Transcript Resistance
Mohammad Emaneini, PhD Assistant Professor in Microbiology Department of Microbiology School of Medicine Tehran University of Medical Sciences [email protected] http://tums.ac.ir/faculties/emaneini Learning Objectives Identify five modes of action of antimicrobial drugs Explain why the antibiotics are specific for bacteria List the advantages of each of the following: Semisynthetic penicillin, Cephalosporins, & Vancomycin Describe how each of the following inhibits protein synthesis: Aminoglycosides, Tetracyclines, Chloramphenicol, Macrolides Compare the mode of action of polymyxin B, bacitracin Describe how rifamycins and quinolones kill bacteria Describe how sulfa drugs inhibit microbial growth Emaneini M. PhD. The era of chemotherapy 1910 Paul Ehrlich The German chemist Discovered Salvarsan Effective against Treponema pallidum Emaneini M. PhD. The era of chemotherapy In 1928, Alexander Fleming's discovery of penicillin In 1935, Gerhard Domagk's discovery of Sulfonamidochrysoidine In 1943, Selman Waksman's discovery of streptomycin Emaneini M. PhD. The Spectrum of Antimicrobial Activity Narrow spectrum (limited spectrum) Antimicrobials effective against a (limited spectrum) of microbial types A drug effective on G+ or G- bacteria Broad spectrum (extended spectrum) Antimicrobials effective against a (extended spectrum) wide variety of microbial types A drug effective against both G+& G- bacteria Emaneini M. PhD. The Action of Antimicrobial Drugs Bactericidal Kill microbes directly Bacteriostatic Prevent microbes from growing Emaneini M. PhD. Mechanisms of Antibiotics Action Emaneini M. PhD. Mechanisms of Antibiotics Action 1- Inhibition of Cell Wall Synthesis 2- Injuring the Plasma Membrane 3- Inhibition of Protein Synthesis 4- Inhibition of Nucleic Acid Synthesis 5- Inhibiting the Synthesis of Essential Metabolites Emaneini M. PhD. Inhibition of Cell Wall Synthesis Penicillin-binding proteins (PBPs( Transpeptidases, Carboxypeptidases, Transglycosylases β-Lactam antibiotics: generally are bactericidal agents Emaneini M. PhD. Inhibition of Cell Wall Synthesis 1- Beta-Lactam Antibiotics Penicillins Cephalosporins 2- Glycopeptides Vancomycin 3- Lipopeptides Daptomycin 4- Polypeptides Bacitracin Emaneini M. PhD. Beta-Lactam Antibiotics Penicillins 6-aminopenicillanic acid Penicillium chrysogenum R β-lactam Thiazolidine Emaneini M. PhD. Natural Penicillins Penicillin G Is incompletely absorbed Inactivated by gastric acid An intravenous drug Penicillin G Penicillin V Resistant to acid Oral form Active against All β-hemolytic & most other streptococci Meningococci & most G+ anaerobes Emaneini M. PhD. Penicillin V Penicillinase resistant penicillins Nafcillin, Oxacillin, Methicillin, Cloxacillin, Dicloxacillin Similar to natural penicillins Enhanced activity against staphylococci Nafcillin Methicillin Oxacillin Dicloxacillin Cloxacillin Emaneini M. PhD. Broad-spectrum penicillins 1- Aminopenicillins: Ampicillin, Amoxicillin Ampicillin was limited primarily to Escherichia & Proteus species Amoxicillin Ampicillin 2- Carboxypenicillins: Carbenicillin, Ticarcillin Are effective against a broader range of G- bacteria Klebsiella, Enterobacter, & Pseudomonas species Ticarcillin Carbenicillin Emaneini M. PhD. Broad-spectrum penicillins 3- Ureidopenicillins: Azlocillin, Piperacillin, Mezlocillin Azlocillin Piperacillin Emaneini M. PhD. Mezlocillin Analogues Clavulanic acid, Sulbactam, Tazobactam