Lecture 18, 10/24 (Maybruck 3); Control of Microbial Growth

Audio for today's lecture is available here.

• • Slide 1 (handout from 10/22)
• Alcohols characterized as a hydrocarbon group linked to one or more hydroxel groups
• Alcohol has hydrophobic an hydrophilic end. The hydrophilic end is the reactive end - it actively bonds to other molecules.
• Surfactants enter into phospholipids bylayer of a cell membrane. This screws up selectively permeable layer of the cell membrane preventing the cell from functioning properly.
• Alcohol has the surfactant ability at 50% or greater concentration of alcohol.
• Also involved with the denaturing of proteins. If there is low water present then the alcohol will be less effective.
• Viruses with cell envelope are susceptible to alcohol
• • Slide 2
• Oxygen radicals – their metabolism requires oxygen to form energy. The oxygen used sometimes transforms into these oxygen radicals. Highly reactive compounds – create chemical bonds with whatever they can . . . RNA, protein, DNA
• Hydrogen peroxide is an example of oxygen radical
• At 3% can be an effective antiseptic
• At 35% - sterilant
• Oxygen radicals in general are good as a chemical decontaminant for anaerobic organisms.
• • Slide 3
• Surfactants (similar to detergents) – hydrophilic end has an overall positive charge. This is effective as most of our cells have an overall negative charge. This allows the bonding of the surfactant to the cell membrane.
• Soaps - mechanical removal of debris
• • Slide 4
• Main effect of heavy metals is the denaturing of proteins (causes them to unfold) if that metal is not typically associated with that protein.
• Heavy metal compounds
• Mercury, silver, gold, copper, arsenic, zinc
• Cofactor – metal ion that helps enzyme function
• Intermediate activity level
• Anaerobic organisms are susceptible to hydrogen peroxide
• • Slide 5 (he skipped a few)
• Aldehydes –
• Molecules that contain CHO group
• Two types: glutaraldehyde and formaldehyde
• Sugars are characteristic of an aldehyde
• Glutaraldehyde
• Cross link proteins – makes it more toxic. Binds quickly to surface proteins and such. It will also make its way into the cell itself. This messes up function of protein.
• Effective way to kill EVERYTHING. Kills vegetative cells in a few minutes and formaldehyde in a few hours.
• Effective preservitive because it does not lyce the cells. This allows the structure of the organism to be preserved.
• Formaldehyde
• Binds to proteins and nucleic acids
• Effective preservative because it does not lyce the cells. This allows the structure of the organism to be preserved.
• • Slide 1 (handout 10/24/07) Antimicrobial Chemotherapy – using drugs to destroy or remove microorganisms
• What is the perfect drug? (FYI: none exist, so we comprimise)
• Easily administered
• Upon administration it goes straight to the problem spot
• Easily excreted from the body
• Selectively toxic – goes after the bad stuff and not the good stuff
• • Slide 2
• Chemotherapy
• Prophylaxis – drug used to prevent the infection from occurring. (administered to office workers during anthrax scares)
• Antibiotics – chemicals released from microorganisms and fungi. They destroy and kill other microorganisms and fungi.
• Narrow spectrum antibiotic – specific in its target. Narrow range of microorganisms that it can eliminate.
• Broad spectrum antimicrobial – destroys wider range of cells
• • Slide 3
• Primary goal of antimicrobial chemotherapy – creating a drug effective in its removal of microorganisms.
• Microbocidal effect – kill unwanted microorganism
• Selectively toxic
• How is this goal achieved
• Make list of characteristics that allows it (pathogen) to survive
• make list of characteristics that allows our cells to survive
• compare theses two lists and determine the difference.
• Various things that you can target
• inhibit cell wall synthesis
• inhibit nucleic acid synthesis and structure
• inhibit protein syntheses
• alter cell membrane structure
• inhibit folic acid synthesis
• • slide 4: antimicrobial target: cell wall
• cell walls (peptidoglycan) protect cell from osmotic shock. The cell would lyce if it were not protected.
• subslide (drugs that target cell wall synthesis)
• cycloserine – inhibits formation of basic subunits of peptidoglycan.
• vancomycin – prevents elongation of peptidoglycan
• penicillin and cephalosporins – target the peptide bond between glycan sugars. Prevent cross linking of glycan molecules
• those drugs that target the cell wall are narrow in spectrum. This is because the cell wall they are attacking is found in gram (+) bacteria.
• In order for these things to work the organism has to be vegetative. A vegetative organism is always adding to the peptidoglycan layer, if it is not producing peptidoglycan then the drugs are useless (they also have no effect on endospores)
• • slide 5 targeting nucleic acids
• In the context of bacterial microorganisms this is a broad spectrum approach.
• Replication – DNA synthesis
• transcription – formation of RNA
• antibiotic Rifampin – blocks transcription. Binds to RNA polymerase and prevents the RNA polymerase from transcribing.
• Hydroxyurea – prevents formation of nucleotides (found in DNA and RNA: guanine, cytosine, thymine, adenine). It does this by binding to Ribonucleotide reductase.
• • Slide 6
• Mitomycin blocks DNA synthesis → cross linking guanines preventing DNA
• ATGGTCAG
• TACCAGTC