These lecture notes will provide an outline of information from the lectures. They are not complete. They should be used to help follow the lecture and as a guideline for information I think is important. You will need to fill in the gaps.


Chapters 21 and 22

 These notes were updated February 17, 2001, and are ready for printing by Spring 2001 Med Micro. students.

I.    Physical Control of Microbes

A.    Using Heat 1.    Direct Flame (dry heat) a)    Effectively sterilizes in seconds through incineration
b)    Drawbacks: only heat-resistant/disposable objects 2.    Hot-Air Oven (dry heat) a)    Effectively sterilizes through radiating dry heat, IF correct amount of time is applied
b)    Oxidizes microbial proteins
c)    160oC for two hours destroys bacterial endospores
d)    Time may vary according to the material containing the endospores
e)    Useful for dry powders, water-free oil substances, glassware
f)    Drawbacks: organic matter insulates (so sanitize first)
g)    If correct amount of time is not used, sterilization fails 3.    Boiling Water (moist heat) a)    Not considered an effective sterilizing agent because bacterial endospore destruction is not assured
b)    Also, inactivation of all viruses is not assured
c)    HOWEVER, it WILL kill most microbes within ten minutes of boiling
d)    Fungal spores, protozoal cysts, large numbers of hepatitis A virus require more time (30 minutes or more)
e)    Bacterial spores require two hours or more
f)    Drawbacks: organic matter insulates (so sanitize first) 4.    Autoclave (moist heat) a)    This is moist heat in the form of pressurized steam
b)    Most dependable method of sterilization
c)    Pressure of 15 pounds/square inch is applied (1)   Steam's temperature consequently rises to 121.5oC
(2)    15 minutes will sterilize d)    Quality control measures should be utilized (endospore incubation after autoclaving)
e)    Drawbacks: heat labile material cannot be sterilized 5.    Fractional Sterilization a)    AKA tyndallization
b)    100oC for 30 minutes, followed by incubation, 3 times, over three days 6.    Pasteurization a)    NOT sterilization
b)    Used on liquids
c)    Goal was to destroy Mycobacterium tuberculosis (once considered the most heat-resistant bacterium, although Coxiella burnetii is more heat resistant) (1)    62.9oC for 30 minutes (holding method)
(2)   71.6oC for 15 seconds (flash pasteurization)
(3)   82oC for 3 seconds (ultrapasteurization) 7.    Hot Oil a)    Used by dentists and some physicians
b)    Hot oil at 160oC for one hour is used to sterilize instruments B.    Using Methods Other Than Heat 1.    Filtration a)    Mechanical device for removing microbes from a solution
b)    Inorganic filters use porcelain/ground glass (Seitz filter)
c)    Organic filters use diatomaceous earth
d)    Membrane filters use organic compounds such as cellulose acetate/polycarbonate
e)    HEPA filters filter air 2.    Ultraviolet Light a)    Radiant energy having a wavelength between 100 and 400 nm
b)    265 nm is most destructive to bacteria
c)    Causes adjacent thymine molecules in DNA to link together (thymine dimers) (1)   Thus, proteins cannot be transcribed 3.    Radiation other than UV Light a)    X rays and Gamma Rays (1)   Ionizing radiation
(2)   Gram positive bacteria are more sensitive to ionizing radiation than Gram negative bacteria 4.    Microwave a)    Has longer wavelength than UV light
b)    Does not sterilize 5.    Laser beam a)    Sterilizes in fraction of a second IF beam reaches all parts of the material
b)    Is concentrated light energy 6.    Ultrasonic Vibrations a)    High-frequency sound waves
b)    In fluids, cause the formation of microscopic bubbles (cavities) (1)   Cold boiling results c)    Cavities collapse, sending out shock waves (1)   Called cavitation d)    Useful for breaking open tissue cells
e)    Cavitrons are used by dentists to clean teeth
f)    May achieve sterilization if used with an effective germicide
g)    Usually used as a cleaning agent followed by autoclaving C.    Preservation Methods are Bacteriostatic 1.    Drying
2.    Salting causes water to move out of microbe (dehydrates)
3.    Low temperatures lower metabolic rates of microbes II.   Chemical Control of Microbes A.    Evaluation of Antiseptics and Disinfectants 1.    Phenol coefficient (PC)
