Microbiology study guide for unit 2 test.
Microbiology study guide for unit 2 test. BIOL 2230
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This 27 page Study Guide was uploaded by Allison Collins on Thursday March 31, 2016. The Study Guide belongs to BIOL 2230 at Middle Tennessee State University taught by Anthony L Newsome in Fall 2015. Since its upload, it has received 57 views. For similar materials see Microbiology in Biology at Middle Tennessee State University.
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Date Created: 03/31/16
MICROBIOLOGY UNIT 2 TEST Highlight = important term Highlight = important concept Highlight = important person or specific organism I. Microbial growth control 4 factors affect microbial growth: temperature, pH, oxygen, water availability A. Antiseptics and disinfectants • Sterilization -‐ destruction or removal of all forms of microbial l ife, including spores and viruses o NOT synonymous with disinfecting • Disinfection -‐ the process of destroying vegetative pathogens but not necessarily spores or viruses • Antiseptic vs. disinfectant o Antiseptics are applied to living tissue to prevent infection o Disinfectants applied to inanimate objects, so are stronger B. Physical means • Based on: heat, low temperature, desiccation (dehydration), osmotic pressure, filtration, radiation • Microbial control doesn’t necessarily mean killing the bacteria 1. Moist heat a. Autoclaves (heat under pressure) o 121C for 15 min at 15lb of pressure; must have moisture present b. Boiling water o Kills most vegetative forms of bacteria and most viruses in 10 minutes o Spores and hepatitis can survive several minutes or more in these conditions o Doesn’t achieve sterilization c. Pasteurization – mild heating (72C) o Also doesn’t achieve sterilization 2. Dry heat • 170C (340F) for 2 hours • Moist heat is more effective – takes 10-‐15 min at a lower temperature 3. Gas • Ethylene oxide for 4-‐18 hours • Denatures protein • Ideal for sterilizing electronic equipment and other heat-‐sensitive materials 4. Radiation a. Ionizing radiation (irradiation) – use of high-‐penetrating gamma rays o Gamma rays have enough energy to disrupt molecules – damages DNA or other cellular structures – kills organism or makes it incapable of reproducing o Used for single use medical supplies, tissue -‐based products, food (i.e. astronaut food) o Kills probiotics too b. Non-‐ionizing radiation o Less penetrating – useful for sterilization of surfaces o Ex: microwaves, UV rays 2 C. Chemical means 1. Phenols • First used by Joseph Lister (Listerine) • Ex: Chlorhexidine (Hibiclens) • Phenolics – phenol derivatives o Damage cell membranes, denature proteins o Ex: hexachlorophene (phisohex), Lysol 2. Halogens a. Iodine o Combines with microbial proteins to disable their function o Used as a tincture of iodine – a tincture is an alcoholic extraction o Iodophore – combinations of iodine and organic molecules § Includes Betadine and Isodyne • Contain povidone, a surface active agent b. Chlorine o Used as sodium hypochlorite – AKA bleach – most commonly used halogen o Chlorine is used as a gas to control microbial growth in drinking water 3. Alcohols • Proof – measure of amount of ethanol – twice the percent of ABV (alcohol by volume); ex 100 proof = 50% alcohol • Most widely used kind is 70 percent ethyl alcohol (ethanol -‐ EtOH) • Isopropyl alcohol (rubbing alcohol) 3 o Useful in disinfecting skin before injections because it evaporates quickly and leaves no residue 4. Heavy metals a. Silver – used as silver nitrate to guard against infection a nd cauterize wounds b. Copper – used as copper sulfate to slow growth of algae, also is antifungal agent in paint c. Zinc – used as zinc chloride in mouthwash 5. Soaps and detergents • Emulsification agents – break down and suspend fat molecules in the oily film on a surface – easier to wash away oil, debris, and MO 6. Aldehydes a. Formaldehyde – used as formalin, a solution of formaldehyde gas o Used for embalming b. Glutaraldehyde – used as a liquid for cold sterilization of hospital equipment 7. Oxidizing agents • Kill MO by releasing large amounts of oxygen – alters microbial enzymes • Hydrogen peroxide (H2O2) – wounds, contact lenses • Benzoyl peroxide – treats acne by inhibiting anaerobic growth 8. Quaternary ammonic compounds • Cationic detergents • Break down cell membranes of MO • Ex: Cepacol (mouth wash), Virex128, D.O.C. 64 4 II. Nucleic acid principles A. Nucleic acids – long polymers of nucleotides 1. 