Unit 3. section 2(1)(1).pptx

Unit 3. Control of Microorganisms Section 2: Antimicrobial drugs ( chapter 14) Note: Skip 14.4, 14.7 14.1 History of Chemotherapy and Antimicrobial Discovery Ancient Societies • Chemical analyses of people from present day Sudan around 350 to 550AD reveal evidence of tetracycline infused beer us...

Unit 3. Control of Microorganisms Section 2: Antimicrobial drugs ( chapter 14) Note: Skip 14.4, 14.7 14.1 History of Chemotherapy and Antimicrobial Discovery Ancient Societies • Chemical analyses of people from present day Sudan around 350 to 550AD reveal evidence of tetracycline infused beer used to treat ailments like gum disease and wounds. • Healers, herbalists around the world have recognized antimicrobial properties of plants and fungi. Figure 14.2 • For millennia, Chinese herbalists have used many different species of plants for the treatment of a wide variety of human ailments. The First Antimicrobial drugs • 1910- Paul Ehrlich• synthesized first chemical that kills pathogens Arsphenamine( Salvarsan) • Compound 606 targeted syphilis Figure 14.3 The First Antimicrobial Drugs • 1935- Josef Klarer, Fritz Mietzsch, and Gerhard Domagk • Discovered prontosil, synthetic chemical dye • First commercially available antibiotic • treated daughter, who had become infected with septicemia • Effective in treating Streptococcus and Staphylococcus infections • Sulfanilamide is the active breakdown product of prontosil in the body. • the first synthetic antimicrobial created • served as the foundation for the chemical development of a family of sulfa drugs. The first antimicrobial Drugs 1929- Alexander Fleming – Noticed no bacteria growing on green mold Found the fungus Penicillium produces penicillin developed assay for isolation penicillin/ did not isolate penicillin • Penicillin is known as first natural antibiotic • • • • • 1940- Florey and Chain isolate penicillin and show it was effective against a variety of diseases: gonorrhea, meningitis • Drug becomes available for commercial use Figure 14.4 (a) Alexander Fleming was the first to discover a naturally produced antimicrobial, penicillin, in 1928. (b) Howard Florey and Ernst Chain discovered how to scale up penicillin production. Then they figured out how to purify it and showed its efficacy as an antimicrobial in animal and human trials in the early 1940s. Photograph of Fleming’s culture plate. © National Library of Medicine The first Antimicrobial Drugs • Albert Schatz, E. Bugie, and Selman Waksman • 1944 Examined soil and isolated actinomycin, streptomycin (soon to be used against tuberculosis), and neomycin • Coined term “antibiotic” • Waksman is awarded the Nobel Prize in Medicine or Physiology in 1952. Synthetic drugs vs antibiotics • Synthetic drugs- drugs that are made in the lab: Salvarsan and prontosil • Antibiotics-agents that work to kill or inhibit living organisms • Semi-synthetic-A natural antibiotic that has been chemically modified in the laboratory to enhance its efficiency: increase the range of bacteria targeted, increase stability, decrease toxicity, or confer other properties beneficial for treating infections. 14.2 Fundamentals of Antimicrobial Chemotherapy Bacteriostatic versus bactericidal antibacterial drugs • Bacteriostatic drugs cause a reversible inhibition of growth, with bacterial growth restarting after elimination of the drug. • Bactericidal drugs kill their target bacteria. • Essential for immunocompromised or life-threatening infections Spectrum of Activity • antimicrobial spectrumrange of microbial action • Types • Narrow-affects single microbial group • Ex: Penicillin • Broad-effective against more than one bacterial group • Use when not sure of source • Misuse can lead to superinfections as will also target normal microbiota • Ex: Ampicillin Development of Superinfection • Broad-spectrum antimicrobial use may lead to the