Antimicrobial Drugs

1. Antimicrobial Drugs Prepared by Ass.Prof.Dr.Wasan A. Bakir Dep. Medical Microbiology

2. Antimicrobial Drugs • the drugs used to fight infection are called either antimicrobial or anti-infective. Or is a substance produced by various species of microorganisms that is capable in small concentrations to killing or inhibiting the growth of other microorganisms. We usually classify them according to the organism they are effective against or by their mechanism of action: • Antibacterial • Antiviral • Antifungal • Antiprotozoan • Antihelmintic • antiparasitic

3. History and Development ofAntimicrobial Drugs The development of antimicrobial drugs began in the late 1800's with Paul Erlich, a German scientist, who discovered that arsenic compounds were an effective treatment for syphilis. Unfortunately, these compounds were also highly toxic to the patients they were being used to treat. In 1928 Sir Alexander Fleming accidentally stumbled upon the discovery of the wonder drug, penicillin. As he was inspecting a plate of Staphylococcus aureuscontaminated with the mold Penicillium, Fleming noticed that the mold had inhibited the growth of the bacterial colonies. He later isolated the compound responsible for this inhibition and named it penicillin. The first sulfa drug, sulfanilamide, was discovered in 1932 by the German chemist,Gerhard Domagk

4. History and Development ofAntimicrobial Drugs • Development of new generation of drugs • In 1960s scientists alteration of drug structure gave them new properties • Penicillin altered to create ampicillin • Broadened spectrum of antimicrobial killing

5. Features of Antimicrobial Drugs • Most modern antibiotics come from organisms living in the soil • Includes bacterial species Streptomyces and Bacillus as well as fungi Penicilliumand Cephalosporium

6. Features of Antimicrobial Drugs 1-Not Allergic Reactions: some people develop hypersensitivities to antibiotics. 2- Not Toxic Effects: some antibiotics toxic at high concentrations or cause adverse effects 3- Not Suppression of normal flora: when normal flora killed, other pathogens may be able to grow to high numbers

7. Features of Antimicrobial Drugs • Selective toxicity • Antibiotics cause greater harm to microorganisms than to human host. • Inhibition of growth of m.o without damage to the host. • ex: penicillins and cephalosporins are effective antibacterial agents because they prevent the synthesis of peptidoglycan, thereby inhibiting the growth of bacterial but not human cells.

8. Antimicrobial drugs can be classified as: • Bacteriocidal drugs • Kill bacteria • Most useful in situations when host defenses cannot control pathogen • Bacteriostatic drugs • Inhibit bacterial growth • rely on host immunity

9. Bactericidal and bacteriostatic activity of antimicrobial drugs. Either a bactericidal or a bacteriostatic drug is added to the growing bacterial culture at the time indicated by the arrow. After a brief lag time during which the drug enters the bacteria, the bactericidal drug kills the bacteria, and a decrease in the number of viable bacteria occurs. The bacteriostatic drug causes the bacteria to stop growing, but if the bacteriostatic drug is removed from the culture, the bacteria resume growing.

10. Features of Antimicrobial Drugs • Spectrum of activity • Narrow spectrum • Work on narrow range of microorganisms • Gram-positive only OR Gram-negative only • Advantage: effects pathogen only • Disadvantage: requires identification of pathogen • Broad spectrum • Antibiotic are active against several types of m.o • Advantage: Work on broad range of microorganisms • Disadvantage : disruption of normal flora

11. Effects of combinations of antimicrobial drugs • Combination sometimes used to treat infections • Two or more antibiotics are used under certain circumstances, such as to • treat life-threatening infections before the cause has been identified. • to prevent the emergence of resistant bacteria during prolonged treatment regimens. • to achieve a synergistic (augmented) effect.

12. Synergism:the effect of the two drugs together is significantly greater than the sum of the effects of the two drugs acting separately. 1- Sulfonamide +Trimethoprim these two drugs may block a microbial metabolic pathway. Sulfonamide inhibit the use of extracelluar P-amino benzoic acid for the synth, of folic acid in some bact. Trimethoprim inhibit the next metabolic step. 2- Pencillin+ Gentamicin. A cell wall inhibitor may enhance the entry of Gentamicin, or streptomycin into bact. that act on protein synthesis. 3- Polymixin+ Trimethoprim one drug affect cyto. Memb. And facilitate the entry of 2nd drug. 4- One drug may prevent the inactivation of a second (inhibitors of β- lactamase as calvulanic acid can protect amoxicillin for inactivation by β- lactamase).

