control microbial growth in vivo

Transcription

1 control microbial growth in vivo ANTIMICROBIAL CHEMOTHERAPY Dr. Faten Mostafa Professor of Medical Microbiology & Immunology, Faculty of Medicine, Ain Shams University 11/6/2016 Dr Faten Mostafa 1

2 In vitro control microorganisms involve either chemical or physical agents. in vivo Chemotherapeutic agents (antimicrobials) are chemical substances that destroy or inhibit the growth of microorganisms in living tissues

3 ILOs At the end of this chapter you should be able to: 1-Discuss different methods to control microbial growth in vivo and in vitro 3-Define antimicrobial agent, bactericidal agent, bacteristatic agent, narrowspectrum and broadspectrum antibacterial agents. 4-Classify different antimicrobial agents according to their mechanism of action. 5-Understand mechanisms of action of different antifungal drugs.

4 6-Prescribe prophylactic antimicrobials only in proper situations. 7-Determine when to prescribe surgical antimicrobial prophylaxis. 8-Discuss the hazards of unnecessary administration of long term course ofantimicrobial treatment. 9-List different mechanisms involved in antimicrobial drug resistance. 10-Know how and when to apply antimicrobials in combinations.

5 Definitions Antimicrobial agents Naturally antibiotic antibiotic kill or inhibit systemic use any antimicrobial agent whether naturally or synthetically produced. "Chemotherapeutic antimicrobial substance is synthesized in laboratory secondary metabolites produced by living bacteria (e.g. Streptomyces, Bacillus) molds (e.g. Penicillium,Cephalosporium), &is effective against other microorganisms 5

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7 Definitions "Bactericidal agent" "Bacteriostatic agent -antimicrobial agent that affects bacteria by killing them, e.g. penicillins. -Multiplication can not be resumed upon removal of the agent. -inhibition of growth &multiplication of bacteria, e.g. Sulfonamides. -Multiplication can be resumed upon removal of the agent. 11/6/2016 Dr Faten Mostafa 7

8 Definitions either Gram negative or Gram positive bacteria). Gram-negative and Gram-positive organisms 11/6/2016 Dr Faten Mostafa 8

9 ANTIMICROBIAL or antibiotics Prophylactic Use Mechanisms of Action Complications of Chemotherapy Antifungal Agents Resistance to Antimicrobial Drugs Ideal Antimicrobial 11/6/ Mechanisms of Drug Resistance

10 Mechanisms of Action of Antimicrobial drugs 11/6/2016 Dr Faten Mostafa 10

11 Selective Toxicity Drug kills pathogens without damaging the host. Based on differences in cellular chemistry of mammals and microbes 11/6/2016 Dr Faten Mostafa 11

12 Mechanism of action of antibacterial agents Kill growing bact 11/6/2016 Dr Faten Mostafa 12

13 1- Inhibition of Bacterial Cell Wall Synthesis Action Resistant bacteria selective toxicity Mycoplasmas & L-forms -Inhibit synthesis of PG Found only in cell wall of bacteria -internal osmotic pressure of bacteria is high, they will take up water rapidly and explode, causing bacteriolysis. Absence of cell wall in host cell 11/6/2016 Dr Faten Mostafa 13

14 Examples of these antimicrobial agents -lactam drugs Penicillins cephalosporins cycloserine bacitracin Glycopeptides (vancomycin, teicoplanin) Monobactam (Aztreonam) All carbapenems act by inhibiting cross-linking of PG strands which is the last steps of PG synthesis that give the cell wall its strength All Act by inhibit early steps in PG synthesis that take place inside cytoplasmic membrane 14

15 Composition of cell wall

16 Action of penicillin transpeptidase enz which catalyse cross-linking of PG strands Autolytic enzyme are activated in pecilin treated cell Bind to PBP in bact CW some are transpeptidase enz other function in PG synthesis 11/6/2016 Dr Faten Mostafa 16

17 Resistance B lactam B lactamase

18 Spectrum of activity Penicillins cephalosporins carbapenems Gram+ve Gram+ve &-ve Gram+ve &-ve Monobactam Gram-ve & anaerob

19 Vancomycin block binding of Tpase Peniciilin bind to Tpase restricted spectrum to Gram+ve bacteria. Note -lactam drugs used successfully in infections caused by methicillin-resistant Staphylococcus aureus (MRSA). 11/6/2016 Dr Faten Mostafa 19

20 Penicillin End with icillin Methicillin, Nafcillin, Amoxicillin, Ampicillin, 11/6/2016 Dr Faten Mostafa 20

21 cephalosporin Start with Cef cefazolin, cefoxitin, cefotaxime, cefepime 11/6/2016 Dr Faten Mostafa 21

22 2- Interference with CM Function Action CM of bacteria and fungi has a structure different from that of mammalian cells selective toxicity -does not contain sterol -Disruption of CM &interfere with its function. -Macromolecules &ions escape from cell resulting in cell death. -Drugs are microbicidal, &highly toxic, -Are used for topical applications only. Examples Antibacterial drugs Antifungal drugs 11/6/2016 Polymyxin B, Colistin Amphotericin B, Imidazoles, Nystatin.