β- lactamase inhibitors Irreversibly inactivate susceptible bacterial β- lactamases Are relatively inactive by themselves When combined with some penicillins are effective (ampicillin, amoxicillin, ticarcillin, piperacillin) Amoxicillin/clavulanic acid (Co-amoxiclav) Ampicillin/sulbactam (Sultamicillin) Clavulanic acid Sulbactam Emaneini M. PhD. Tazobactam Cephalosporins 7-aminocephalosporanic acid Originally isolated from the mold Cephalosporium Cephamycins Contain O in place of S More stable to β-lactamase hydrolysis R3 R1 β-lactam ring Dihydrothiazine ring R2 Emaneini M. PhD. First-generation (narrow-spectrum) Cefazolin, Cephalexin, Cephalothin, Cephapirin, Cephradine Escherichia coli Klebsiella species Proteus mirabilis Oxacillin-susceptible gram-positive cocci Cefazolin Cephalexin Emaneini M. PhD. Cephradine Second-generation (expanded-spectrum) Cefamandole, Cefaclor, Cefuroxime, Cefotetan, Cefoxitin Haemophilus influenzae Enterobacter species Citrobacter species Serratia species Some anaerobes, such as Bacteroides fragilis Cefoxitin Cefaclor Cefamandole Emaneini M. PhD. Third-generation (broad-spectrum) Cefixime, Cefoperazone, Cefotaxime, Ceftazidime, Ceftizoxime, Ceftriaxone Most Enterobacteriaceae Pseudomonas aeruginosa Ceftriaxone Cefixime Ceftazidime Emaneini M. PhD. Fourth-generation Cefepime, Cefpirome Activity = oxacillin against gram-positive bacteria Improved gram negative activity Cefpirome Emaneini M. PhD. Fifth-generation Ceftobiprole, Ceftaroline Ceftobiprole Ceftaroline acetate Emaneini M. PhD. Carbapenems Imipenem, Meropenem, Ertapenem Broad-spectrum antibiotics Active against virtually all organisms Resistance has been reported All oxacillin-resistant staphylococci Selected Enterobacteriaceae Pseudomonas Ertapenem Meropenem Imipenem Emaneini M. PhD. Monobactams Aztreonam Narrow-spectrum antibiotics Are active only against aerobic, G- bacteria Anaerobic bacteria and G+ bacteria are resistant Aztreonam Emaneini M. PhD. Resistant to β-lactam antibiotics 1) Prevention of the interaction of the antibiotic & the target PBP Only in G- particularly Pseudomonas species Changes in the porins Alter the size or charge of channels 2) Modification of the binding of the antibiotic to the PBP I- A mutation in the PBP gene Penicillin resistance in Enterococcus faecium II- Modification of an existing PBP through recombination Penicillin resistance in Streptococcus pneumoniae III- Acquisition of a new PBP Escherichia coli , MRSA IV- An overproduction of PBP 3) Hydrolysis of the antibiotic by β-lactamases Emaneini M. PhD. β-lactamases Serine proteases as the PBPs > 200 different β-lactamases Penicillinases: specific for penicillins Cephalosporinases: specific for cephalosporins Carbapenemases: specific for carbapenems Four classes (A to D) Emaneini M. PhD. β-lactamases Class A The most common are SHV-l & TEM-l Found in G- rods (e.g., Escherichia, Klebsiella) Minimal activity against cephalosporins Point mutations: Extended-spectrum β-lactamases [ESBLs] Are commonly encoded on plasmids Emaneini M. PhD. β-lactamases Class B Zinc dependent metalloenzymes Broad spectrum of activity against all β-lactam antibiotics Class C Are primarily cephalosporinases Are encoded on the bacterial chromosome Class D Are penicillinases Found primarily in G- rods Emaneini M. PhD. Glycopeptides: Vancomycin Obtained from Streptomyces orientalis Interacts with the D-alanine-D-alanine in the pentapeptide Is