alcohol) are
widely used at concentrations of 60-95%

70% ethanol in water is optimum for antiseptic
and disinfectant activity

29
Q

Heavy Metals

A

Can be germicidal or act as an antiseptic

Denature proteins

Oligodynamic effect allows small amounts of
metals (coins) to inhibit microbial growth

1% silver nitrate solution is used to prevent
gonorrheal eye infections in newborns

Silver sulfadiazine-impregnated dressings

Copper sulfate is used to destroy algae in pools,
reservoirs, and fish tanks

Zinc chloride is used in mouthwashes, and zinc
oxide is used in paints as an antifungal

30
Q

Surface-active agents

A

Decrease surface tension of liquids
Charged sanitizers react with the plasma membranes
and inactivate enzymes

31
Q

Chemical food preservatives…organic acids and derivatives

A

Inhibit enzymatic or metabolic activity
Used as preservatives to control mold growth in
foods and cosmetics
Sorbic acid (cheese); benzoic acid (soft
drinks); calcium propionate (bread); and
sodium nitrate (meats)
Methylparaben and propylparaben inhibit mold
growth in liquid cosmetics and shampoos

32
Q

Aldehydes

A

Very effective antimicrobials; inactive protiens

33
Q

Gaseous chemosterilizers

A

Chemicals that sterilize in a chamber
Ethylene oxide is commonly used and kills all microbes and spores by inactivating proteins
Used for disposable medical supplies and delicate
equipment
Propylene oxide and beta-propiolactone are also important
Disadvantage of chemosterilizers gases are carcinogenic, often require lengthy exposure

34
Q

Oxidizing agents (Peroxygens)

A

Oxidize cellular components (Ozone)
Hydrogen peroxide (H2O2) is a good disinfectant
for fomites; not a good antiseptic for superficial wounds; but good for deep wounds
Catalase converts H2O2 -> ???
Benzoyl peroxide is used for acne
Peracetic acid is sporicidal
Used in food processing (no residues) and for
disinfecting medical supplies (endoscopes)

35
Q

MIC - minimum inhibitory concentration

A

The lowest concentration of a disinfectant or chemotherapeutic agent that prevents bacterial growth

36
Q

MBC - Minimum bacteriocidal concentration

A

The lowest concentration of a disinfectant or chemotherapeutic agent that kills the test organism

37
Q

Gluteraldehyde

A

Among the most effective chemical control agent because it is considered a relatively safe sterilizing agent

Medical Microbiology (2 decks)

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