Sterilization involves the destruction or removal of ALL living microbes spores and viruses on an object or in an area Sanitation reducing the numbers of pathogens to a level considered safe Microbiostatic static remain in place reduce microbial numbers or inhibit their growth Microbiology Chapter 7 Outline 7 1 STILL GO OVER CLASS NOTES Microbicidal cide kill Kills microbes Bactericidal Fungicidal Bacteriostatic Fungistatic Know terminology in notes 7 2 Factors effecting antimicrobial treatments Number of microbes in the population Microbial characteristics Environmental influences Time of exposure Killing with heat is fast reliable and relatively inexpensive The effectiveness of heat for sterilization is a function of time and temp Mycobacterium tuberculosis are destroyed in 30 minutes at 58 degrees Celsius but in only 2 minutes at 65 degrees Celsius and in a few seconds at 72 degrees Celsius Each microbial species has a thermal death time and each species has a thermal death point Moist Heat Kills microorganisms by denaturation Boiling water o Penetrates materials much more rapidly than dry heat because water molecules conduct heat better than air o Moist heat can be used at a lower temp and shorter exposure time than for dry heat Denaturation change in the chemical or physical property of a protein o Boiling water is not considered a sterilizing agent because the destruction of bacterial spores and the inactivation of viruses cannot always be assured o If boiling water must be used to destroy microorganisms then the materials must be thoroughly cleaned to remove traces of organic matter o Minimum exposure period should be 30 minutes except at high altitudes Autoclave moist heat in the form of pressurized steam is regarded as the most dependable methods for sterilization INCLUDING THE DESCRUCTION OF ENDOSPORES Kills microorganisms by denaturation o Sterilizing agent is the heat not the pressure o Reduces sterilizing time o Contain a sterilizing chamber into which articles are placed As steam flows into the sterilizing chamber a special valve increases the pressure to 15 pounds square inch and the temp rises to 121 5C o Takes about 15 minutes Pasteurization reduces the bacterial population in liquids such as milk and destroys organisms that may cause spoilage and human disease Kills microorganisms by denaturation Not sterile still some bacteria left See class notes Dry Heat Filtration The form in which dry heat is used to sterilize depends on the nature of the substance to be treated Incineration using a direct flame to burn microbes to ashes very rapidly Example Hospital disposables Example the flame of the Bunsen burner in lab is employed for a few seconds to sterilize the bacteriological loop before removing a sample from a culture tube Hot air sterilization The hot air oven uses radiating dry heat for sterilization Very effective method of sterilization but requires temp of 170C 340F for 2 hours SEE FIGURE 7 5 IN BOOK PAGE 201 A mechanical method used to remove microorganisms suspended in liquids or gases The most common is the membrane filter which consists of a pad of nitrocellulose acetate or polycarbonate mounted in a holding device As fluid passes through the filter organisms are trapped on the membrane because they are too large to pass through the pores Bacterial cells trapped on the filter multiply and form colonies when the filter pad is placed on an agar culture plate High efficiency particulate air HEPA filter consists of a mat of randomly arranged fibers that trap particles microorganisms and spores Prevent 99 of all particles including microbes and spores with a diameter larger than 3 micro meters from escaping as aerosols into the lab air See notes UV LIGHT Wavelength b w 100 and 400 nm When microbes are subjected to UV light cellular DNA absorbs the energy and adjacent thymine molecules link together kinking the double helix and disrupting DNA replication and transcription UV light effectively reduces the microbial population where direct exposure takes place Used to limit airborne or surface contamination in a hospital room morgue pharmacy toilet facility or food surface operation X rays and Gamma Rays o Have wavelengths shorter than UV light o As they pass through microbial molecules they force electrons out of their shells creating ions Radiations are called ionizing radiations Desiccation Drying SEE NOTES Osmotic Pressure Salting Loss of water from cells See notes Cold Refrigeration Lowers metabolic rate Many psychotrophs remain alive even at 0C SEE NOTES TABLE 7 1 ON PAGE 209 SUMS EVRRRRYTHANG UP Chemical Methods of Microbial Control Disinfectant the chemical agent used to eliminate or reduce pathogens EXCEPT ENDOSPORES Antiseptic if the object treated is living such as human skin tissue the chemical used is called an antiseptic These two things are usually microbicidal Asepsis means free of disease causing microbes Degerm mechanically remove organisms from its surface Phenol Coefficient PC number indicating the disinfecting ability of an antiseptic or disinfectant in comparison to phenol Halogens Oxidize Proteins Chlorine and Iodine represent intermediate level chemical agents Halogens are oxidizing agents or protein synthesis inhibitors that combine with and inactivate certain cytoplasmic proteins such as enzymes Killing almost always occurs within 30 minutes after application Chlorine Iodine Bisphenols Effective against a broad variety of organisms High concentrations can be sporicidal Available as a gas and as organic or inorganic compounds Widely used in municipal water supplies and swimming pools Slightly larger than chlorine and more reactive and germicidal Phenol and Phenolic Compounds Phenol carbolic acid is a low level to intermediate level chemical agents First used by Joseph Lister Remains the standard against which other antiseptics and disinfectants are evaluated using the phenol coefficient test Act by denaturing proteins especially in a cell membrane Has a pungent odor and is caustic to the skin therefore its seldom used Phenol derivatives phenolics have greater germicidal activity and lower toxicity than the parent compound Combinations of two phenol molecules Have become prominent in modern disinfection and antisepsis Chlorhexidine is a bisphenol relative that is used as a surgical hand scrub and a superficial skin wound cleanser Hexachlorophene achne lotions like pHiso Hex Trichlorophene ingredient in antibacterial soap mouthwash etc