1、Antibiotics Hugh B.Fackrell Filename:antibiot.pptOutline History Ideal properties Sources“Sulfas”Antimetabolites antibiotic synergism Major Groups of antibiotics Mechanisms of actionHistory Salvarsan 606 Prontosil PenicillinSalvarsan 606 Paul Ehrlich early 1900s syphilis arsenic+organic compound Ani
2、line dyes-wasnt able to find the magic bullet”Prontosil 1930s,Gerhard Domagk Prontosil 1935,Jacques and Therese Trefoncel discovered that the active compound in Prontosil was Sulfanilamide sulfanilamide“Sulfas”Penicillin 1928,Alexander Fleming antibacterial activity in Penicillium mold (called it Pe
3、nicillin)1938,Howard Florey and Ernst Chain developed Penicillin as an effective antibioticAntimicrobial Therapy Antimicrobics substances produced by microbes that inhibit other microbes Semi-synthetic antibiotics naturally produced but altered Synthetic antibiotics:derived from chemicalsIdeal Prope
4、rties of an Antibiotic Low toxicity for patient kills the invading microorganism without damaging the host no adverse side reactions non allergenic High toxicity for microbe bactericidal not bacteriostatic broad spectrum Low risk of other infectionsMore Characteristics drug can be administered orall
5、y or parenterally(by injection)Soluble in tissue fluids absorbed by and dissolved in tissues or body fluids levels of active drug sustained long enough to kill the invading agent Long“Shelf”lifeStill More Characteristics Low probability of resistance Microbial drug resistance develops slowly microbi
6、cidal rather than microbistatic Not inactivated by organic material Assists the host in eliminating the infecting microbe Not a powerful allergenSources of AntibioticsMost spore-forming microorganisms Fungi Penicillium penicillin,Cephalosporium griseofulvin Bacteria Bacillus bacitracin,polymyxin,tyr
7、othricin,colimycin,gramicidin Streptomycetes Aminoglycosides,nystatin,chloramphenicol,erythromycin,tetracylcine.Mechanisms of Drug Action inhibit cell wall synthesis inhibit nucleic acid synthesis inhibit protein synthesis interfere with cell membrane functionSulfa DrugsSulfa vs PABAStructure of Sul
8、fa DrugsFolic Acid MetabolismFolic Acid InhibitionAntibiotic SynergismAntibiotic Synergism Sulfonamide+trimethoprim Effective dosage 10%of two separately Broader spectrum of action Reduce emergence of resistant strainsMajor Groups of AntibioticsMajor Groups of Antibiotics Aminoglycosides streptomyci
9、n,kanamycin,neomycin,gentamicin,spectinomycin,tobramycin,amikacin Beta lactams Penicillins,cephalosporins Lincomycins lincomycin clindamycinMajor Groups of Antibiotics Macrolides erythromycin,carbomycin Polypeptides polymyxin,colimycin,bacitracin,tyrothricin Polyenes amphotericin B,nystatin Rifamyci
10、ns RifampinMajor Groups of Antibiotics Synthetic pyridine isoniazid,ethambutol sulfonamides sulfanilamide,sulphisoxazole misc nitrofurans,metronidazole,nalidixic acid Tetracyclines oxytetracline,chlortetracycline Unclassified Chloramphenicol,vancomycinPENEMS Carbapenems“Ideal”antibiotics non toxic b
11、road spectrum good“Shelf”life effective at very low conc Attach to Penicillin Binding Proteins found in cell membrane Gm+ve lysis through loss of cell wall integrity Gm-ve filamentous bacteria loss of septum formationAdverse Effects of Antibiotics Aminoglycosides Ototoxic-destroys cochlear hair cell
12、s renal toxic Chloramphenicol depresses bone marrow aplastic anemia fatal“Grey baby”syndrome Penicillins allergy anaphylaxis Vancomycin thrombophlebitis ototoxic renal toxic Polymyxin,bacitracin colimycin renal toxic Sulfas skin allergy anemia renal toxic hepato toxicAdverse Effects of Antibiotics B
13、road spectrum Super infections Candida albicans Clostridium difficle Staphylococcus Gram-veMode of Action of AntibioticsMode of Action of Antibiotics Inhibit Synthesis of Cell Wall Damage Cell Membrane Inhibit Protein Synthesis Inhibit Nucleic acid SynthesisBacterial Cell Wall Peptidoglycan many lay
14、ers in gram positives thin in gram negative protects the cell against rupture from hypotonic environmentsSynthesis of peptidoglycan(1/4)Uridine diphosphate(UDP)derivatives of NAM and NAG are synthesized in the cytoplasm Amino acids are sequentially added to UDP-NAM to form the pentapeptide chain usi
15、ng ATP as an energy source.The two terminal D-alanines are added as a dipeptide(Cycloserine)Synthesis of peptidoglycan(2/4)The NAM-pentapeptide is transferred from UDP to a bactoprenol PO4 at the membrane surface.Bactoprenol is a 55-Carbon alcohol that attaches to NAM by a pyrophosphate group and mo
16、ves peptidoglycan components through the hydrophobic membrane UDP-NAG adds NAG to the NAM-pentapeptide to form the peptidoglycan repeat unitSynthesis of peptidoglycan(3/4)The completed NAM-NAG peptidoglycan repeat unit is transported across the membrane to its outer surface by the bactoprenol pyroph