development of a superinfection. (credit: modification of work by Centers for Disease Control and Prevention) Figure 14.6 Dosage and Route of Administration • Dosage • The amount of medication given during a certain time interval Dosage and Route of Administration • Route of Administration • the method used to introduce a drug into the body • Oral, topical, parenteral (intravenous or intramuscular) Dosage and Route of Administration • Selective toxicity -antimicrobial drug should harm the infectious agent but not the host. • Toxic dose- concentration of the drug causing harm to the host. • Therapeutic dose- concentration of the drug that effectively destroys or eliminates the pathogen from the host. • Chemotherapeutic index- the highest concentration of the drug tolerated by the host divided by the lowest concentration of the drug that will eliminate the infection or disease agent A Representation of the Chemotherapeutic Index. 14.3 Mechanisms of Antibacterial Drugs Mode of action • definition-the way in which a drug affects microbes at the cellular level • Common targets of antibacterial drugs • Cell wall-peptidoglycan • Protein synthesis( Ribosomes) - targets 70S ribosome • Plasma membrane- permeability • Nucleic acid synthesis- replication/transcription • metabolic pathways – PABA ( folic acid synthesis) Figure 14.9 • There are several classes of antibacterial compounds that are typically classified based on their bacterial target. Inhibitors of Cell Wall Biosynthesis • One of most common mechanisms of action for antibiotics is blocking synthesis of bacterial cell wall • Mostly targets peptidoglycan • Only affects bacterial cell wall Inhibitors of Cell Wall Biosynthesis Cell wall synthesis penicillins cephalosporins Monobactams Carbapenems Vancomycin Bacitracin Inhibitors of Cell Wall Biosynthesis: Beta lactams • Beta lactams• Most widely used antibiotics • inhibit cell wall biosynthesis • block the crosslinking of peptide chains during the biosynthesis of new peptidoglycan in the bacterial cell wall Inhibitors of Cell Wall Biosynthesis: Beta lactams • Penicillin • Mode of action: inhibits peptide cross linking of carbohydrates between peptidoglycan layers during cell wall formation. • Spectrum: mostly narrow: • antibiotics G+, including staph, streptococci, clostridia, pneumococci • Semisynthetics G+ plus some G-, including gonorrhea, meningitis, syphilis causing bacteria • Examples: • Penicillin G • Ampicillin Inhibitors of Cell Wall Biosynthesis: Beta lactams Some Members of the Penicillin Group of Antibiotics. Inhibitors of Cell Wall Biosynthesis: Beta lactams The Action of Penicillinase on Sodium Penicillin G. Inhibitors of Cell Wall Biosynthesis: Beta lactams • Cephalosporins • Mode of action: • Inhibits peptidoglycan synthesis • Spectrum: Antibiotics control mostly G+ • Semisynthesis inhibit some G- • Isolated from Cephalosporium acremonium-cephalosporin C • Used as alternatives to penicillin where resistance is encountered • As have increased resistance to enzymatic inactivation by Blactamases • Examples: • Cefaclor, cefadroxil, cefazolin Inhibitors of Cell Wall Biosynthesis: Beta lactams • Monobactams • Mode of action: inhibits cell wall biosynthesis • Spectrum: narrow, active against aerobic, G- rods, especially those in nosocomial diseases and bacterial meningitis • Isolated from Chromobacter violaceum • Examples: Aztreonam Inhibitors of Cell Wall Biosynthesis: Beta lactams • Carbapenems • Mode of action: • Spectrum: broadest spectrum of B lactams, aerobic G+, G- and some anaerobes • originally developed from thienamycin, a naturallyderived product of Streptomyces cattleya • Examples: • Imipenem, Meropenem, Doripenem Figure 14.10 • Penicillins, cephalosporins, monobactams, and carbapenems all contain a β-lactam ring, the site of attack by inactivating β-lactamase enzymes. Although they all share the same nucleus, various