Antibiotici

1. Antibiotici Sono prodotti microbici o loro derivati in grado di uccidere i microrganismi suscettibili o bloccarne l’espansione.

2. There are many chemicals that are lethal to bacteria — cyanide does a good job — but they cannot be used to cure infections because they are lethal to the host as well. The problem, then, is to find substances that attack a metabolic pathway found in the bacterium but not in the host. This is not an insurmountable problem for bacterial pathogens because prokaryotes differ in many respects from eukaryotes. Antibiotics

3. The fact that a microorganism is capable of destroying one of another species was not established until the latter half of the 19th cent. when Pasteur noted the antagonistic effect of other bacteria on the anthrax organism (therapeutic use). Antibiotics: History Paul Ehrlich developed the idea of selective toxicity: that certain chemicals that would be toxic to some organisms, e.g., infectious bacteria, would be harmless to other organisms, e.g., humans (1904, rosso tripan-tripanosoma-malattia del sonno) In 1928, Sir Alexander Fleming, a Scottish biologist, observed that Penicillium notatum, a common mold, had destroyed Staphylococcus bacteria in culture.

4. The photo shows how the growth of bacteria on the agar in a culture dish has been inhibited by the three circular colonies of the fungus Penicillium notatum. The antibiotic penicillin, diffusing outward from the colonies, is responsible for this effect. Penicillin is made from cultures of P. chrysogenum that has been specially adapted for high yields.

5. Penicillin was finally isolated in 1939 (Nobel nel 1945 a Fleming, Florey e Chain) in 1944 Selman Waksman and Albert Schatz, American microbiologists, isolated streptomycin and a number of other antibiotics from Streptomyces griseus. Antibiotici History

6. Possono essere a spettro ristretto o ad ampio spettro Prodotti da batteri e funghi Attinomiceti e Bacilli sono i batteri maggiori produttori Antibiotici

7. according to their action against the infecting organism: some antibiotics attack the cell wall; some disrupt the cell membrane; the majority inhibits the synthesis of nucleic acids and proteins, the polymers that make up the bacterial cell. on the basis of chemical structure, as penicillins, cephalosporins, aminoglycosides, tetracyclines, macrolides, sulfonamides, etc etc… Classification

11. Natural products. Semi-synthetic products. Completely synthetic products. Antibiotici

12. Completely synthetic products:Sulfa Drugs, sulfamidici o sulfonamidici Sulfanilamide was the first Sulfa Drug used asantibacterial agent. acido folico deriva dalla dieta acido folico • nucleic acid synthesis • protein synthesis • nucleic acid synthesis • protein synthesis nell’uomo nei batteri

13. Completely synthetic products:Sulfa Drugs • Sulfanilamide was the first Sulfa Drug used asantibacterial agent. Both bacteria and their human hosts require folic acid for nucleic acid synthesis (it is converted into purines and thymidine) as well as protein synthesis (precursor of the amino acids methionine and glycine). Bacteria synthesize their folic acid starting with para-aminobenzoic acid (PABA), while we must ingest our folic acid already formed (it is a vitamin). Sulfanilamide, and the other sulfa drugs, are analogs of PABA; they compete with PABA and, when chosen, block the synthesis of folic acid. Mammals ignore PABA and its analogs and thus can tolerate sulfa drugs.

15. These synthetic molecules block the final step in the conversion of PABA to folic acid so they, too, block nucleotide and protein synthesis in bacteria but not in mammals. Completely synthetic products: Folic Acid Analogs

16. The quinolones are a family of synthetic broad-spectrum antibacterial drugs. Quinolones exert their antibacterial effect by preventing bacterial DNA from unwinding and duplicating. Fluoroquinolones inhibit the topoisomerase II ligase domain. This modification, coupled with the constant action of the topoisomerase II in the bacterial cell, leads to DNA fragmentation via the nucleasic activity of the intact enzyme domains. Fluoroquinolones

17. Nalidixic acid is effective against both gram-positive and gram-negative bacteria. The Chink in the Armor = DNA topoisomerases The fluoroquinolones block the action of two bacterial topoisomerases — enzymes that relieve the coils that form in DNA when the helix is being opened in preparation for replication or transcription or repair The topoisomerases in eukaryotes are not affected

18. A number of natural products, penicillin for example, have been discovered that are antibiotics suitable for therapy. They were originally discovered as secretions of fungi or soil bacteria. Soils are complex ecosystems, and it is not surprising that its inhabitants have evolved chemical defenses against each other. Natural products.

19. These are natural products that have been chemically modified in the laboratory (and pharmaceutical facility) to improve the efficacy of the natural product reduce its side effects circumvent developing resistance by the targeted bacteria expand the range of bacteria that can be treated with it Semi-synthetic products.

