BIOL 2230 3/29 and 3/31 notes
BIOL 2230 3/29 and 3/31 notes BIOL 2230
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This 7 page Class Notes was uploaded by Allison Collins on Thursday March 31, 2016. The Class Notes belongs to BIOL 2230 at Middle Tennessee State University taught by Anthony L Newsome in Fall 2015. Since its upload, it has received 24 views. For similar materials see Microbiology in Biology at Middle Tennessee State University.
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Date Created: 03/31/16
3/29 Antibiotic: a metabolite produced by one microorganism that inhibits the metabolic pathway of another microorganism • Certain bacteria are more sensitive to certain bacteria – identify bacteria when possible • Don’t use antibiotics to prevent wound infections o Exception: post-‐surgical wounds • About half of antibiotics from the genus Streptomyces o Common genus because they produce chemicals that inhibit other microorganisms’ processes o Other common MO’s – Bacillus, Penicillium o The vast majority of antibiotics are produced by other organisms Spectrum of activity – action of antibiotics • INHIBIT: • 1. cell wall formation • 2. protein synthesis • 3. DNA synthesis • 4. metabolic pathways o The newest antibiotics also function in these ways Problem when pathogen is a eukaryotic cell/MO: • Example: fungus, yeast, protozoan, worm (helminth) • Share many of the same metabolic pathways that our cells do, thus making these MO’s difficult to selectively inhibit Viral infections are also difficult to treat • Don’t have their own metabolic pathways – use enzymes from our cells Desirable criteria for antibiotics • 1. Selective toxicity • 2. Don’t produce hypersensitivity • Ex: many people are allergic to Penicillin • 3. MO not easily resistant • 4. Soluble in body fluids and not rapidly broken down or excreted Action of antimicrobial drugs 1. Inhibition of cell wall synthesis • Most effective against Gram positive bacteria o Interfere with synthesis of peptidoglycan • A) Penicillin(s) – have β lactam ring – central to structure of molecule o Many bacteria that are resistant to Penicillin are able to break down the beta lactam ring o β lactamase – AKA penicillinases – enzyme that breaks open the beta lactam ring o Penicillin then can’t work to inhibit cell wall function • B) Cephalosporins (another type of antibiotic) – also inhibits cell wall synthesis 2. Inhibit protein synthesis • Streptomycin – attach and change shape of bacteria’s ribosomes – mRNA is then read incorrectly o Bacteria produce non-‐functional protein • Tetracyclines – inhibit attachment of tRNA to mRNA o Amino acid chain not constructed 3. Injury to plasma membrane • Amphotericin B – antifungal – very toxic, users must be hospitalized 2 • Polymyxin B – OTC – topical use only • Polypeptide antibiotics o Hot area of research for new/better antibiotics o Found when studying salamander limb regeneration – noticed that when limbs were cut off, salamanders never got skin infections o Removed skin, ground, and added to bacterial cultures – inhibited bacterial growth o Salamanders, frogs, goldfish, etc produce magainins – new class of antibiotics o Old Russian tradition: keeping a frog in a bucket of milk will keep it from spoiling 4. Inhibit nucleic acid synthesis • Inhibit unwinding of DNA o Ex: Nalidaxic acid blocks DNA gyrase (unwinds bacterial DNA so that it can replicate) • Inhibit DNA polymerase 5. Inhibit metabolism/enzyme activity • Sulfanilamide: sulfa drug o Prevents folic acid synthesis – necessary vitamin for bacteria Ocean bacteria – untapped source of vast number of organisms – constant search for new antibiotics Who use the most antibiotics? Farmers • Poultry, seafood, etc. • Promotes antibiotic resistance • Aureomycin – sold at co-‐op for cheap – very effective – fed to animals Treatments 3 • Antibiotic susceptibility resistance • All healthcare systems follow the same protocol • Kirby-‐Bauer test o Determine if bacteria are sensitive to a particular antibiotic o Isolate bacteria and look for zone of inhibition 3/31 Combinations of drugs • Synergism – effect of 2 drugs taken simultaneously is greater than the sum of each drug’s individual effects o Ex: penicillin (inhibition of cell wall synthesis) + streptomycin (inhibition of protein synthesis • Antagonistic effect: effect of 2 drugs taken simultaneously is less than the sum of each drug’s individual effects Resistance • 1. Bacteria produce enzymes that destroy antibiotics o Ex: beta lactamace (penicillinase) • 2. Inhibit entry of antibiotic into cell so it can’t inhibit protein synthesis, DNA synthesis, etc. o Ex: thick capsule on a bacterium Principle of treatment: give a large initial dose of antibiotic Principle of use • Some bacteria are resistant before antibiotic use begins • This occurs through genetic variation – likely to happen • Give large amount to quickly reduce number of bacteria to manageable levels so that our bodies can quickly clear before resistant forms emerge 4 • If unable to clear resistant forms, they start to multiply and you get sick again – same bacteria but different variety • At this point you need to try a different antibiotic • A well-‐functioning immune system is essential to fighting bacterial infections o Compromised immune systems include very young, very old, organ transplant patients (take immunosuppressant), cancer, HIV/AIDS Antibiotics – 2 types • 1. Broad spectrum o Kills both gram negative and gram positive bacteria o Use when you aren’t sure which bacteria you’re dealing with o Also kills normal flora, which kill pathogens naturally § Ex: human mouth and urogenital tract are lined with bacteria and some yeast (Candida albicans) § Broad spectrum abx kills normal flora à yeast able to multiply § Candidasis à systemic candidiasis • Massive amount of Candida albicans in intestines, which causes a yeast allergy • 2. Narrow spectrum o Kills only gram positive OR gram negative bacteria *******end of test 2 material******** 5 UNIT 3 Few of the many species of bacteria cause disease <1% of bacteria from nature can be cultured Virulence – severity of disease caused by MO • The more virulent, the more severe Attenuated – MO has lost ability to cause disease • Ex: rubella and mumps vaccines – contain live viruses Etiology – study of the cause of a disease • Etiologic agent – MO that causes specific disease or condition Toxins • Endotoxin – LPS (lipopolysaccharide) – only in gram negative bacteria • Exotoxin – released into environment o Ex: tetanus • Enterotoxin – acts on intestines o Not as common as other types Classification of bacteria • Binomial nomenclature – genus + species o Developed by Carolus Linnaeus • Bergey’s Manual – major sourcebook of all classified bacteria – now available online • Classification based on: • 1. Morphological features – shape/appearance • 2. Differential staining o Gram, acid fast, etc. • 3. Biochemical tests 6 • 4. Serology – how bacteria react to antibodies o ^^traditional classification More recently: • 5. Protein analysis • 6. Base composition of nucleic acids Normal flora • Humans are germ free at birth • Soon acquire flora within hours/days • Lactobacillus – acquired when passing through birth canal • Also soon acquire E. coli Areas of body with normal flora • Skin • 2 predominant bacteria: Staphylococcus aureus & Staphylococcus epidermidis • Skin is a salty/hypertonic environment • MRSA – major human pathogen – 20% of us are carriers 7
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