penicillins differ from each other in the structure of their R groups. Chemical changes to the R groups provided increased spectrum of activity, acid stability, and resistance to β-lactamase degradation. Inhibitors of Cell Wall Biosynthesis: vancomycin • Vancomycin • Mode of action: inhibits cell wall biosynthesis, but on different fragment of cell wall when compared to penicillins and cephalosporins: disrupts NAM-NAG backbone • Spectrum: narrow, G+ • Very large, complex molecule • Used for severe staph diseases, Clostridium, enterococcus, where resistance has developed or penicillin allergy exists • Isolated from Amycolaptosis orientalis Inhibitors of Cell Wall Biosynthesis: Bacitracin • Bacitracin • Mode of action: interferes with transport of cell wall precursors through cell membrane • Spectrum: broad, G+ and G• Available as skin ointment against G+ induced skin infections • Examples: • Neosporin- when combined with neomycin and polymyxin B Inhibitors of Protein Synthesis • Protein synthesis relies on differences between bacterial and eukaryotic synthetic machinery • Eukaryotes: 80S ribosomes • Prokaryotes: 70S ribosomes(50S +30S) • Affects 70S ribosomes: will bind to either small(30S) or large(50S) subunit • Inhibit formation peptide bonds in growing polypeptide chain • Most broad spectrum Protein Synthesis Ribosomes 50 30 Protein synthesis aminoglycosides tetracycline macrolides chloramphenicol Figure 14.11 • The major classes of protein synthesis inhibitors target the 30S or 50S subunits of cytoplasmic ribosomes. Inhibitors of Protein Synthesis: 30S • Aminoglycosides • Mode of action: binds to 30S ribosomal subunit(blocking the reading of the genetic code on mRNA) and inhibit protein synthesis • Spectrum: Broad • Large, highly polar • Must be administered by intramuscular injection • Examples: • Streptomycin, Gentamicin, Neomycin, Kanamycin Inhibitors of Protein Synthesis: 30S • Tetracyclines • Mode of action: Bind to 30S ribosome, inhibiting recognition of aminoacyl tRNA • Spectrum: Broad: G-, G+, chlamydia, rickettsia, mycoplasma • Drugs of choice for rickettsial and chlamydial diseases • Examples: • Chlortetracycline, Minocycline, doxycycline • Glycylcyclines-related to tetracyclines: tygecycline Inhibitors of Protein Synthesis: 50S • Macrolides • Mode of action: block protein synthesis by inhibiting chain elongation • Spectrum:G+ cocci and intracellular pathogens such as Mycoplasma, chlamydia, Campylobacter, Legionella • Large, complex ring structure • Example: Erythromycin, Chlarithromycin(Biaxin), Azithromycin(Zithromax), Telithromycin Inhibitors of Protein Synthesis: 50S • Lincosamide • Mode of action: bind to 50S subunit and inhibit chain elongation • Spectrum: narrow, G+ cocci, nonspore forming anaerobic • Particularly active against streptococcal and staph infections • Example: • Lincomycin, clindamycin Inhibitors of Protein Synthesis: 50S • Chloramphenicol • Mode of action: binds to 50S ribosome subunit (inhibits peptide bond formation) • Spectrum: broad: G-, G+, chlamydia, rickettsia, mycoplasma, and fungi • Isolated from Streptomyces venezualae • first antibacterial drug synthetically mass produced • Drug of choice for endemic cholera, epidemic typhus, and Rocky mountain spotted fever Inhibitors of Protein Synthesis: both • Oxazolidinones • Mode of action: interfere chain initiation by 50S and 30S subunit • Spectrum: narrow: G+ • Last resort: Toxic to mitochondria, can produce allergic reactions Inhibitors of membrane function • Antibiotic, especially polypeptide, brings about changes in permeability of plasma membrane • Loss of important metabolites for bacteria Cell membrane Cell membrane polymyxins daptomycin Inhibitors of membrane function • Polymyxin (polypeptide) • Mode of action: similar to detergents in that affect the cell’s permeability and cause loss of cytoplasmic constituents; interact with LPS layer • Spectrum: most active against G-, like Pseudomonas, and those causing those superficial infections in wounds, abrasions, and burns. Examples: Polymyxin B • Polysporin- bacitracin, polymyxin B, gramicidin • Neosporin- bacitracin, polymyxin B, neomycin Polymycin E (colistin)- last resort, intravenously for serious infections Inhibitors of membrane function • daptomycin • Mode of action: Inserts in the bacterial cell membrane and disrupts it. • Spectrum: Active against G+ • Cyclic lipopeptide • produced by Streptomyces roseosporus • It is typically administered intravenously and seems to be well tolerated, showing reversible toxicity in skeletal muscles. Inhibitors of nucleic acid synthesis • Interferes with process of DNA replication and transcription in microorganisms Nucleic acids Nucleic acids rifampin quinolones DNA mRNA Inhibitors of nucleic acid synthesis • Rifampin • Mode of action: Binds to RNA polymerase, interrupting transcription • Spectrum: Narrow, Mycobacteria, G+ cocci • Semisynthetic member of rifamycin family • Isolated from Streptomyces mediterranei • Primarily used against tuberculosis Inhibitors of nucleic acid synthesis • Quinolones • Mode of action: bind to DNA gyrase (topoisomerase II) and inhibits DNA synthesis • Spectrum of action: broad: G+, G-, mycoplasmas, mycobacteria • Synthetic antibacterial drugs • Example: Nalidixic acid • Derivatives called fluoroquinolones are used to treat urinary tract infections, gonorrhea, chlamydia, intestinal tract infections. • Example: ciprofloxacin(Cipro), levofloxacin • are among the most commonly prescribed antibiotics used to treat a wide range of infections, including urinary tract infections, respiratory infections, abdominal infections, and skin infections. Inhibitors of Metabolic pathways • Some synthetic drugs control bacterial infections by functioning as antimetabolites, competitive inhibitors for bacterial metabolic enzymes Folic acid synthesis • Folic acid normally synthesized by bacteria and important in nucleic acid synthesis • In order to make folic acid, Pteridine, glutamic acid, and PABA must combine. • Subsequently, folic acid is converted to dihydrofolic acid (DHF) and finally tetrahydrofolic acid (THF) • This last step is necessary for folic acid to be active • Tetrahydrofolic acid is a precursor of thymidine • Since humans don’t produce folic acid, but instead get from food, antibacterials that inhibit folic acid synthesis do not harm human host Folic acid synthesis Folic acid metabolism sulfonamides trimethoprim PABA p-aminobenzoic acid THF DHF Inhibitors of metabolic pathways • Sulfonamides(sulfa drugs) • Mode of action: inhibits folic acid synthesis • Spectrum: broad: G+, G-, chlamydia but now many resistant • Synthetic antimicrobial drugs • Examples: • Sulfanilamide • Para-aminobenzoic acid(PABA) needed to make folic acid • Sulfanilamide competes with PABA for active site in bacterial enzyme, preventing the formation of folic acid, resulting in the stoppage of nucleic acid synthesis and DNA replication • Trimethoprim • Competes with dihydrofolic acid for active site in bacterial enzyme, preventing the formation of tetrahydrofolic acid, which results in stoppage of nucleic acid synthesis and DNA replication • Sulfamethoxazole • Used in combination with trimethoprim to treat urinary tract infections, ear infections, and bronchitis. The Disruption of Folic Acid Synthesis by Competitive Inhibition. Figure 14.12 • Sulfonamides and trimethoprim are examples of antimetabolites that interfere in the bacterial synthesis of folic acid by blocking purine and pyrimidine biosynthesis, thus inhibiting bacterial growth. Inhibition of metabolic pathways • Isoniazid• Mode of action: inhibits mycolic acid synthesis • Spectrum: narrow: Mycobacteria • Synthetic antimicrobial drug • Used in combination with rifampin or streptomycin in treatment of tuberculosis Modes of action