20. La parete batterica nella sua componenete del peptidoglicano costituisce il bersaglio per molti antibiotici Tali antibiotici agiscono impedendo la sintesi del peptidoglicano Antibiotici diversi agiscono in momenti diversi del processo sintetico Sintesi del monomero (fosfomicina) Trasporto attraverso membrana (bacitracina) Formazione del pentapeptide (cicloserina) Assemblaggio finale  transpeptidizzazione (penicilline e glicopeptidi) ANTIBIOTICI DI PARETE

21. Blocco del primo step La fosfomicina, prodotta da S. griseus, blocca la sintesi del NAM, grazie alla inibizione di MurA

22. Blocco del primo step Non si forma il NAM-pentapeptide

23. Blocco del secondo step Bacitracina Cyclic polypeptides produced by Bacillus subtilis. These peptides disrupt both gram positive and gram negative bacteria by interfering with cell wall and peptidoglycan synthesis.

24. Blocco del terzo step The beta-lactams have a characteristic ring structure. The beta-lactams all work by interfering with the synthesis of the bacterial cell wall — a structure that is not found in eukaryotes.

25. penicillins such as • -penicillin G (a natural product) produced by the fungus P. chrysogenum • -ampicillin (a semi-synthetic) • cephalosporins Most are semi-synthetics derived from the secretion of the mold Cephalosporium.

26. During normal bacterial growth, bacterial enzymes called autolysins put breaks in the peptidoglycan in order to allow for insertion of peptidoglycan building blocks (monomers of NAG-NAM-peptide). These monomers are then attached to the growing end of the bacterial cell wall while transpeptidase enzymes join the peptide of one monomer with that of another in order to provide strength to the cell wall. Penicillins and cephalosporins bind to the transpeptidase enzyme (SUICIDE SUBSTRATE) and block the formation of the peptide cross-links. This results in a weak cell wall and osmotic lysis of the bacterium.

27. Animation Illustrating the Role of Penicillins in Blocking Transpeptidase Enzymes from Assembling the Peptide Cross-Links in Peptidoglycan

28. Vancomycin is a glycopeptide antibiotic obtained from Nocardia orientalis and is effective only for gram-positive bacteria . Vancomycin is bactericidal and appears to exert its effect by binding to the precursor units of bacterial cell walls, inhibiting their synthesis. This binding occurs at a different site of action from that of penicillin. The net result is an alteration of bacterial cell wall permeability. Glicopeptidi: la Vancomicina Vancomycins bind to the peptides of the monomers and block transpeptidase enzymes from forming the peptide cross-links.

29. Glicopeptidi Vancomicina Teicoplanina Dalbavancina Balimicina cloroeremomicina

30. Animation Illustrating the Role of Vancomycin in Blocking Transpeptidase Enzymes from Assembling the Peptide Cross-Links in Peptidoglycan

31. The 70S bacterial ribosome differs in several ways from the 80S eukaryotic ribosome. MACROLIDE AMINOGLICOSIDI

32. These are products of actinomycetes (soil bacteria) or semi-synthetic derivatives of the natural products. Examples are: streptomycin kanamycin neomycin Aminoglycosides • The aminoglycosides bind to the 30S subunit of the bacterial ribosome and • interfere with the formation of the initiation complex • cause misreading of the mRNA. Although the eukaryotic ribosome in the cytosol is relatively unaffected by these drugs, ribosomes in the mitochondria are 70S and sensitive to their effects.

33. These are natural products derived from soil actinomycetes or their semi-synthetic derivatives. Tetracyclines Tetracyclines bind to the 30S subunit of the bacterial ribosome. They prevent the transfer of activated amino acids to the ribosome so protein synthesis is halted.

34. Bind to the 23S rRNA molecule in the large (50S) subunit of the bacterial ribosome where they block the elongation of the growing peptide chain. Because of their similar action, the development of antibiotic resistance to one usually extends to all the others. Eritromicina Claritromicina Azitromicina Tilosina Macrolides struttura macrociclica a 14 termini L-cladinosio D-desosamina • products by actinomycetes (soil bacteria) or semi-synthetic derivatives.

35. Cloramfenicolo antibiotico prodotto da Streptomyces venezuelae, scoperto nel 1947. • si lega alla subunità 50S ribosomale bloccando il meccanismo di traduzione. • si interpone in uno spazio della subunità 50S tra il sito A e il sito P, bloccando l' enzima peptidil-transpeptidasi, che è adibito al trasporto della catena proteica dal sito A al sito P.