2 information storing molecules – primary function § RNA – 80 to 200,000 nucleotide units long § DNA – several million nucleotide units long 2. Each nucleotide has: phosphate group, pentose sugar, nitrogenous base o In RNA – ribose sugar o In DNA – deoxyribose sugar 3. Why called deoxyribonucleic acid/2 -‐deoxyribonucleic acid? o The nitrogenous bases of nucleic acids belong to 2 chemical classes: § Pyrimidine – 1 ring • RNA: uracil and cytosine • DNA: thymine and cytosine § Purine: 2 fused rings • RNA and DNA: adenine, guanine o **only need to memorize names, not exact chemical structure** B. DNA details 1. Important concept: in order to convey info, you must have VARIABILITY o Ex: bar code, alphabet, binary code o Nitrogenous bases vary in nucleotides (A, C, U/T, G) 2. DNA is double stranded – strands are COMPLEMENTARY & ANTI-‐ PARALLEL 5 o Pairs: A-‐T, T-‐A, C-‐G, G-‐C o Nucleotides associated via nitrogenous bases o Nitrogenous bases are always at 1’ carbon o Remember – purines (adenine and guanine) only go with pyrimidines (thymine and cytosine) and vice versa 3. True of all pentose sugars in nucleotides o 1’ Carbon – top right of pentose sugar -‐ connected to nitrogenous base o 2’ Carbon – bottom right of pentose sugar -‐ H (OH in RNA) o 3’ Carbon – bottom left of pentose sugar -‐ shares O with the phosphate group o 4’ Carbon – forms straight line with 3’ and 5’ carbon, top left of pentose sugar o 5’ Carbon – connects to O of phosphate group, not part of the pentagon o 1’ à 5’ is clockwise C. DNA Replication 1. DNA synthesis • 1 chromosome à 2 chromosomes o Is SEMICONSERVATIVE – each chromosome contains 1 of the original DNA strands plus one newly synthesized complementary strand 2. Replication fork • DNA unzips – forms a replication fork (handout) o As bases join the “unzipped” strands, eventually 4 strands total are involved (i.e. 2 DNA strands) o Nitrogenous bases are floating loosely and join complementary base on strands 6 o Moves forward due to action of DNA polymerase (enzyme) o DNA grows only in the 5’ à 3’ direction § Nucleotides only added to the 3’ end 3. 2 new strands o Continuous strand: fast and efficient o Discontinuous strand: not as efficient § Has to wait for fork to open because bases can only be added to 3’ end and is opposite of leading strand § This creates discontinuous fragments that are later joined together by DNA ligase • Discontinuous fragments of lagging strand – called Okazaki fragments § DNA polymerase – other major enzyme involved • Joins the nitrogenous bases • Antibiotics inhibit these enzymes in bacteria 4. Eukaryotic vs. Prokaryotic a. Prokaryotic o DNA gyrase – only in bacteria o Bacterial DNA is supercoiled – gyrase uncoils it o Antibiotics selectively inhibit it o Circular DNA (single circular chromosome) o Only 2 replication forks (vs. multiple in DNA) b. Eukaryotic cell – large chromosomes allow for multiple replication forks 7 III. Flow of genetic info 1. DNA (replicates itself) à transcription à RNA (m, t, r) à translation à protein (AA sequence) à start over 2. AA sequence in protein has direct relationship to nitrogenous bases in DNA A. Transcription (RNA synthesis) 1. Transcription – synthesis of a complementary strand of RNA from a DNA template 2. RNA is synthesized in the 5’ à 3’ direction o Only add nucleotides to the 3’ end (same as DNA) o At any particular point, only ONE strand is transcribed § This strand is called the “sense strand” § Other strand is the “nonsense strand” § Transcription will not occur in same spot on opposite DNA strand 3. The RNA transcript from DNA is complementary o DNA to RNA o A à U o T à A o C à G o G à C 4. Transcription generates 3 types of RNA o Messenger RNA (mRNA) § Bears message for protein synthesis o Transfer RNA (tRNA) § Carries AA to site of protein synthesis 8 o Ribosomal RNA (rRNA) § Are components of ribosomes 5. Gene – DNA segment that codes for polypeptides via mRNA, tRNA, and rRNA o Genes occur on chromosomes o Same in prokaryotes and eukaryotes 6. Transcription in bacteria • Occurs in cytoplasm alongside translation o Eukaryotic cells: DNA synthesis in nucleus, protein synthesis in cytoplasm • RNA polymerase binds to specific promoter region on DNA – called the Pribnow box – consists of TATAAT sequence of nucleotides • RNA arises from post-‐transcription modification o After RNA is synthesized, certain segments are removed before it becomes functional o Removed segments: introns o Exons: regions coding for RNA that end up in the final RNA product – i.e. regions of DNA that are transcribed o 90% of our DNA is contained in introns B. Translation Translation: process in which the genetic message carried by mRNA directs the synthesis of polypeptide chains with the aid of ribosomes 1. Summary: The copy strand (mRNA) leaves the chromosome à mRNA finds a ribosome à mRNA sticks to a ribosome à tRNA carries codons that connect with