1. Week 13:  Antimicrobial Drugs Tuesday, June 9, 2015 Biochemistry, Microbiology and Immunology

2. Antimicrobial Drugs Chemicals used to treat microbial infections Before antimicrobials, large number of people died from common illnesses Now many illnesses easily treated with antimicrobials However, many antimicrobial drugs are becoming less useful

3. Antimicrobial Drugs Chemotherapeutic agent: Drugs that act against disease Antimicrobial drug: Drugs that treat infections Different types of antimicrobial drugs: –Antibacterial drugs –Antifungal drugs –Antiprotozoan drugs: The protozoans, unlike bacteria and fungi, do not have a cell wall. They have a nucleus and a cytoplasm that is surrounded by a selectively permeable cell membrane. The cytoplasm contains organelles similar to those found in other animal and plant cells (e.g., mitochondria, Golgi apparatus, and endoplasmic reticulum). Thus, most of the antibiotics effective in inhibiting bacteria are not active against protozoans. –Antihelminthic drugs (parasitic worms)

5. Paul Ehrlich He observed that certain dyes stain bacterial cells and not animal cells Theorized that there could be a dye or chemical that would harm bacterial cells but not human cells Systematic search for chemical to cure syphilis 606 th compound tested proved to be highly effective in treating laboratory animals

6. Gerhard Domagk Prontosil resulted from research, directed by German chemist and pathologist Gerhard Domagk, on the antibacterial action of azo dyes. A red azo dye of low toxicity, Prontosil was shown by Domagk to prevent mortality in mice infected with Streptococcus bacteria. The dye was also effective in controlling Staphylococcus infections in rabbits. Within a relatively short period, it was demonstrated that Prontosil was effective not only in combating experimental infections in animals but also against streptococcal diseases in humans, including meningitis and puerperal sepsis.Gerhard Domagkazo dyesmeningitis Later it was found that Enzymes in animals’ blood split Prontosil molecule into sulfonamide- this acted against streptococcal. Prontosil has been replaced in clinical use by newer sulfonamide drugs, including sulfanilamide, sulfathiazole, sulfamethoxazole, and other Slpha drugs.

7. Alexander Fleming Penicillin was discovered by chance, after Fleming accidentally left a dish of staphylococcus bacteria uncovered for a few days. He returned to find the dish dotted with bacterial growth, apart from one area where a patch of mould (Penicillin notatum) was growing. The mould produced a substance, named penicillin by Fleming, which inhibited bacterial growth and was later found to be effective against a wide range of harmful bacteria. However, it was not until World War II that penicillin, the first antibiotic, was finally isolated by Howard Florey and Ernst Chain. Fleming, Florey and Chain received a Nobel prize in 1945, for their discovery which revolutionised medicine and led to the development of lifesaving antibiotics.

8. Figure 20.1

9. Features of Antimicrobial Drugs Most modern antibiotics come from species of microorganisms that live in the soil To commercially produce antibiotic: 1.Select strain and grow in broth 2.When maximum antibiotic concentration reached, extract from medium 3.Purify 4.Chemically alter to make it more stable

10. Features of Antimicrobial Drugs: Selective Toxicity Cause greater harm to microorganisms than to host Chemotherapeutic index= lowest dose toxic to patient divided by dose typically used for therapy

11. Features of Antimicrobial Drugs: Antimicrobial Action Bacteriostatic: inhibit growth of microorganisms Bactericidal: Kill microorganisms

12. Features of Antimicrobial Drugs: Spectrum of Activity Antimicrobial medications vary with respect to the range of microorganisms they kill or inhibit Some kill only limited range : Narrow- spectrum antimicrobial While others kill wide range of microorganisms: Broad-spectrum antimicrobial

14. Features of Antimicrobial Drugs: Effects of Combining Drugs Combinations are sometimes used to fight infections Synergistic: action of one drug enhances the activity of another Antagonistic: activity of one drug interferes with the action of another

15. Routes of Administration – Topical application of drug for external infections – Oral route requires no needles and is self- administered – Intramuscular administration delivers drug via needle into muscle – Intravenous administration delivers drug directly to bloodstream – Know how antimicrobial agent will be distributed to infected tissues

16. The effect of route of administration on blood levels of a chemotherapeutic agent Administration method Oral Intramuscular (IM) Continuous intravenous (IV) Time (hours) Relative concentration of drug in blood

17. Clinical Considerations in Prescribing Antimicrobial Drugs Safety and Side Effects –Toxicity Cause of many adverse reactions poorly understood Drugs may be toxic to kidneys, liver, or nerves Consideration needed when prescribing drugs to pregnant women –Allergies Allergic reactions are rare but may be life threatening such as Anaphylactic shock

18. Some side effects resulting from toxicity of antimicrobial agents

19. Features of Antimicrobial Drugs: Adverse Effects 1.Allergic Reactions: some people develop hypersensitivities to antimicrobials 2.Toxic Effects: some antimicrobials toxic at high concentrations or cause adverse effects 3.Suppression of normal flora: when normal flora killed, other pathogens may be able to grow to high numbers

20. Features of Antimicrobial Drugs: Resistance to Antimicrobials Some microorganisms inherently resistant to effects of a particular drug Other previously sensitive microorganisms can develop resistance through spontaneous mutations or acquisition of new genes

21. Mechanisms of action of Antibacterial Drugs 1.Inhibit cell wall synthesis 2.Inhibit protein synthesis 3.Inhibit nucleic acid synthesis 4.Injury to plasma membrane 5.Inhibit synthesis of essential metabolites

