Ch 20 Chemotherapy .pdf

Chapter 20 - Antimicrobial Drugs: Chemotherapy Pseudomonas aeruginosa Pneumonia, blood infection urinary tract infections  Ch.20 – Antimicrobial Drugs: Chemotherapy o What’s chemotherapy? How do microbes cause infection? o Antibiotics o Mechanisms of Antibio...

Chapter 20 - Antimicrobial Drugs: Chemotherapy Pseudomonas aeruginosa Pneumonia, blood infection urinary tract infections  Ch.20 – Antimicrobial Drugs: Chemotherapy o What’s chemotherapy? How do microbes cause infection? o Antibiotics o Mechanisms of Antibiotics o Penicillin – the 1st antibiotic discovered o Mycobacterium – special antibiotics o Evaluating antibiotic effectiveness o Effect of antibiotic combinations o Antibiotic resistance o Antiviral drugs  Chemotherapy: the use of chemicals to treat a disease Chemotherapy Terms: o Bactericidal: kills microbes directly o Bacteriostatic: prevents growth of microbes o Selective toxicity: selectively finding and destroying pathogens without damaging the host o Antibiotic: substance produced by a microbe that, in small amounts, inhibits another microbe o Antimicrobial drugs: synthetic substances that interfere with the growth of microbes antibiotic sensitivity - disk diffusion method antimicrobial peptides – target bacterial membranes  How do bacteria damage host cells 1. Using host nutrients Siderophores: bacteria whose proteins that bind iron more tightly than host cell: many hemolytic Exotoxins are secreted Endotoxins released when cell divides or dies Siderophore 2. Direct damage: disrupt host cell function; produce waste product 3. Produce toxins: poisonous substances that induce fever, diarrhea, shock, heart problems Exotoxins: toxins secreted by bacteria; gram + mostly - destroy host cell; inhibit cell functions Endotoxins: gram neg. LPS releases toxin – called Lipid A release when bacteria divide or die Causes macrophages to release cytokines – overactive immune response – leads to sepsis  How does a virus damage host cells Virus infects by binding specific cell type and inserting its nucleic acid (DNA or RNA) into cell Cell then replicates, transcribes/translates viral nucleic acid – producing more virus New virus lysis out of cell – killing cell viral life cycle Viral Life Cycle – Infection of host cell 1. Attach to cell – via virus/cell surface receptors 2. Inserts nucleic acid 3. Cell replicates and transcribes/translates nucleic acid Nucleic acid codes for viral parts and viral assembly enzymes 4. Host and viral enzymes assemble new virus 5. New Virus assembles and leaves cell o Ultimately killing cell  different target sites of antimicrobial drugs antimicrobial drugs: o work by inhibiting cellular processes o target differences between cell types antibiotics: molecule produced by one bacteria/fungus species toxic to another bacteria/fungas species target prokaryotic or fungi specific cell characteristics  Spectrum of Antimicrobial Activity - Specificity Examples of antimicrobial spectrum of antimicrobial activity on different prokaryotes and eukaryotes *Growth of these bacteria frequently occurs within macrophages or tissue structures; †Obligately intracellular bacteria. Narrow spectrum antibiotics: affect a narrow or specific range of microbial types Broad-spectrum antibiotics: affect broad range of microbial types can affect both gram-positive or gram-negative bacteria Superinfection: secondary infection caused by earlier infection second infection is resistant to the treatment being used against the first infection.  Ch.20 – Antimicrobial Drugs: Chemotherapy o What’s chemotherapy? How do microbes cause infection? o Antibiotics o Mechanisms of Antibiotics o Penicillin – the 1st antibiotic discovered o Mycobacterium – special antibiotics o Evaluating antibiotic effectiveness o Effect of antibiotic combinations o Antibiotic resistance o Antiviral drugs  Antibiotics o molecule produced by, or a semisynthetic substance derived from, bacteria or fungus that inhibits or kills another microorganism. used to treat human bacterial and/or fungal infections can do so because they work by targeting prokaryotic or fungi specific cell characteristics Representative Sources of Antibiotics Microorganism Antibiotic Gram-Positive Rods Blank Bacillus subtilis Bacitracin Paenibacillus polymyxa Polymyxin Actinomycetes Blank Streptomyces nodosus Amphotericin B