13. Antibiotic antagonism   occur when the antibiotic effect of a dual administration is less  than the antibiotic efficiency of the mosteffective of the  individual drugs. It occurred when a bacteriostatic drug (which inhibited protein synthesis in bacteria) such as chloramphenicol or tetracycline was given with a bactericidal drug such as a penicillin or an aminoglycoside. Antagonism occurred mainly if the bacteriostatic drug reached the site of infection before the bactericidal drug, if the killing of bacteria was essential for cure, and if only minimal effective doses of either drug in the pair were present. Another example is combining β-lactam drugs in treatment of P aeruginosainfections (eg, imipenem and piperacillinbecause imipenem is a potent β-lactamase inducer and the β-lactamase breaks down the less stable piperacillin).

14. Type of Antimicrobial Chemotherapeutic Agents drugs 1-Synthetic drugs (agents):- They synthesized chemically. For example (sulfonamides, Imidazoles, Metronidazoles, Isoniazid, Nalidixic acid, Nitrofurantion). 2-Natural products (antibiotics):- These substance of microbial origin, i.e., synthesized by the microb; and have antimicrobial action, So these antibiotic produced by fungi or bacteria or even plants such as algae.

15. Examples of antibiotic from fungi are Penicillin's and cephalosparins. -Examples of antibiotic from bacteria are Bacitracin and Polymyxins. -Examples of antibiotic from streptomyces species are Tetracyclin, Choloramphenicol, erythromycin, Streptomycin, Vancomycin, Kanamycin, lincomycin, Cycloserine and Polyenes….etc.

16. Features of Antimicrobial Drugs • Adverse effects • Allergic reactions • Toxic effects • Suppression of normal flora • Antimicrobial resistance

17. Mechanisms of Action of Antibacterial Drugs • Mechanism of action include: 1- Inhibition of cell wall synthesis • Penicillins, Cephalosporins, Vancomycin, Bacitracin 2- Inhibition of protein synthesis • Aminoglycosides, tetracyclines, macrolides, chloramphenicol, lincosamides 3- Inhibition of nucleic acid synthesis • Fluoroquinolones, rifamycins 4- Inhibition of metabolic pathways • Sulfonamides, trimethoprim 5- Interference with cell membrane integrity and function (alteration of cell membrane permeability or inhibition of active transcription) Polymyxin

18. the action of Antimicrobial Drugs

19. Mechanisms of Action: Cell Wall Synthesis • Inhibition of cell wall synthesis • Antimicrobials that interfere with the synthesis of peptidoglycan inhibit early steps in the biosynthesis of peptidoglycan. • Antimicrobials of this class include • β lactam drugs (penicillin, cephalosporin) • Vancomycin • Bacitracin

20. Mechanisms of Action: Cell Wall Synthesis • Drugs vary in spectrum • Some more active against Gram (+) • Some more active against Gram (-) • Resistance through production of β-lactamase enzyme • Penicillins + β lactamase inhibitor • Augmentin = amoxicillin + clavulanic acid The difference in susceptibility of G+ve and G-ve bacteria to penicillins or cephalosporins depends or structural difference in their cell wall a-amount of peptidoglycan b-Presence of receptors c-lipid nature of cross linking d-activity of autolytic enzymes.

21. Penicillin • Natural and semisynthetic penicilins contain β-lactam ring • Natural penicillinsproduced by Penicilliumare effective against Gram + cocci and spirochetes • Semisynthetic penicillins: made in laboratory by adding different side chains onto β-lactam ring

22. Mechanisms of Action: Cell Wall Synthesis • Vancomycin • Vancomycin is a glycopeptide (i.e., it is not a β-lactam drug), but • its mode of action is very similar to that of penicillins and • cephalosporins (i.e., it inhibits transpeptidases).

23. Inhibits formation of glycan chains • Does not cross lipid membrane of Gram (-) • Important in treating infections caused by penicillin resistant Gram (+) organisms. • Given intravenously due to poor GI absorption.