23 .3-Inhibition of Protein Synthesis selective toxicity ides Action Examples bacterial ribosomes are 70s(30s-50s) Act on 30S Act on 50S Chloramphenicol, macrolides(erythromycin),azalides(azithromycin), Lincomycin clindamycin 11/6/2016 streptomycin gentamycin amikacin tobramycin tetracyclines doxycycline minocycline

24 TO REMEMBER them CLEAn TAG C for Chloramphenicol and Clindamycin L for Linezolid, Lincomycin E for Erythromycin (macrolides) A for azalides (Azithromycin T for Tetracyclines AG for Aminoglycosides CLEAn act on the 50S subunit of bacterial ribosome. TAG act on the 30S subunit of bacterial ribosome 24 A

25 Aminoglycosides End with mycin except amikacin Streptomycin Gentamycin Tobramycin. 11/6/2016 Dr Faten Mostafa 25

26 Tetracyclines End with cycline Doxycycline Minocycline 11/6/2016 Dr Faten Mostafa 26

27 Ag active Gram ve Tb misreading of mrna Cidal Not absorbed fro GIT poor penetration to spinal fluid Toxic to kidney 8 th cranial nerve Tetra static Gram ve & Gram +ve Chlora Gram ve & Gram +ve Peptidyl transferase Macro clinda static Linezoild cidal

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29 4. Inhibition of Nucleic Acid Synthesis Inhibitors of RNA synthesis Inhibitors of DNA synthesis act by inhibiting RNA polymerase of bacteria so inhibit transcription of RNA from DNA, selective?// act Directly Act precursers synthesis Indirectly rifampin 11/6/2016 -Quinolones (Nalidixic acid, ciprofloxacin, norfloxacin), -Nitroimidazoles -Novobiocin. -Sulfonamides (sulfisoxazole) -Trimethoprim. 29 Dr Faten Mostafa

30 Nitroimidazoles (metronidazole )act directly by causing strand breakage in DNA. active only against anaerobic bacteria and protozoal infections. 11/6/2016 Dr Faten Mostafa 30

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32 Quinolones Inhibit DNA gyrase End with floxacin Ciprofloxacin Norfloxacin 11/6/2016 Dr Faten Mostafa 32

33 11/6/2016 How Sulfanilamide Works to Kill Bacteria 33

34 structural analogues of PABA (competitive inhibition 11/6/2016 Dr Faten Mostafa 34

35 our cells don't make TH4, we get it as a vitamin in our diet it doesn't affect us, but it affects the bacteria. 11/6/2016 Dr Faten Mostafa 35

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39 Properties of an Ideal Antimicrobial Agent 1) Have a selective toxicity, 2) Can not be affected by body fluids. 3) Have bactericidal rather than bacteriostatic effect. 4) Have a broad spectrum activity. 5) Easily administered: orally, water-soluble. 6) Reach effective level in all body fluids, slowly excreted. 7) Does not induce allergy or hypersensitivity. 8) Microorganisms do not acquire resistance against it. 11/6/2016 Dr Faten Mostafa 39

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41 Prophylactic Use of Antimicrobials 1-Rheumatic fever 3-Meningococcal meningitis 2-Subacute bacterial endocarditis (SBE) A single large dose of amoxicillin is given prior to dental manipulation to patients with congenital or rheumatic heart disease, to preventsbe. 11/6/2016 Dr Faten Mostafa 41 rifampin is used for prophylaxis of close contacts

42 Pathogenesis of SABE

43 Prophylactic Use of Antimicrobials 4-Cholera 5-Surgical prophylaxis Tetracyclines are used as a prophylaxis to contacts orally To prevent the spread of infection to a primarily clean surgical field 11/6/2016 Dr Faten Mostafa 43

44 Criteria for Use of Surgical antimicrobial prophylaxis Systemic preventive antibiotics should be used when should have activity against pathogens likely to be encountered in procedure should be administered preoperatively, before induction of anesthesia in most situations High risk of infection is associated with the procedure (e.g., colon resection) Consequences of infection are unusually severe (e.g., total joint replacement) -Patient has a high Risk Postoperative administration beyond 24 hours has not been demonstrated to reduce the risk of surgical site infection.

45 Complications of Chemotherapy Drug Resistance Superinfection Drug Toxicity Allergy (hypersensitivity) overgrowth of Clostridium difficile causes pseudomembranous colitis.aac Antibiotic will be effective against pathogenic bacteria -suppress normal bacterial flora -overgrowth of potentially pathogenic DR microorganism -Candida leads to oral thrush or vulvovaginitis 11/6/2016 Dr Faten Mostafa drug may act as a hapten, binds to tissue proteins &stimulates an exaggerated IR leading to tissue damage penicillins cause allergic reactions (urticaria to anaphylactic shock) Local application of sulfonamides??///////simi may result in contact dermatitis. 45

46 Complications of Chemotherapy Tetracycline Drug Toxicity Streptomycin children, pregnant,old people. prolonged use toxic effects on host Overdosage Polymyxin Polymyxins Chloramphenicol