Streptomyces venezuelae Chloramphenicol Streptomyces aureofaciens Chlortetracycline and tetracycline Saccharopolyspora erythraea Erythromycin Streptomyces fradiae Neomycin antibiotic sensitivity - disk diffusion method Streptomyces griseus Streptomycin Micromonospora purpurea Gentamicin  Ch.20 – Antimicrobial Drugs: Chemotherapy o What’s chemotherapy? How do microbes cause infection? o Antibiotics o Mechanisms of Antibiotics o Penicillin – the 1st antibiotic discovered o Mycobacterium – special antibiotics o Evaluating antibiotic effectiveness o Effect of antibiotic combinations o Antibiotic resistance o Antiviral drugs Understanding antimicrobial drugs and their mechanisms of action Why is it critically important to understand these mechanisms? o Microbes are increasingly evolving resistance to current antimicrobial drugs MRSA infections Methicillin-resistant Staphylococcus aureus Staphylococcus aureus is resident skin bacteria in small % of population Nosocomial infections increasing  Infections that have historically been treatable…. Penicillin susceptible bacterial infection Before/after antibiotic treatment MRSA bacterial Infection infection treated with penicillin are increasingly becoming untreatable… Penicillin microbes are evolving drug resistance o MSRA: Methicillin-resistant Staph. aureus CDC Report: ~100,000 infected/tr. ; ~10,000 deaths/yr. Increasingly common nosocomial infection  Antimicrobial drug groups: Antibiotics: Antifungals: Antivirals: Target Bacteria Target Fungi Target Virus Antibiotics: Molecules produced by bacteria or fungus that are toxic to other bacteria or fungal species o Technical Definition: chemicals produced by bacteria or fungi that kill or prevent growth of other bacteria or fungal species o General definition: substance that inhibits growth or kills specific bacteria or fungal species Includes synthetic antibiotics`  Antibiotic sites of action: Targeting differences between bacteria (prokaryotic) and human cells (eukaryotic) DNA replication Prokaryotic cell differences: cell wall 1. Cell wall – peptidoglycan transcription unique composition DNA 2. DNA replication different replication enzymes Antibiotics 3. Transcription RNA metabolism different transcript. enzymes 4. Translation different ribosomes proteins translation 5. Metabolism unique metabolic pathways antibiotic mechanisms of action against bacteria cell  Mechanisms of Antibiotics 1. Inhibiting cell wall synthesis Penicillin's - prevent the cross-linking of peptidoglycan when build new cell wall the inhibition of bacterial cell wall synthesis by penicillin  Penicillin - Cell Wall Inhibitor 2. DNA replication inhibitor Mechanism: Blocks “strand stabilizer” of unwound DNA Inhibits DNA gyrase enzyme Penicillin mechanism: Topoisomerase does this in eukaryotes o Blocks cell wall cross-linking Inhibits enzyme that crosslinks peptidoglycan Penicillin DNA replication inhibitor mechanism of action Bactericidal/ Broad spectrum Specificity excellent: we don’t have cell walls! Ciprofloxacin (cipro) Virtually no side effects Bactericidal / Broad spectrum  3. Transcription Inhibitor 4. Translation Inhibitor Mechanisms of action: Mechanisms of action: Bind to inhibit function of RNA polymerase Bind ribosome - Inhibit tRNA binding Distort ribosome - disrupting mRNA code transcription inhibitor mechanisms of action translation mechanisms of action Tetracycline: Inhibits tRNA binding Bacteriostatic / broad spectrum Rifampin Streptomycin: bnds and distorts ribosome mRNA code can not be read Bactericidal / narrow spectrum Bactericidal / broad spectrum  Inhibiting protein synthesis Target bacterial 80S (30s / 50s) ribosomes Chloramphenicol, erythromycin, streptomycin, tetracyclines  5. Metabolism Mechanism: target nucleic acids and amino acid synthetic pathways metabolism inhibitor mechanism of action Sulfa antibiotics competitive inhibitors for enzyme that acts on PABA PABA needed for bacterial nucleotide synthesis Human cells do not use PABA to make folate PABA: para-amino-benzoic acid  Antifungal Mechanisms Fungi share a much later common ancestor with humans than bacteria There are less cell type differences; consequently more side-effects Targeting Cell Wall: 1. Inhibits cell wall synthesis Echinocandins Inhibits enzyme that synthesizes glucan Glucan part of fungal cell wall called “penicillin of