24. Mechanisms of Action: Cell Wall Synthesis • Bacitracin • Interferes with transport of PTG precursors across cytoplasmic membrane (They act by blocking the peptidoglycan by inhibition of transpeptidation). • Toxicity limits use to topical applications

25. Drugs that inhibit cell membranefunction 1-Polymyxins:- It act by binding to membrane rich in phosotidyl ethanolamine leading to disruption of cell membrane. 2-Amphotericin B, Nystatin:- The act by binding to membrane sterol. 3-Imidazoles:- They act by preventing the biosynthesis of the membrane lipid.

26. Mechanisms of Action: Protein Synthesis • Inhibition of protein synthesis • Structure of prokaryotic ribosome acts as target for many antimicrobials of this class • Drugs of this class include • Aminoglycosides • Tetracyclins • Macrolids • Chloramphenicol • Lincosamides • Oxazolidinones • Streptogramins

27. Mechanisms of Action: Protein Synthesis • Aminoglycosides • Irreversibly binds to 30S ribosomal subunit • Blocks initiation translation • Causes misreading of mRNA • Often used in synergistic combination with β-lactam drugs • Examples include • Gentamicin, streptomycin and tobramycin • Side effects with extended use include • Nephrotoxicity • Oto toxicity

28. Mechanisms of Action: Protein Synthesis • Tetracyclins • Reversibly bind 30S ribosomal subunit • Blocks attachment of tRNA to ribosome • Prevents continuation of protein synthesis

29. Mechanisms of Action: Protein Synthesis • Macrolids • Reversibly binds to 50S ribosome • Prevents continuation of protein synthesis • Effective against variety of Gram (+) organisms • Often drug of choice for patients allergic to penicillin • Macrolids include • Erythromycin, clarithromycin and azithromycin

30. Mechanisms of Action: Protein Synthesis • Chloramphenicol • Binds to 50S ribosomal subunit • Prevents peptide bond formation • Wide spectrum • Rare but lethal side effect is aplastic anemia

31. Mechanisms of Action: Protein Synthesis • Lincosamides: clindamycin • Binds to 50S ribosomal subunit • Prevents continuation of protein synthesis • Inhibits variety of Gram (+) and Gram (-) organisms • Useful in treating infections from intestinal perforation • Especially effective against Bacterioides fragilis and Clostridium difficile

32. Mechanisms of Action: DNA Replication • Fluoroquinolones Inhibit action of topoisomerase DNA gyrase(Topoisomerase maintains supercoiling of DNA) Inhibition of DNA synthesis. • Broad-Spectrum: Effective against Gram (+) and Gram (-) • Examples include • Ciprofloxacin and ofloxacin - Actinomycin:- it act by formation of complex with DNA. - Mitomycin:- it act by blocking DNA replication.

33. Mechanisms of Action: RNA Synthesis • Rifamycins • Block prokaryotic RNA polymerase • Broad-spectrum: Effective against many Gram (+) and some Gram (-) as well as Mycobacterium • Treatment of • Tuberculosis • N. meningitidis meningitis

34. Mechanisms of Action: Inhibition of Metabolic Pathways • Folate inhibitors • Mode of actions to inhibit the production of folic acid • Antimicrobials in this class include • Sulfonamides • Trimethoprim • Human cells lack specific enzyme in folic acid pathway - Sulfonamides:- they act by inhibition of the formation of folic acid from P-amino benzoic acid(PABA) by competition with PABA. - Trimethoprim:- it act by inhibition of dihydrofolatereductase.

35. Additional Drug Mechanisms Isoniazid: (INH), is a bactericidal drug highly specific for Mycobacterium tuberculosis and other mycobacteria. It is used in combination with other drugs to treat tuberculosis and by itself to prevent tuberculosis in exposed persons. Because it penetrates human cells well, it is effective against the organisms residing within macrophages. Metronidazole: is effective against anaerobic bacteria and certain protozoa. It also forms toxic intermediates that damage DNA.

36. Selection of antibiotic it depends on 1-Etiological diagnosis (the causative microorganism). 2-Susseptilbity test of organism to the antibiotic in the lab.

37. Determining Susceptibility of Bacterial to Antimicrobial Drug • MIC = Minimum Inhibitory Concentration A. Dilution test • Quantitative test to determine lowest concentration of drug that prevent growth of specific organism

38. Measurement of antimicrobial activity Dilution method: The MIC is determined by inoculating the organism isolated from the patient into a series of tubes or cups containing twofold dilutions of the drug. After incubation, the lowest concentration of drug that prevents visible growth of the organism is the MIC. To determine whether that concentration of drug is bactericidal (i.e., to determine its MBC), an aliquot (0.1 mL) from the tubes is plated on an agar plate that does not contain any drug. The concentration of drug that inhibits at least 99.9% of the bacterial colonies is the MBC.