17、osphate carrier The peptidoglycan unit is attached to the growing end.Synthesis of peptidoglycan(4/4)The bactoprenol carrier returns to the inside of the membrane to collect another NAM-pentapeptide.Bactoprenol pyrophosphate must give up phosphate to connect Bacitracin Finally,transpeptidization-int
18、erbridges formedInhibit Synthesis of Cell Wall penicillin,bacitracin,vancomycin,cephalosporin,carbapenems Inhibition of Cell Wall Synthesis Cycloserine-inhibits peptidoglycan sub-unit formation Vancomycin-inhibits peptidoglycan elongation Beta-lactam antibiotics-Penicillins lactam antibiotics block
19、peptidases required to connect inter bridges Cephalosporins bind to the peptidases that are essential to cross link the glycan molecules.Murray 2.4&5.4,p.10Inhibition of cell wall synthesis Cycloserine-inhibits the addition of the two terminal D-alanines Bacitracin-inhibits the transport of the subu
20、nits to their position in the cell wall Vancomycin-inhibits the elongation of the peptidoglycan to form connecting unitsInhibition of Cell Wall SynthesisNatural PenicillinsSemi Synthetic PenicillinsSemi Sythetic Penicillins-2Structure of PenicillinHydrolysis of Beta Lactam RingComparison of Structur
21、esPen G in BloodDamage Cell Membranelpolymyxin,colimycin,nystatin,amphoteracin,tyrothricin Injury of Plasma MembranePolymyxinMembraneCytoplasmPolymyxin action Polymyxin B binds to the cell membrane to disrupts its structural and permeability propertiesInhibit Protein Synthesis Binds to 50S ribosomal
22、 subunit prevents peptide chain elongation clindamycin,chlorampenicol,erythromycin block rRNA(23S)lincomycin,macrolides Binds to 30S ribosomal subunit misreading of mRNA aminoglycosides-genetamcin Blocks binding of tRNA-AA to 30S tetraclyclinesInhibition of TranslationTranslationInhibition of Peptid
23、e BondInhibition of Ribosome MovementInhibition of tRNA AttachmentMisreading mRNAInhibit Nucleic acid SynthesislQuinolones Ciprofloxacin and other quinolones Inhibits DNA gyrase Blocks DNA replication Inhibits mitochondrial DNA conc in tissues too low for toxicity Urinary and intestinal infectionsIn
24、hibition of DNA ReplicationInhibit Nucleic Acid Synthesis Rifamycin Inhibits DNA dependent RNA polymerase Blocks transcription DNA-RNAAcylovir vs DeoxyguanosineInhibition of TranscriptionAntimetabolites Sulfonamides Donald D.Woods Sulfanilamide blocks folic acid folic acid is essential to the synthe
25、sis of DNA and RNA Para amino benzoic acid(PABA)not incorporated into folic acid Reversible inhibition High PABA competitively inhibit sulfanilamide Inhibited metabolites,SynthesisDrug Resistance synthesis of enzymes that inactivate the drug decrease in cell permeability and uptake of the drug chang
26、e in the number or affinity of drug receptor sites modification of an essential metabolic pathwayDevelopment of Drug Resistance intrinsic chromosomal mutations-low probability acquired transfer of extra chromosomal DNA from a resistant species to a sensitive one Plasmids TransposonsPlasmids resistan
27、ce factors or R factors transfered by conjugation,transformation or transductionTransposons sequences that can move from plasmid chromosome plasmid plasmidClinical Trials patient-has a diagnosed infection-two possibilities:a)the new drug is the drug of choice by testing b)the patient has not respond
28、ed to other drugs and the new drug is testing well in the lab samples of blood etc.taken to determine all the possible parameters:level of antimicrobial and presence of agent cultures of infecting agent taken 2 times per day disappearance of the bacteria and patient recovery conclude a successful tr
29、ialReference:lab manual p.270Minimum Inhibitory Concentration 1.test for antimicrobial activity 2.dilute antibiotic(pictures of tubes)3.range selected obtained from therapeutic index 4.add to medium 5.add pure culture of isolated bacteria 6.incubate-tubes that are clear after 16 hours incubation at
30、35 C are subcultured 0.1 ml removed and plated on suitably rich medium-usually the agar version of the liquid growth mediumReference:lab manual p.270Kirby-Bauer Plate Sensitivity disks impregnated with various concentrations of appropriate antibiotics are placed aseptically on innoculated plates mea
31、surement of drug concentrations in the blood preclinical trials subjects receive varying dose levels and intervals of dosage pretrials usually determine the route of entry-oral or parenteral(injected subcutaneously,intramuscularly,etc.)pretrials determine the carrier substanceSubjects Tested for Ant
32、imicrobial Levels blood,lymph,urine,feces tested for effective levels depending on disease also of concern is rapid metabolism(catabolism)of the drug and also rapid excretionDisk Diffusion Tests diffusion of antibiotic from disk controlled by agar concentration Zone of Inhibition controlled by diffusion rate level of sensitivity each antibiotic is unique