antifungals” Echinocandin antifungal mechanism of action  Damaging the plasma membrane Polypeptide antibiotics - change membrane permeability combine with membrane sterols of fungal plasma membranes Injury to plasma membrane of a budding yeast cell caused by an antifungal drug  Antiviral Mechanisms o Virus is NOT living – does not metabolize Antiviral approach: Inhibit/disable viral proteins Cell attachment or viral enzymes example of reverse transcriptase inhibitor RNA virus example : Reverse Transcriptase Inhibitor (RTI) o Virus examples: HIV and Hepatitis B Reverse transcriptase converts viral RNA to DNA RTI’s bind /inhibit reverse transcriptase  Ch.20 – Antimicrobial Drugs: Chemotherapy o What’s chemotherapy? How do microbes cause infection? o Antibiotics o Mechanisms of Antibiotics o Penicillin – the 1st antibiotic discovered o Mycobacterium – special antibiotics o Evaluating antibiotic effectiveness o Effect of antibiotic combinations o Antibiotic resistance o Antiviral drugs  Penicillin – cell wall inhibitor functions by inhibiting the cell wall synthesis of gm+ bacteria o contain a β-lactam ring - common in ALL penicillin's Penicillin structure – indicating common beta-lactam ring “nucleus” o penicillin types are differentiated by the chemical side chains attached to the ring  Penicillin functions by… preventing the cross-linking of peptidoglycans…therefore, interfering with cell wall construction especially gram-positive bacteria LPS layer is protective for gram-negative bacteria penicillin mechanism of action on gram positive cell wall  Natural vs. Synthetic Penicillin’s Natural penicillin's extracted from Penicillium fungus cultures narrow spectrum of activity susceptible to penicillinases (β-lactamases) penicillinase enzymes that can inactivate penicillin; produced by certain bacteria structure of natural penicillin's structure of semisynthetic penicillin's Semi-synthetic penicillin's contain chemically added side chains, making them resistant to penicillinases  Penicillinases (β-lactamases) enzymes that can inactivate penicillin, produced by certain bacteria cleaves β-lactam ring deactivation of penicillin by penicillinase intact B-lactam ring active penicillin deactivated B-lactam ring inactive  Ch.20 – Antimicrobial Drugs: Chemotherapy o What’s chemotherapy? How do microbes cause infection? o Antibiotics o Mechanisms of Antibiotics o Penicillin – the 1st antibiotic discovered o Mycobacterium – special antibiotics o Evaluating antibiotic effectiveness o Effect of antibiotic combinations o Antibiotic resistance o Antiviral drugs  Anti-mycobacterial antibiotics: Mycobacteria contain mycolic acid in cell wall Isoniazid (INH) Inhibits the mycolic acid synthesis in mycobacteria Ethambutol Inhibits incorporation of mycolic acid into the cell wall Mycobacterium tuberculosis  Ch.20 – Antimicrobial Drugs: Chemotherapy o What’s chemotherapy? How do microbes cause infection? o Antibiotics o Mechanisms of Antibiotics o Penicillin – the 1st antibiotic discovered o Mycobacterium – special antibiotics o Evaluating antibiotic effectiveness o Effect of antibiotic combinations o Antibiotic resistance o Antiviral drugs  testing effectiveness of chemotherapeutic agents 1. Disk-diffusion method (Kirby-Bauer test) o tests the effectiveness antimicrobial disinfectants o paper disks with a disinfectant are placed on agar containing the test organism o zone of inhibition around the disk determines the sensitivity of the organism to the antibiotic “Zone of Inhibition” clear area around disk due to bacterial growth inhibition determines microbial sensitivity to disinfectant / antibiotic do not know if bactericidal or bacteriostatic unless remove disk and see if microbe grows back antibiotic sensitivity - disk diffusion method  2. E test o a gradient diffusion method that determines antibiotic sensitivity o uses special agar with low resistance to diffusion E-test gradient diffusion agar o enables determination of minimal inhibitory concentration (MIC) o lowest antibiotic concentration preventing bacterial growth  3. Broth Dilution Tests Broth dilution test o determines the MIC (minimal inhibitory concentration) o test organism is placed into the wells of a tray containing dilutions of a drug o minimum concentration to kill microbes is determined  Ch.20 – Antimicrobial Drugs: Chemotherapy o What’s chemotherapy? How