9 BIO 326R control of microbes

9 BIO 326R control of microbes - BIO 326R Controlling...

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BIO 326R Controlling bacteria
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Proteins as targets Most any organism can be killed if its proteins cease to function properly Preventing protein function can be specific or general Specific: e.g. penicillin inhibits transpeptidase. It has little/no effect on other proteins General: Alcohol denatures a large number of proteins about equally well. This includes host proteins, so they will kill human cells as well (or better) than bacterial cells. You can cure someone’s bacterial infection with penicillin. 70% ethanol can be used for topical or surface infections but not for internal infections. Many of the treatments or chemicals we talk about today will work as denaturants – i.e. they nonspecifically denature proteins and/or membranes.
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Membranes as targets General specificity problems – phospholipids are phospholipids, membranes are membranes (low therapeutic ratio) Often restricted to topical use Polymixins – cyclic peptide with a long hydrophobic tail Cyclic peptide is large and bulky and binds the saccaride portion of LPS well. The hydrophobic portion inserts into the outer membrane. From there it can move and associate with the cytoplasmic membrane. For these reason polymyxins are much more effective versus gram negative than gram positive. Neurotoxic and nephrotoxic, absorbed poorly through GI tract. Channel forming ionophores and true ionophores (e.g. DNP) Detergents General disruption of membranes and denaturation of proteins, usually through disrupting hydrophobic interior.
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Antiseptics/Disinfectants Alcohol At 70%, acts as a protein denaturant Usually for surface, instrument sterilization Silver / colloidal silver Binds proteins in cell membranes, interferes with respiration Silver nitrate (freq. used for eye infections) and colloidal version (wounds/bedsores) Not a miracle cure, but not toxic even at high levels. Triclosan Frequently found in commercially available antibacterial toothpastes, mouthwashes and soaps Inhibits fatty acid synthesis Mercury compounds Mercurochrome etc - banned in USA now One resistance mechanism is from changing organic form of Hg to elemental form – some environmental benefits? “elemental” Mercury (Hg) is toxic and dangerous. Methylmercury (CH3Hg) is extremely toxic. Some bacteria have enzymes which convert methylmercury to elemental mercury.
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Antiseptics/Disinfectants Iodine Binds to histidine, tyrosine, tryptophan (all have ring structures), non-specific protein denaturant Tincture of iodine: iodine salts in alcohol Highly effective – viruses, fungi, spores Hydrogen peroxide Release of oxygen, creation of radicals, effervescent action aids in debridement Debridement : removal of debris, particularly of fomites Fomites : inanimate objects which may harbor or carry infectious agents Benzalkonium chloride Quaternary ammonium (NR4) Surfactant/detergent - Used as hand scrub, facial wash. Note that removing bacteria is just as good
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9 BIO 326R control of microbes - BIO 326R Controlling...

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