22. Figure 20.2

23.  Lactam Drugs- inhibit cell wall synthesis Irreversibly inhibit enzymes involved in the final steps of cell wall synthesis These enzymes mediate formation of peptide bridges between adjacent stands of peptidoglycan  lactam ring similar in structure to normal substrate of enzyme Drug binds to enzyme, competitively inhibit enzymatic activity

25.  Lactam Drugs Some bacteria produce  -lactamase- enzyme that breaks the critical  -lactam ring  -lactam drugs include: penicillins and cephalosporins

26. Antibacterial medications that inhibit protein synthesis Target ribosomes of bacteria Aminoglycosides: bind to 30S subunit of ribosome causing it to distort and malfunction; blocks initiation of translation Tetracyclines: bind to 30S subunit blocking attachment of tRNA Macrolides: bind 50S subunit and prevents continuation of protein synthesis

27. Figure 20.4b

28. Antibacterial medications that inhibit nucleic acid synthesis Target enzymes required for nucleic acid synthesis Fluoroquinolones: inhibit enzymes that maintain the supercoiling of closed circular DNA Rifamycins: block prokaryotic RNA polymerase from initiating transcription

29. Antibacterial medications injure plasma membrane Polymyxin B: binds to membrane of G- bacteria (gram +, gram-) and alters permeability This leads to leakage of cellular contents and cell death These drugs also bind to eukaryotic cells to some extent, which limits their use to topical applications

30. Antibacterial drugs that inhibit synthesis of essential metabolites Competitive inhibition by substance that resembles normal substrate of enzyme Sulfa drugs

31. Antiviral Drugs Very few antiviral drugs approved for use in US Effective against a very limited group of diseases Targets for antiviral drugs are various points of viral reproduction

32. Nucleoside and Nucleotide analogs Acyclovir- used to treat genital herpes Cidofovir- used for treatment of cytomegaloviral infections of the eye Lamivudine- used to treat Hepatitus B

35. Antiretrovirals Currently implies, a drug used to treat HIV Tenofovir- nucleotide reverse transcriptase inhibitor Zidovudine- nucleoside analog

36. Other enzyme inhibitors Zanamivir (Relenza) and Oseltamivir phosphate (Tamiflu)- inhibitors of the enzyme neurominidase –Used to treat influenza Indinavir- protease inhibitors

37. Interferons Interferons inhibit further spread of the infection Alpha-interferon- drug for treatment of viral hepatitis infections

38. Antifungal drugs Since fungi are eukaryotic, it is more difficult to find point of selective toxicity in eukaryotes than in prokaryotes Targets of antifungal drugs: –Agents affecting fungal sterols –Agents affecting fungal cell walls –Agents inhibiting nucleic acids

39. Agents affecting fungal sterols Many antifungals target the sterols in the plasma membrane Polyenes- used in systemic fungal infections, very toxic to kidneys Azoles- used for athlete’s foot and vaginal yeast infections (miconizole)

40. Agents affecting fungal cell walls Primary target of selective toxicity is β- glucan Inhibition of synthesis of this glucan results in an incomplete cell wall, and results in lysis of the cell Caspofungin- first new class of antifungals in 40 years

41. Agents inhibiting nucleic acids Flucytin- nucleotide analog of cytosine, interferes with the biosynthesis of RNA, and therefore protein synthesis

42. Antiprotozoan drugs Quinine is the major one that still is used to control malaria Chloroquinone- synthetic derivative of Quinine that has largely replaced it Mefloquinone- used in areas where resistance to chloroquinone has developed Quinacrine- drug of choice for treating protozoan disease, giardiasis (is an intestinal infection caused by a microscopic, single-celled parasite known as Giardia lamblia).

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44. Antihelminthic drugs Praziquantel- used in treatment of tapeworms; kills worms by altering permeability of plasma membranes

45. Clinical Considerations in Prescribing Antimicrobial Drugs Efficacy –Ascertained by Diffusion susceptibility test Minimum inhibitory concentration test Minimum bactericidal concentration test

46. Kirby-Bauer method for determining drug susceptibility 1.Bacteria spread on surface of agar plate 2.10-12 disks, each with different antimicrobial drug, placed on agar plate 3.Incubated- drugs diffuse outward and kill susceptible bacteria 4.Zone of inhibition around each disk 5.Compare size of zone to chart

47. Zones of inhibition in a diffusion susceptibility (Kirby-Bauer) test Bacterial lawnZone of inhibition

48. Minimum inhibitory concentration (MIC) test in test tubes Turbid tubesClear tubes Increasing concentration of drug

49. An Etest combines aspects of Kirby-Bauer and MIC tests

50. A minimum bactericidal concentration (MBC) test Clear MIC tube Concentration of antibacterial drug (µg/ml) 8 µg/ml16 µg/ml25 µg/ml Bacterial coloniesNo colonies Drug-free media

51. Resistance to antimicrobial drugs Drug resistance limits use of ALL known antimicrobials Penicillin G: first introduced, only 3% of bacteria resistant Now, over 90% are resistant

53. Slowing the emergence and spread of antimicrobial resistance 1.Responsibilities of Physicians: must work to identify microbe and prescribe suitable antimicrobials, must educate patients 2.Responsibilities of Patients: need to carefully follow instructions

54. Slowing the emergence and spread of antimicrobial resistance 3. Educate Public: must understand appropriateness and limitations of antibiotics ; antibiotics not effective against viruses 4. Global Impacts: organism that is resistant can quickly travel to another country - in some countries antibiotics available on non-prescription basis - antibiotics fed to animals can select for drug- resistant organisms

56. New Approaches to Antibiotic Therapy Are Needed Scientists work to find new antibiotic targets in pathogens Discovery of new and unique antibiotics is necessary