do microbes cause infection? o Antibiotics o Mechanisms of Antibiotics o Penicillin – the 1st antibiotic discovered o Mycobacterium – special antibiotics o Evaluating antibiotic effectiveness o Effect of antibiotic combinations o Antibiotic resistance o Antiviral drugs  effects of drug combinations Synergism: o the effect of two drugs together is greater than the effect of either alone two antibiotic synergistic affect on bacterial lawn Synergism, Antagonism, or no effect? Synergism!!! Antagonism: o the effect of two drugs together is less than the effect of either alone  Ch.20 – Antimicrobial Drugs: Chemotherapy o What’s chemotherapy? How do microbes cause infection? o Antibiotics o Mechanisms of Antibiotics o Penicillin – the 1st antibiotic discovered o Mycobacterium – special antibiotics o Evaluating antibiotic effectiveness o Effect of antibiotic combinations o Antibiotic resistance o Antiviral drugs Why is it critically important to understand antimicrobial drug mechanisms? o Microbes are increasingly evolving resistance to current antimicrobial drugs Leading to untreatable infections An infection that starts like this… Can lead to an infection like this… MRSA Infection Major challenge to discovering effective new antimicrobial drugs o Selective toxicity: must target microbe but cause little/no effect on host cells o Antimicrobial drug approach: Target differences between cell types  resistance to antimicrobial drugs Persister cells o microbes with genetic characteristics allowing for their survival when exposed to an antibiotic Superbugs o bacteria that are resistant to large numbers of antibiotics researchers have found a person in the United States carrying bacteria resistant to antibiotics of last resort strain of E. coli resistant to the antibiotic colistin top U.S. public health official “could mean end of road” for antibiotics. bacterial cells some may be persister cells resistance genes are often spread horizontally among bacteria on plasmids via conjugation or transformation  three modes bacterial DNA transfer 3 ways bacteria transfer DNA: Transformation: process by which plasmids from environment are takin in by bacteria Conjugation: process by which plasmids are transferred between bacteria via pilus Transduction: transfer of DNA into bacteria using a “disabled” virus  five mechanisms of bacterial resistance 1. enzymatic destruction or inactivation of the drug 2. prevention of penetration to the target site within the microbe 3. alteration of the drug's target site 4. rapid efflux (ejection) of the antibiotic 5. combinations of these mechanisms of resistance` development of an antibiotic-resistant mutant during antibiotic therapy 5 mechanisms of bacterial resistance to antibiotics  Antibiotic Resistance: Today’s Epidemic Antibiotics are LOSING ability to kill bacteria o How, why? Evolution – Natural Selection is favoring antibiotic-resistant bacteria Evolutionarily….antibiotic resistance mutations are being selected for multidrug-resistant mycobacterium tuberculosis  how are we making it worse? “~30% of antibiotic prescriptions not needed give preventive” antibiotics to farm animals this “floods” the world with antibiotics INCREASING Natural Selection Pressure we are flooding world with antibiotics bacteria that survive are resistant to antibiotics! resistant bacteria multiply we are “selecting for” antibiotic resistant bacteria! antibiotic resistant cells in colony survive treatment and reproduce  antibiotic misuse misuse of antibiotics selects for resistance mutants not completing antibiotic prescription dose allows any resistant cells to survive and reproduce o misuses include: using outdated or weakened antibiotics using antibiotics for the common cold (virus) and other inappropriate conditions using antibiotics in animal feed failing to complete the prescribed regimen  what does antibiotic resistant bacteria mean to you? it means there will be nothing we can do for infection! bacteria resistant to ALL KNOWN antibiotics discovered if this bacteria ever spread: world-wide pandemic Vibrio vulnificus Bacterial flesh eating bacteria staph skin infection 12 hrs. after eating (raw) sushi was amputated what we are doing to address problem? removing some antibiotics from circulation…. reverse natural selection process won’t evolve toward resistance if antibiotic molecule