corresponding nucleotides on mRNA à tRNA also carries an amino acid à tRNA breaks off, leaving the amino acid à tRNA picks up another amino acid and waits for another complementary 9 codon à process repeats and each additional amino acid adds to an amino acid chain o So tRNA’s reaction with mRNA: tRNA delivers amino acids to corresponding nucleotides on mRNA o tRNA attaches to ribosome, which moves along the mRNA 2. Each set of 3 nucleotide bases of mRNA forms a codon o A codon codes for a single amino acid (most of the time) o Multiple codons can code for the same amino acid o Anticodon – associated with tRNA – 3 complementary bases to codon § tRNA has anticodon on one end and an amino acid on the other 3. Each time the tRNA attaches to the mRNA it leaves behind an amino acid, and eventually forms a polypeptide chain o Polypeptide chain gives rise to a functional protein o When done making protein, mRNA has a stop codon that indicates completion of translation à mRNA dissociates with ribosome § Stop codon does not code for any amino acid § There must be at least one tRNA for each amino acid 4. There are 64 total codons o 61 sense codons – that is, they specify incorporation of an amino acid into a protein § Some different triplet codons specify the same amino acid – is redundant o 3 nonsense (stop) codons – signal for ribosome to dissociate from the mRNA § Stop codons: UGA, UAG, UAA 10 • So: codons = mRNA , anticodons = tRNA o mRNA and tRNA pair only in the presence of a ribosome • Remember: protein synthesis takes place on the ribosome and mRNA acts as a blueprint C. Organization of the genetic code 1. The DNA sequence has a direct relationship to the amino acid sequence • There are 20 amino acids in proteins • Only nitrogenous bases are variable o Only 4 bases à need 20 codes (codons) 3 o 3 bases per codon à 4 = 64 combinations o Some codons code for the same protein o Ex: GCT, GCC, GGA, GCG all code for the amino acid Alanine IV. Mutations Mutation: change in DNA base sequence Mutagens: anything that can cause a mutation A. Point mutation – base substitution • At one point in DNA, one base is substituted for another • May or may not be an important change • After substitution, the polypeptide chain folds back on itself in formation of the protein • Depending on place of substitution, mutation may affect function of protein o Ex: active site may be altered, may inadvertently generate a stop codon (thus halting protein production) • The mutation is passed on to later proteins 11 B. Frameshift mutation • More problematic – end result is a totally inappropriate protein – always a bad consequence • One or more nucleotide base pairs is inserted or deleted from DNA à changes whole reading frame of mRNA à incorrect amino acid inserted into polypeptide chain à produces wrong protein • Genetic diseases often result of just one faulty protein – there are hundreds of types of proteins • Radiation can knock out nucleotides • Example of frameshift mutation operation: o Original sequence: ATA CCG CAG TTC o Deletion of first adenine: TAC CGC AGT TC_ C. Testing for mutation 1. Base analog: chemical similar to nitrogenous bases that get inadvertently incorporated into DNA o Cause faulty base pairing o Can be used as antiviral and antitumor drugs – very important in treatment of disease o Example: 2-‐aminopurine is very similar in chemical composition to adenine and can pair with cytosine à this causes incorrect RNA and thus incorrect protein o Base analogs can cause mutation o One ring or two ring structures are more likely to be incorporated into DNA and cause a mutation o Scientists are currently testing whether new chemicals will substitute into DNA as base analogs § Identify chemical in a product or drug and wait 20-‐30 years to observe effects 12 2. All chemicals are subject to the Ames test o Take particular bacteria and add a chemical o Humans and bacteria have the same nitrogenous bases o Bacteria divide every 20-‐30 minutes – quickly end up with millions of bacteria o Check bacteria for mutations § If so, significant chance it will affect human DNA o Uses strain of Salmonella or E. coli to test chemicals for their mutagenicity and thus their potential carcinogenicity D. Physical mutagens 1. UV light à Causes formation of thymine dimers o Dimer – bonding of two thymine molecules so that a pair is read as only one unit 2. Mutations can occur spontaneously o Generally spontaneous mutation rate is low – 1 per 10 9 replicated base pairs o Average gene is 103 base pairs long o Humans have about 23k – 25k genes o So average mutation rate is one per 10 replicated genes (1 per million) o Vast majority of mutations are harmful in eukaryotic organisms – often carcinogenic IV. Genetic transfer and recombination in bacteria A. Transformation o Naked pieces of DNA transferred from one bacterium to another o Single circular chromosome – when bacteria die, DNA pieces float around in environment – can be taken up by other bacteria 13 B. Conjugation o Transfer of plasmids (small extra-‐chromosomal pieces of DNA) C. Transduction o Bacteriophage – virus that only affects/infects bacteria o Attaches to bacteria and injects DNA to produce new bacteriophages • All 3 occur naturally V. Biotechnology Definition: use of living organisms to make useful objects; technological application that uses biological systems, living organisms, or their derivatives to make or modify products A. Genetic engineering – deliberate modification of organism’s genetic information by directly changing its nucleotide sequence in order to make new and different proteins • Original genetic engineering: selective breeding – used throughout human history • Variety of methods – collectively referred to as recombinant DNA technology 1. If you have a genetic disease, most times you are deficient in a protein o Solution: a. Put genes (DNA) into bacteria, o b. Let them produce the desired product, o c. Give desired product to deficient individual 2. Dangers of genetic engineering o Often easy to do o Put harmful toxin coding genes into common bacteria and release into environment – often these genes are impossible to get rid of 14 o Chemical warfare 3. Difficulty of using eukaryotic cells in genetic engineering o DNA must cross a large area to get to nucleus and cross membrane o Maybe infect a few cells and get transcription/translation, but what is their growth rate? § If not much growth at all, not enough to help/be of value o Human growth rate § Heart, kidneys, liver, nerve cells – very low in all – can’t multiply at all o Growth rate of average human tissue < bacteria o Exception: bone marrow à contains stem cells (undifferentiated cells) 4. Stem cells: have potential to develop into many different cell types in early growth o 4 types of stem cells: embryonic, cord blood (best option), adult, adipose (fat) tissue o Blocked fallopian tubes – test hormones before harvesting eggs and again before implantation – use stem cells from embryo o Leukemia – disease of blood where cell does not differentiate at proper ratios o Genetic defect – requires bone marrow transplant B. Examples of biotechnology 1. Insulin – hormone produced by the pancreas o Historically, medical insulin comes from a pig’s pancreas § Disadvantages from using pigs • Need a lot of pigs 15 • Can work – but not human insulin; is a foreign protein o Amino acid sequence is different • Some people became allergic o Can’t grow pancreas cells in lab o People can’t donate pancreas as a source of insulin o Late 1970s – more diabetics living longer, not enough pigs, DNA transcription was more understood o Thought: can we use bacteria to produce proteins that humans lack? o Insulin (made by humans) vs. humilin (made by E. coli) – recombinant DNA (rDNA) origin § Lantus also has rDNA origin 2. HGH – human growth hormone o In humans, produced by pituitary gland o From E. coli o Only legal use is for treatment of disease, e.g. dwarfism § Unforseen repercussions – abuse by athletes o A lot of cancer cells are activated by growth hormones o Causes unnaturally high level of testosterone 3. Hormone replacement therapy o Ultimate treatment would be gene therapy – inserting the correct DNA sequence into deficient individuals o Using bacteria to create proteins – a hormone is just a protein, which can be traced back to the DNA sequence § Ex: deficient growth hormone to treat diseases C. Restriction endonucleases 16 • Definition: recognize and cleave specific nucleotide sequences, usually 4-‐ 6 base pairs long o This protective mechanism exists to protect from viruses o The difference in the nucleotide base sequence is what makes us all different • 1980s – started realizing how biotechnology can help humans o If you add restriction endonucleases to humans, it will cut human DNA into pieces o Because no two humans have same DNA sequence, it will cut them all into differently sized pieces for different DNA o Useful in forensics • RFLP (restriction fragment length polymorphism) o Segment of DNA when treated with restriction endonucleases that generates DNA fragments whose size differentiates from one person to another o Used in forensics, genetic studies o RFLP databases – convicted felons are put in automatically – now a national database is used for cold hits § Cold hits – no reason for association, direct RFLP matches made D. Genetic probe 1. Probe: a DNA or RNA molecule which is