inactive against G- bacteria Intrinsically resistant D-alanine-D-lactate Lactobacillus, Erysipelothrix D-alanine-D-serine Enterococcus gallinarum, E. casseliflavus Acquired resistance: vanA & vanB Emaneini M. PhD. Vancomycin Polypeptides: Bacitracin Bacillus licheniformis Interfering with dephosphorylation of the lipid carrier Damage cytoplasmic membrane and inhibit RNA transcription The treatment of skin infections caused by Staphylococcus & group A Streptococcus Used in creams, ointments, sprays G- bacteria are resistant Resistance: failure of the antibiotic to penetrate into the cell Bacitracin Emaneini M. PhD. Inhibition of Cell Wall Synthesis Isoniazid, Ethionamide, Ethambutol, & Cycloserine Used for the treatment of mycobacterial infections Isoniazid Isonicotinic acid hydrazide [INH]) Bactericidal; Blocks mycolic acid synthesis Ethionamide Derivative of INH Blocks mycolic acid synthesis Ethambutol Interferes with the synthesis of arabinogalactan in the cell wall Cycloserine Inhibits D-alanine-Dalanine synthetase & Alanine racemase Emaneini M. PhD. Injuring the Plasma Membrane 1- Lipopeptides Daptomycin 2- Polypeptides Polymyxins Emaneini M. PhD. Lipopeptides: Daptomycin A naturally cyclic lipopeptide Streptomyces roseosporus Binds irreversibly to the CM. Disruption of the ionic gradients Active against G+ bacteria G- bacteria are resistant Emaneini M. PhD. Daptomycin Polypeptides: Polymyxins Cyclic polypeptides Bacillus polymyxa Interacting with LPS & the phospholipids in the OM Increased cell permeability Polymyxin B & E (Colistin) causing serious nephrotoxicity Localized infections: external otitis, eye & skin infections Colistin Polymyxin B Emaneini M. PhD. Inhibition of Protein Synthesis Emaneini M. PhD. Inhibition of Protein Synthesis Emaneini M. PhD. Aminoglycosides Amino sugars --- Glycosidic Bond--- Aminocyclitol ring Bactericidal Bind irreversibly to ribosomal proteins Misreading of the messenger RNA (mRNA) Premature release of the ribosome from mRNA Streptomycin, Neomycin, Kanamycin, & Tobramycin Streptomyces species Gentamicin & Sisomicin Micromonospora species Amikacin from kanamycin Netilmicin from sisomicin Systemic infections caused by many G- rods Emaneini M. PhD. Streptomycin Aminoglycosides Resistance 1- Mutation of the ribosomal binding site 2- Decreased uptake of the antibiotic (Anaerobic bacteria) 3- Increased expulsion of the antibiotic from the cell 4- Enzymatic modification The most common mechanism of resistance Phosphotransferases (APHs; 7 described) Adenyltransferases (ANTs; 4 described) Acetyltransferases (AACs; 4 described) Emaneini M. PhD. Tetracyclines Broad-spectrum Bacteriostatic Tetracycline, Doxycycline, Minocycline Binding reversibly to the 30S Blocking the binding of aminoacyl-tRNA Chlamydia, Mycoplasma, Rickettsia Emaneini M. PhD. The staining of teeth associated with tetracycline use Tetracyclines Resistance 1- Decreased penetration of the antibiotic 2- Active efflux of the antibiotic out of the cell 3- Alteration of the ribosomal target site 4- Enzymatic modification of the antibiotic Emaneini M. PhD. Glycylcycline Tigecycline Semisynthetic derivative of minocycline Inhibits protein synthesis as the tetracyclines Broad spectrum of activity: G+, G- & anaerobic bacteria Resistant Bacteria Proteus Morganella Providencia Pseudomonas aeruginosa Emaneini M. PhD. Oxazolidinones Linezolid Narrow-spectrum Block initiation of protein synthesis (70S initiation