Lecture DetailsEdit

Priscilla Johanesen; Week 9 MED1011; Microbiology

Lecture ContentEdit

Cleaning is done prior to any sterilisation/disinfection. Sterilisation kills or removes all viable organisms, physical and chemical. Disinfection removes or kills most viable organisms, physical or chemical. Antisepsis removes microbes from skin. Risk factors for microbial transmission can be equipment that penetrates skin or mucous membranes, equipment that requires specialised decontamination, equipment that can contact skin but not penetrate, and human hands.

Heat can be moist or dry, radiation can be gamma or UV, filtration or chemicals can sterilise or disinfect. Moist heat is much more efficient and effective, causes inactivation of proteins, aids penetration of heat into materials. Boiling does not kill all organisms. Moist heat and pressure kills bacterial cells and viruses as well as endospores. Increasing pressure increases the temperature at which water boils. Autoclave does this.

Dry heat kills by inactivation of cell components by oxidation, hot air kills slower than moist heat. Incineration destroys microbes.

UV is not terribly penetrating but is good for disinfecting surfaces and air, achieved by long term exposure to UV light, used in disinfection of instruments, surfaces and water in hospitals, is damaging to human tissue. Ionising radiation produces free radicals that break down DNA, is for heat sensitive materials and some food.

Filtration physically removes microorganisms from heat sensitive liquids or gases, membrane filter composed of polymers with different pore sizes.

Traditional chemicals for sterilisation are ethylene oxide gas, glutaraldehyde and formaldehyde; inactivate proteins and nucleic acid bases to kill a broad spectrum of microorganisms, toxic, flammable and irritant. Recently chemicals are vapour phase hydrogen peroxide, peracetic acid, chlorine dioxide and ozone. Chlorine is for decontamination for blood spills.

Antiseptic is used to kill harmful microorganisms without damaging the tissue. Sanitisation is thorough cleaning of an object or utensil to remove most microoorganisms. Asepsis is prevention of microbes of getting to a patient. Nocosomial is breakdown in sterilisation/disinfection procedures. An antimicrobial is any substance used to treat infection, antibiotic is low MW compounds that inhibit or kill growth of bacteria.

Peptidoglycan synthesis is a polymer of N-acetyl glucosamine (NAG) and muramic acid (NAM). NAM subunits are joined by peptide cross links. Cross linking is catalysed by carboxypeptidases and transpeptidases. Penicillin binds PBPs.

Beta lactams modify target site (PBP), prevention of access to target site (porins), production of beta lactamases cause hydrolysis of antibiotics, activity inhibited by clavulanic acid.


Mims Chapter 36

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