used to locate a complementary RNA or DNA by hybridizing (through complementary base pairing) with it o Can be made to identify a bacterium or a genetic disease Genetic ID card – 23 & Me o Genetic sequences exist that are associated with any physical condition 17 o Vary in levels of directness of relationship with condition o Genetic ID card Indicates the increased risk of diseases, not definite occurrence o Drop DNA strand onto silicon chip and test for attachment to genetic probe o Ethical questions § Do insurance companies have the right to know your test results? § Results on a developing fetus could affect parents’ decision to follow through with pregnancy or more testing § Can also associate sequences with mental issues such as bipolar disorder, schizophrenia, depression, personality traits § Does an employer have the right to know? § Employers have been found to secretly test blood samples in some cases § Horse racing – “speed gene” test Babies – triple screen test o High percentage of false positive results o Genetic counselors can help analyze results o FISH – fluorescent in situ hybridization § Amniocentesis – extract amniotic fluid – risky procedure § Double check triple screen for accuracy o High probability that you’ll be genetically probed at some point in your lifetime 2. Hybrid – double stranded nucleic acid in which strands differ in origin 3. ATCG sequence distinguishes between bacteria (and eukaryotes) 18 o Manufacture complementary sequence (as a guess) and if it binds to extracted DNA on a slide, the particular ATCG sequence is present 4.Indicator molecule (color) – color change on slide indicates that DNA sequence stuck to slide, so its complementary strand is present 5. DNA synthesis or oligonucleotides synthesis (in a lab) o About 2-‐30 bases long o 2 purposes § Probes à DNA hybridization à identify genes or bacteria § Primers à PCR à manufacture copies of a segment of DNA o In situ hybridization – using genetic probe (oligonucleotides), indicator molecule In vitro – in a test tube o Cheaper than using agar plate; common process E. Polymerase Chain Reaction • Relatively simple process • Kary Mullins developed it and won Nobel Prize in 1993 • Jurassic Park novel based on PCR 1. PCR definition: an in vitro (in a test tube) reaction in which a specific region of DNA is amplified many times by repeated synthesis of DNA using DNA polymerase and specific primers to define the ends o f the amplified region o Application: make large quantities of a particular DNA sequence o Primer – a piece of DNA that provides an end to which DNA polymerase can add nucleotides – approx. nucleotides long in this process 2. Fundamental steps 19 1. Synthesize fragments with sequences (primers) identical to those on either side of the targeted sequence (approx. 20 nucleotides) 2. Denature DNA by heating it to 94C for 15 seconds o Separate 2 DNA strands 3. Add multiple primers and lower temperature to 68C for 60 seconds to allow primers to anneal (hydrogen bond) to DNA o Because the primers are added in excess, the the targeted DNA strands will almost always anneal to the primers rather than to each other 4. Add nucleotide triphosphates and DNA polymerase 5. The DNA polymerase extends the primers and synthesizes copies of target DNA sequence o 2 strands à 4 strands 6. Repeat heating and cooling cycle and each cycle generates a complementary strand from each preexisting strand o 20 cycles will produce about 1 million copies o Pieces ranging in size from <100 base pairs to several thousand base pairs in length can be amplified • Use a heat stable polymerase from a thermophilic bacteria – only polymerases are able to function at the high temps used in the PCR o Taq polymerase -‐ from Thermus aquaticus, bacteria from hot springs o Vent polymerase – from Thermococcus litoralis, bacteria from deep sea vents 3. Forensics application: rape case in Chattanooga o Semen from rape victims was used to generate RFLP from DNA o Cigarette butt from rape suspect used to extract small amount of DNA and amplify with PCR 20 o DNA from semen matched with DNA from cigarette butt, suspect convicted o Has since been deemed unlawful to confiscate DNA in such a manner unless suspect is a convicted felon F. Recombinant DNA technology (rDNA) 1. Ex: Hepatitis vaccine – originally very expensive, today is free o Original method: extract and kill virus from blood sample from someone who is Hepatitis positive o Now: take nucleic acid from virus, introduce to bacteria, bacteria produces proteins à use protein for vaccine 2. rDNA technology in bacteria based on: a. Restriction endonucleases o found in bacteria – cut DNA (not found in humans) b. DNA ligases (join ends of