39. Determining Susceptibility of Bacterial to Antimicrobial Drug • A second method of determining antibiotic sensitivity is the B. Kirby-Bauer disc diffusion method or disk diffusion method, in which disks impregnated with various antibiotics are placed on the surface of an agar plate that has been inoculated with the organism isolated from the patient. After incubation, during which time the antibiotic diffuses outward from the disk, Clear zone of inhibition around disc reflects susceptibility. size of clearing zone indicates if susceptible or resistant

40. Determining Susceptibility of Bacterial to Antimicrobial Drug C. E-test • Uses strips impregnated with gradient concentration of antibiotic • Test organism will grow and form zone of inhibition • Zone is tear-drop shaped • Zone will intersect strip at inhibitory concentration

41. Resistance to Antimicrobial Drugs • Mechanisms of resistance • Drug inactivating enzymes • Bacteria produce enzymes that inactivate the drug (ex., β-lactamases can inactivate penicillins and cephalosporins by cleaving the β-lactam ring of the drug). • Alteration of target molecule • Changes in ribosomal RNA prevent macrolids from binding to ribosomal subunits • Bacteria reduce permeability to the drug ex., changes in porins can reduce the amount of penicillin entering the bacterium

42. Determining Susceptibility of Bacterial to Antimicrobial Drug • Mechanisms of resistance • Increased elimination of the drug • Some organisms produce efflux pumps • Tetracycline resistance

43. Resistance to Antimicrobial Drugs • Acquisition of resistance • Can be due to spontaneous mutation • Or acquisition of new genes • Plasmid mediated

44. Resistance to Antimicrobial Drugs • Spontaneous mutation • Example of spontaneous mutation • Resistance to streptomycin is result a change in single base pair encoding protein to which antibiotic binds • When antimicrobial has several different targets it is more difficult for organism to achieve resistance through spontaneous mutation

45. Resistance to Antimicrobial Drugs • Acquisition of new genes through gene transfer • Most common mechanism of transfer is through conjugation • Transfer of R plasmid • Plasmid often carries several different resistance genes • Organism acquires resistance to several different drugs simultaneously

46. Resistance to Antimicrobial Drugs • Slowing emergence and spread of resistance • Responsibilities of physicians and healthcare workers • Prescribe antibiotics for specific organisms • Educate patients on proper use of antibiotics • Responsibilities of patients • Follow instructions carefully • Complete prescribed course of treatment • Misuse leads to resistance

47. Hospital-acquired infections are significantly more likely to be caused by antibiotic-resistant organisms than are community-acquired infections. This is especially true for hospital infections caused by Staphylococcus aureusand enteric gram-negative rods such as Escherichia coli and Pseudomonas aeruginosa. Antibiotic-resistant organisms are common in the hospital setting because widespread antibiotic use in hospitals selects for these organisms. Furthermore, hospital strains are often resistant to multiple antibiotics. This resistance is usually due to the acquisition of plasmids carrying several genes that encode the enzymes that mediate resistance.

48. Chemoprophylaxis: administration of antimicrobial to prevent infection as in : 1-Personse exposed to a specific pathogen. 2-Persone of increased susceptibility. a-Heart disease. b-RT disease. c-Recurrent UTI. d-immunocompromised patients 3-prior to surgery

49. PROBIOTICS PROBIOTICS are living microorganisms that, when taken by mouth, benefit your health by improving the balance of bacteria in the intestines. These microorganisms are most often bacteria, but also include other kinds of organisms such as yeast. Probiotics are similar, or the same as the “good bacteria” already in your body, particularly those in your gut. The normal human intestinal tract contains 300-1,000 different kinds of bacterial species.

50. Probiotics have been most commonly used when the bacterial balance of the GI tract has been disrupted by the use of antibiotics (which deplete nearly all the bacteria in your GI tract) or when “bad” bacteria (such as C. difficile) that for various reasons have overgrown in your GI tract and can cause illness. When you take antibiotic, they can disrupt the bacterial balance by not only killing the bad bacteria in the GI tract, but by also wiping out the beneficial bacteria. Probiotics help restore a healthy balance by adding “good” bacteria back to the gut and reducing the growth of any “bad” bacteria.