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48 Complications of Chemotherapy Drug Resistance Abuse: -low dosage, -interrupted course, resistant microorganisms -not actually indicated, will overgrow & wrong choice of replace originally antibiotic. susceptible 11/6/2016 Dr Faten Mostafa 48

49 Resistance to Antimicrobial Drugs 11/6/2016 Dr Faten Mostafa 49

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54 Resistance to Antimicrobial Drugs Intrinsic inherent or natural Enterococcus is cephalosporin resistant. abuse low dosage, interrupted course, 11/6/2016 Dr Faten Mostafa 54 Acquired not actually indicated, wrong choice

55 Intrinsic inherent natural Steptomycetes gene that protects it from the antibiotics it produces Gram-ve CM has pores too small to allow large antibiotic molecules (e.g. nafcillin) to penetrate An organism lacks the target or receptor for the antibiotic e.g. mycoplasmas to penicillins & resistance of Enterococcus species to cephalosporins 11/6/2016 Dr Faten Mostafa 55

56 Acquired abuse low dosage, interrupted course, not actually indicated, wrong choice 11/6/2016 Dr Faten Mostafa 56

57 Mechanisms of Drug Resistance an alternative metabolic pathway, that bypass reaction inhibited by drug (sulfonamides) 1-MOs produce Enzymes destroy drug an altered structural target (receptor) for drug, ICC of the antibiotic altered enzyme,still perform its metabolic function, but less affected by the drug, e.g. sulfonamide-resistant. 11/6/2016 Dr Faten Mostafa 57

58 Mechanisms of Drug Resistance -lactamases (penicillinases) produced by Staphylococci (Gram+ve) destroy penicillins &cephalosporins. 1-Microorganisms produce Enzymes destroy drug Extended spectrum β- lactamases (ESBLs aminoglvcosidesmodifying enzymes Chloramphenicol resistance due to acetyl transferase enzyme. 11/6/2016 produced by Gram- bacilli they confer resistance to Penicillins, Cephalosporins, Monobactam &aztreonam. 58

59 Mechanisms of Drug Resistance Modification of (PBPs): e.g. resistance to penicillin in pneumococci and resistance to all β -lactam antibiotics in MRSA an altered structural target (receptor) for drug, Alteration of the 30S ribosomal subunit reduces the affinity of aminoglycosides for the ribosome. (Chromosomal resistance). 11/6/ Alteration of the 50S ribosomal subunit reduces the affinity of macrolides, linezolid and streptogramins for the ribosome.

60 Reduction of IC concentration of the antibiotic Decrease in influx permeability of OM by modification or loss of porin (e.g. imipenem resistance in Pseudomonas. uptake across the CM, e.g. aminoglycosides resistance in S aureus 11/6/2016 Dr Faten Mostafa 60

61 Efflux pumps AB is pumped out across the cytoplasm membrane faster than it can diffuse in, so the concentration of antibiotic remains too low to be effective. macrolides, tetracycline, quinolones and B- lactams by organisms such as Escherichia coli, Shigella and S. aureus. 11/6/2016 Dr Faten Mostafa 61

62 Origin of Drug Resistance Non genetic origin Metabolically inactive bacteria (dormancy), Mycobacterium tuberculosis Loss of target structure for the drug ( L forms of bacteria and Mycoplasmas 11/6/2016 Dr Faten Mostafa 62

63 Origin of Drug Resistance Genetic origin Chromosomal Spontaneous mutation, resistance to streptomycin due to change in receptor located in the 30 S bacterial ribosome. Extrachromosomal Gene transfer, -lactamases which destroy -lactam ring in penicillins &cephalosporins. 11/6/2016 Dr Faten Mostafa 63

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65 Genetic Origin 1- Chromosomal: this occurs as a result of spontaneous mutation in a gene that controls the susceptibility to a given drug. This results in change in the structural receptor for the drug. 11/6/2016 Dr Faten Mostafa 65

66 Extrachromosomal: resisrance occurs through plasmids or transposons R-factors carry genes usually code for enzymes that are capable of destroying antimicrobial drug, e.g. β lactamases. Genetic material of plasmid can be transferred between bacteria by transduction, conjugation 11/6/2016 Dr Faten Mostafa 66

67 Application in Treatment Combination of two or more agents in treatment of tuberculosis, limiting selection of mutants resistant to individual components. Use of beta lactam antibiotics with an aminoglycoside in treatment of streptococcal endocarditis A combination of a beta lactam antibiotic with beta lactamase inhibitor prevent destruction of antibiotic. (combination of amoxicillin with enzyme inhibitor clavulanic acid (Augmentin ) restores activity of antibiotic against many beta lactamase-producing bacteria. 11/6/2016 Dr Faten Mostafa 67

68 Probitics Live nonpathogenic bac used in ttt or prevent human dis Exclude pathogen from binding site to mucosa enhance imm response to pathogen Oral lactobacillus rhamnosus in prevetion of NC diarrheoa or saccharomyces fot AAC