DNA) c. Plasmids d. Gram negative bacteria 3. E. coli is most commonly used bacteria in biotechnology (most strands are nonpathenogenic) • Easy to grow • Dirt cheap to grow • Grows quickly • We know its genetics well – easy to place genes into it that are responsible for protein production 4. Bacterial production of proteins used for vaccines • Take cells producing desired product (eukaryotic or prokaryotic) o Isolate DNA and treat with restriction endonucleases o Some of the DNA fragments have desired genes 21 • Take bacteria resistant to ampicillin (antibiotic) and resistance carried on plasmids o Isolate plasmids and break open with restriction enzymes • Mix DNA fragments from cells with desired product + broken plasmids from abx-‐resistant bacteria • Add DNA ligase to join ends together o Now you have plasmids with antibiotic genes and foreign DNA • Screen bacteria for production of desired protein and product o Add bacteria (E. coli) sensistive to ampicillin (i.e. don’t have plasmids) to agar plate containing ampicillin § Often plasmids don’t get into bacteria – check for presence on an agar plate § Only E. coli with plasmids (recombinants) will grow § Test each colony on the agar plate for proteins § One colony with the protein means success – can now duplicate bacteria from that colony VI. Antibiotics A. Definition: a metabolite produced by one microorganism that inhibits the metabolic pathway of another microorganism 1. Certain bacteria are more sensitive to certain bacteria – identify bacteria when possible 2. Don’t use antibiotics to prevent wound infections o Exception: post-‐surgical wounds 3. 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 22 o The vast majority of antibiotics are produced by other organisms B. 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 C. Problem when pathogen is a eukaryotic cell/MO: o Example: fungus, yeast, protozoan, worm (helminth) o 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 o Don’t have their own metabolic pathways – use enzymes from our cells D. Desirable criteria for antibiotics 1. Selective toxicity 2. Don’t produce hypersensitivity o Ex: many people are allergic to Penicillin 3. MO not easily resistant 4. Soluble in body fluids and not rapidly broken down or excreted E. 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) – commonly used to break down bacterial cell walls 23 o 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 § β lactamase – AKA penicillinases – enzyme that breaks open the beta lactam ring § 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 a. Streptomycin – attach and change shape of bacteria’s ribosomes – mRNA is then read incorrectly o Bacteria produce non-‐functional protein b. Tetracyclines – inhibit attachment of tRNA to mRNA o Amino acid chain not constructed 3. Injury to plasma membrane a. Amphotericin B – antifungal – very toxic, users must be hospitalized b. Polymyxin B – OTC – topical use only c. 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 24 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 F. Bacteria in nature and agriculture 1. Ocean bacteria – untapped source of vast number of organisms – constant search for new antibiotics 2. Who use the most antibiotics? Farmers o Poultry, seafood, etc. o Promotes antibiotic resistance o Aureomycin – sold at co-‐op for cheap – very effective – fed to animals G. Treatments • Antibiotic susceptibility resistance o All healthcare systems follow the same protocol o Kirby-‐Bauer test § Determine if bacteria are sensitive to a particular antibiotic § Isolate bacteria and look for zone of inhibition H. 2 types of antibiotics 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 25 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 VII. Combinations of drugs A. 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) B. Antagonistic effect: effect of 2 drugs taken simultaneously is less than the sum of each drug’s individual effects o Ex: penicillin + tetracycline (inhibition of protein synthesis) C. 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 D. Principle of treatment: give a large initial dose of antibiotic E. Principle of use 1. Some bacteria are resistant before antibiotic use begins 26 o This occurs through genetic variation – likely to happen 2. Give large amount to quickly reduce number of bacteria to manageable levels so that our bodies can q uickly clear before resistant forms emerge o If unable to clear resistant forms, they start to multiply and you get sick again – same bacteria but different variety o At this point you need to try a different antibiotic 3. 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 27
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