37. Antibiotici che agiscono sulle membrane Un poliene è una sostanza (un alchene) contenente diversi doppi legami in una struttura carboniosa a lunga catena. I farmaci polienici come l'amfotericina B o la nistatina contengono una catena carboniosa polienica ancorata ad una struttura polialcolica parallela. Questi composti, per la loro peculiare struttura, si legano al colesterolo (blanda adesione) e all'ergosterolo (adesione tenace), grazie alla formazione di legami ad alta affinità. Inoltre, gli antifungini polienici sono in grado di legarsi a vicenda, attratti l'un l'altro dalla presenza di gruppi ad affinità idrofilica ed idrofobica. Queste proprietà, comportano la formazione di canali di membrana aventi nell'anello interno i composti polienici e nell'anello esterno, l'ergosterolo o il colesterolo. La presenza dei canali altera l'equilibrio osmotico (perdita di potassio, sodio, zuccheri) della cellula fungina con compromissione delle funzioni cellulari e successiva lisi. A differenza degli altri farmaci che agiscono sulla parete cellulare (fungostatici, bloccano crescita e proliferazione), i composti polienici hanno una diretta attività fungicida, ovvero, in grado di uccidere i funghi infestanti. Tuttavia, benché l'amfotericina B sia un farmaco molto potente e con un ampio spettro d'azione, non è privo di attività tossica, spesso anche molto spiccata; la sua non perfetta selettività, comporta il legame anche con il colesterolo, provocando effetti citopatici in molte cellule, comprese quelle nervose e miocardiche. Inoltre, l'amfotericina B non è solubile; questi problemi hanno portato alla formulazione di composti liposomiali, in grado di solubilizzare l'amfotericina B e prevenirne la tossicità. Nonostante questi problemi, l'amfotericina B è l'antimicotico più utilizzato.

38. Antibiotici che agiscono sulle membrane Amphotericin B is a polyene antifungal drug, produced by S. nodosus Nistatina prodotta da S. noursei It binds with ergosterol, a component of fungal cell membranes, forming a transmembrane channel that leads to monovalent ion (K+, Na+, H+ and Cl−) leakage, leading to fungal cell death. Ergosterol is fairly unique to fungi, so the drug does not have such catastrophic effects on animals or plants. Bacteria are not affected as their cell membrane does not contain sterols.

39. Antibiotici che agiscono sulle membrane Nisin is a polycyclic antibacterial peptide with 34 amino acid residues used as a food preservative. Produced by Lactococcus lactis. Nisin is a rare example of a "broad-spectrum" bacteriocin effective against many Gram-positive organisms. Gram-negative bacteria are protected by their outer membrane.

40. Antibiotici che agiscono sulle membrane Daptomycin is a lipopeptide antibiotic naturally occurring compound found in the soil saprotroph Streptomyces roseosporus. Daptomycin is bactericidal against Gram-positive bacteria only. 

41. Polypeptides Cyclic peptides with a long hydrophobic tail. They disrupt the structure of the bacterial cell membrane by interacting with its phospholipids. They are produced by NRPS in Paenibacillus polymyxa and are selectively toxic for Gram-negative bacteria due to their specificity for the lipopolysaccharide molecule that exists within many Gram-negative outer membranes.

42. Rifampin/rifampicin This semi-synthetic antibiotic binds to the bacterial RNA polymerase and prevents it from carrying out its role in transcription. Its affinity for the equivalent eukaryotic enzyme is much lower. Composto semisintetico derivato da Amycolaptosis mediterranei .

43. Resistenza alla Rifanpicina

44. Annual worldwide production and use of antibiotics. Each year more than 500 metric tons of chemotherapeutic agents are manufactured.

45. The mass production of antibiotics began during World War II with streptomycin and penicillin. Now most antibiotics are produced by staged fermentations in which strains of microorganisms producing high yields are grown under optimum conditions in nutrient media in fermentation tanks holding several thousand gallons. The MO is strained out of the fermentation broth, and then the antibiotic is removed from the broth by filtration, precipitation, and other separation methods. Production of Antibiotics

46. The production of a new antibiotic is lengthy and costly. First, the organism that makes the antibiotic must be identified and the antibiotic tested against a wide variety of bacterial species. Then the organism must be grown on a scale large enough to allow the purification and chemical analysis of the antibiotic and to demonstrate that it is unique. This is a complex procedure because there are several thousand compounds with antibiotic activity that have already been discovered, and these compounds are repeatedly rediscovered.

47. After the antibiotic has been shown to be useful in the treatment of infections in animals, larger-scale preparation can be undertaken. Commercial development requires a high yield and an economic method of purification. Extensive research may be needed to increase the yield by selecting improved strains of the organism or by changing the growth medium. The naturally fermented product may be modified chemically to produce a semisynthetic antibiotic.

48. Once these steps have been completed, the manufacturer may file an Investigational New Drug Application with the Food and Drug Administration (FDA). If approved, the antibiotic can be tested on volunteers for toxicity, tolerance, absorption and excretion. If subsequent tests on small numbers of patients are successful, the drug can be used on a larger group, usually in the hundreds. If all goes well the drug can be used in clinical medicine. These procedures, from the time the antibiotic is discovered in the laboratory until it undergoes clinical trial, usually extend over several years.

49. Gli antibiotici possono avere effetto batteriostatico, battericida o batteriolitico. MIC: minima concentrazione inibente, che impedisce la crescita di un MO MLC: minima concentrazione letale, che uccide il patogeno

50. Test di diffusione su dischetto Metodo di Kirby-Bauer