is not there! research to discover new antibiotics molecule (natural or synthetic)  Ch.20 – Antimicrobial Drugs: Chemotherapy o What’s chemotherapy? How do microbes cause infection? o Antibiotics o Mechanisms of Antibiotics o Penicillin – the 1st antibiotic discovered o Mycobacterium – special antibiotics o Evaluating antibiotic effectiveness o Effect of antibiotic combinations o Antibiotic resistance o Antiviral drugs  anti-viral drugs 1. entry and fusion inhibitors block the receptors on the host cell that bind to the virus block fusion of the virus and cell Zika virus binding neural stem cell receptors Bacteriophage attaching to bacteria cell 2. genome integration, and nucleic acid synthesis inhibitors prevent viral uncoating inhibit viral DNA integration into the host genome nucleotide analogs inhibit RNA or DNA synthesis  Antiviral Mechanisms o Virus is NOT living – does not metabolize Antiviral approach: inhibit/disable viral proteins Cell attachment or viral enzymes example of reverse transcriptase inhibitor iExample: RNA Virus: Reverse Transcriptase Inhibitor (RTI) o Vrus with RTI include HIV and Hepatitis B Reverse transcriptase converts viral RNA to DNA RTI’s bind /inhibit reverse transcriptase  anti-viral drug example: Acyclovir Acyclovir mechanism of action for inhibition of guanine synthesis Acyclovir – nucleic acid synthesis inhibitor o similar in structure to guanine base structural similarity between Acyclovir and guanine and nucleoside incorporates into DNA instead of guanine creates “non-functional” nucleotide VIDEO: antibiotic resistance VIDEO: antibiotic resistance VIDEO: antibiotic resistance VIDEO: antibiotic resistance VIDEO: E. coli antibiotic resistance through mutation VIDEO: Ted talk – antibiotic resistance VIDEO ANNIMATION: E. coli bacteriophage reproduction animation VIDEO ANNIMATION: antibiotic resistance  Ch. 20 Learning Objectives After this lecture, you should be able to…. 9. Explan a mode of action and provide and example for anti-fungal antibiotics. Describe the challenges of using anti-fungal antibiotics. 10. Explan the mode of action and provide and example for anti-viral drugs. 11. Describe the general structure of penicillin and its mode of action against bacteria. What is the structural difference between a natural and synthetic penicillin? What is penicillinase? which penicillin is sensitive to penicillinase and why? 12. Explain why mycobacteria are highly resistant to antibiotics. Provide an antibiotic example and its mode of action against mycobacteria. 13. Describe the disk-diffusion test, e-test, and broth-dilution test and how they work to evaluate antibiotic sensitivity. 14. Compare and contrast synergism and antagonism. 15. What is antibiotic resistance? how is it happening and why is it a problem? what is MRSA? Describe three ways bacteria can obtain genes for antibiotic resistance. Explain how antibiotic resistance can be spread to other cells in the colony. 16. Describe 5 modes of action for bacterial resistance to antibiotics. 17. How are we making antibiotic resistance worse? What happens if antibiotics stop working? How are we addressing the problem? 18. Describe 4 modes of action for antiviral drugs.  Ch. 20 Learning Objectives After this lecture, you should be able to…. 1. Be familiar with terms related to chemotherapy: antimicrobial drugs, antibiotic, bactericidal, bacteriostatic and selective toxicity. 2. Describe three ways microbes damage cells and cause disease. Describe siderophore, exotoxin and endotoxin and the general differences between the two. Describe how a virus damages a cell and causes disease. 3. Describe an antibiotic; name the microbe types that produce most antibiotics; describe an antimicrobial drug. How is it that antibiotics don’t harm our cells when we use them as medication? 4. Describe potential problems of chemotherapy use for bacterial, viral, and fungal infections. 5. Define the following terms: spectrum of activity, broad-spectrum antibiotic, superinfection. 6. Explain why it is important to understand the mechanisms of action for antimicrobial drugs. What is MRSA and why is it a problem? 7. Describe the three groups of antimicrobial drugs. 8. Identify five modes of action of antibiotics. Explain why/how each mode of action is bacteria-specific. Include an antibiotic example for each mode of action.