Cell wall synthesis penicillins cephalosporins monobactams carbapenems vancomycin bacitracin Nucleic acids replication rifampin quinolones DNA THF Folic acid metabolism sulfonamides trimethoprim mRNA DHF Ribosomes PABA Cell membrane polymyxins daptomycin 50 30 Protein synthesis aminoglycosides tetracycline macrolides lincosamides chloramphenicol oxazolidinones 14.5 Drug Resistance Resistance • Natural : microorganism never sensitive to drug • Acquired: microorganism initially sensitive to drug now grows due to genetic changes: horizontal gene transfer and mutations Resistance can be coded in chromosome or R plasmids Resistance mechanisms Beta Lactam Porin PBP Cell wall synthesis Lysis PBP: penicillin binding protein Drug Modification or Inactivation Antibiotic modification: enzymes that inactivate the antibiotic Porin PBP Cell wall synthesis Examples: E. Coli Pseudomonas Prevention of cellular uptake or efflux Porin PBP Cell wall synthesis Less drug enters the cell pump Porin PBP Cell wall synthesis Drug is pumped out of the cell Examples: Streptococcus pneumonie MRSA Target Modification Antibiotic binding site • providing resistance to B- lactams DNA gyrase • providing resistance to fluoroquinolones metabolic enzymes • providing resistance to sulfa drugs, sulfones, and trimethoprim; and peptidoglycan subunit peptide chains • providing resistance to glycopeptides. Porin PBP Cell wall synthesis Altered binding site/metabolic pathway ribosome subunits • providing resistance to macrolides, tetracyclines, and aminoglycosides lipopolysaccharide (LPS) structure • providing resistance to polymyxins RNA polymerase • providing resistance to rifampin Multiple resistance pump Porin PBP Cell wall synthesis Figure 14.18 • There are multiple strategies that microbes use to develop resistance to antimicrobial drugs. (Not shown: target overproduction, target mimicry, and enzymatic bypass). (credit: modification of work by Gerard D Wright) 14.6 Testing the effectiveness of antimicrobials Kirby-Bauer Disk Diffusion test • several antibiotic paper disks placed on Mueller-Hilton agar plate inoculated with bacteria Dilution Tests • MIC- minimum inhibitory concentration • The lowest concentration that will inhibit the visible growth of a microorganism • MBC- minimum bacteriocidal concentration • The minimum concentration that kills 99.9% cells of a given bacterial strain Dilution Tests • tube dilution test- inoculate tubes containing different dilutions of antibiotics with identical number of bacteria Figure 14.19 tube dilution test • In a dilution test, the lowest dilution that inhibits turbidity (cloudiness) is the MIC. In this example, the MIC is 8 μg/mL. Broth from samples without turbidity can be inoculated onto plates lacking the antimicrobial drug. The lowest dilution that kills ≥99.9% of the starting inoculum is observed on the plates is the MBC. (credit: modification of work by Suzanne Wakim) Figure 14.20 • Microdilution tray A microdilution tray can also be used to determine MICs of multiple antimicrobial drugs in a single assay. In this example, the drug concentrations increase from left to right and the rows with clindamycin, penicillin, and erythromycin have been indicated to the left of the plate. For penicillin and erythromycin, the lowest concentrations that inhibited visible growth are indicated by red circles and were 0.06 μg/mL for penicillin and 8 μg/mL for erythromycin. For clindamycin, visible bacterial growth was observed at every concentration up to 32 μg/mL and the MIC is interpreted as >32 μg/mL. (credit: modification of work by Centers for Disease Control and Prevention) Figure 14.21 E test • The Etest can be used to determine the MIC of an antibiotic. • A paper strip impregnated with marked gradient of antibiotic is placed on the plate • In this Etest, vancomycin is shown to have a MIC of 1.5 μg/mL against Staphylococcus aureus.