2.    In-use test B.    Halogens (The "salt-formers") 1.    Chlorine a)    Effective against broad variety of organisms (1)   Most Gram positive AND Gram negative bacteria
(2)   Many viruses, fungi, and protozoa b)    NOT sporicidal
c)    May be added as a gas or as part of an organic/inorganic compound (1)   Sodium hypochlorite (NaOCl) and calcium hypochlorite [Ca(OCl)2]
(2)   MUST BE ADDED TO WATER for optimal disinfection
(3)   Hypochlorite compounds release free chlorine IN SOLUTION
(4)   NaOCl is commercial bleach, which contains about 5 percent hypochlorite
(5)   To disinfect clear water: ½ teaspoon household chlorine bleach per 2 gallons water, with 30 minutes contact time d)    Chloramines are organic chlorine compounds used for root canal therapy and general wound antisepsis 2.    Iodine a)    More reactive
b)    More germicidal
c)    Found widely in nature
d)    Tincture of iodine (1)   2 percent iodine and sodium iodide dissolve in ethyl alcohol
(2)   To disinfect clear water: add 5 drops tincture of iodine per quart of water, with 30 minutes contact time
(3)   Antiseptic for wounds e)    Iodophor (1)   Iodine-detergent complexes
(2)   Wescodyne, Ioprep, Iosan, Betadine 3.    Phenol and Phenolic Compounds a)    Phenol is standard against which other antiseptics/disinfectants are evaluated in phenol coefficient test
b)    Active against Gram positive bacteria
c)    Activity is reduced in presence of organic matter
d)    Caustic to skin
e)    Phenol derivatives are cresols (1)   Greater germicidal activity
(2)   Lower toxicity f)    Bisphenols are combinations of two phenol molecules (1)   Lysol is an example
(2)   Hexachlorphene is another example
(3)   pHisoHex contained hexachlorophene and a pH balanced detergent cream that was used extensively in pediatric nurseries (a)   Use was stopped because of associated neurological damage (4)   Chlorhexidine is a surgical scrub and effective against plaque and gingivitis
(5)   Trichlosan is a broad-spectrum antimicrobial agent used in antibacterial soaps, lotions, toys, underwear, kitchen sponges, etc. 4.    Heavy metals a)    Very reactive with proteins, especially sulfhydryl groups (-SH)
b)    Mercury used as mercuric chloride (1)   Toxic
(2)   Antimicrobial activity is reduced if other organic matter is present
(3)   Mercurochrome, Merthiolate, Metaphen contain mercury combined with carrier molecules c)    Copper
d)    Silver (1)   Silver nitrate used in eyes of newborns to protect against Neisseria gonorrhoeae 5.    Alcohols a)    Preferred alcohol is ethyl alcohol (1)   Effective against vegetative bacterial cells, including tubercle bacillus
(2)   No effect on spores
(3)   Denatures proteins and dissolves lipids
(4)   Strong dehydrating agent
(5)   Organic matter must be removed first
(6)   50-70 percent alcohol solution is recommended because water prevents rapid evaporation and assists penetration into tissues b)    Isopropyl alcohol (rubbing alcohol) (1)   High bactericidal activity 6.    Formaldehyde a)    Formalin is formaldehyde plus water (1)   Formalin is used to inactivate viruses and to produce toxoids, both when making vaccines 7.    Ethylene oxide a)    Useful for sterilizing heat-sensitive materials
b)    Has excellent penetration and sporicidal ability
c)    Toxic and explosive 8.    Glutaraldehyde a)    Destroys vegetative cells within 10-30 minutes; spores in ten hours
b)    Organic matter must be removed 9.    Hydrogen peroxide
10.   Soap a)    Wetting agents: emulsify and solubilize particles 11.   Detergents a)    Strong wetting agents
b)    Encourage leakage from cytoplasm by altering cell membrane
c)    Can be anionic or cationic (1)   Catonic detergents are the quats (quaternary ammonium compounds)
(2)   Bacteriostatic, especially with Gram positive bacteria 12.   Dyes a)    Used for staining, media, and antispesis
b)    Gentian violet used for trench mouth and thrush infections 13.   Acids a)    Used as antiseptics/disinfectants
b)    Useful against tinea infections III.   Halting the Spread of Infection A.    Standard Precautions
B.    Transmission-based Precautions a)    Airborne
b)    Droplet
c)    Contact

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