complex) Binds to the 50S ribosomal subunit Mechanism of resistance Target site modification Emaneini M. PhD. Chloramphenicol Broad spectrum Bacteriostatic Blocking peptide elongation Binding reversibly to the peptidyl transferase (50S) Only for the treatment of typhoid fever Can produce aplastic anemia (1 per 24,000 treated patients) Resistance: plasmid-encoded chloramphenicol acetyltransferase Emaneini M. PhD. Macrolides Erythromycin, Azithromycin, Clarithromycin Streptomyces erythreus Desosamine Broad spectrum Bacteriostatic Blocks polypeptide elongation Reversible binding to the 23S rRNA Used to treat pulmonary infections Mycoplasma, Legionella, & Chlamydia species Infections caused by Campylobacter species Emaneini M. PhD. Cladinose Macrolides Resistance 1- Alteration of the ribosomal target site Methylation of the 23S rRNA 2- Enzymatic modification of the antibiotic Destruction of the lactone ring by an erythromycin esterase 3- Mutations in the 23S rRNA & ribosomal proteins Emaneini M. PhD. Ketolides Telithromycin Semisynthetic derivatives of erythromycin Increase stability in acid Blocks protein synthesis as Macrolides Broad-spectrum antibiotic Active against some macrolide resistant staphylococci & enterococci Emaneini M. PhD. Lincosamide Clindamycin Derivative of lincomycin (Streptomyces lincolnensi) Inhibits peptidyl transferase Block the binding of the amino acid-acyltRNA complex Resistance: Methylation of the 23S ribosomal RNA E CD حساس E CD E CD مقاومت پيوسته مقاومت القايي Emaneini M. PhD. Streptogramin Streptogramin Cyclic peptides Streptomyces species Group A and group B Quinupristin-dalfopristin (Synercid) Dalfopristin prevents peptide chain elongation Quinupristin initiates premature release of peptide Emaneini M. PhD. Inhibition of Nucleic Acid Synthesis 1- Quinolones 2- Rifampin 3- Metronidazole Emaneini M. PhD. Quinolones Synthetic Inhibit bacterial DNA gyrases (II) or topoisomerases (IV) Nalidixic acid Fluoroquinolones: Ciprofloxacin Levofloxacin Gatifloxacin Resistance: mutations in chromosomal genes of DNA gyrases (II) or topoisomerases (IV) Emaneini M. PhD. Rifampin Semisynthetic derivative of rifamycin B Streptomyces mediterranei Inhibits the initiation of RNA synthesis Bactericidal Mycobacterium tuberculosis Staphylococci Streptococci Resistance: a mutation in the chromosomal gene that codes for the β subunit of RNA polymerase (In G+) Emaneini M. PhD. Metronidazole Reduction of its nitro group by bacterial nitroreductase Producing cytotoxic compounds that disrupt the host DNA Anaerobic bacterial infections (B. fragilis) Resistance 1- Decreased uptake 2- Elimination of the cytotoxic compounds Emaneini M. PhD. Antimetabolites Sulfonamides Preventing the synthesis of the folic acid Compete with p-aminobenzoic acid Mammalian organisms do not synthesize folic acid Treatment of Nocardia, Chlamydia, & some protozoa infections Sulfacetamide R Group Emaneini M. PhD. Sulfadiazine Sulfisoxazole Antimetabolites Trimethoprim Blocks the conversion of dihydrofolate to tetrahydrofolate Inhibiting dihydrofolate reductase Trimethoprim + sulfamethoxazole: Synergistic combination Treatment of acute and chronic urinary tract infections Resistance Permeability barriers : Pseudomonas Decreased affinity of dihydrofolate reductase Emaneini M. PhD. Mechanisms of Resistance 1- Enzymatic Destruction or Inactivation of the Drug 2- Prevention of Penetration to the Target Site 3- Alteration of the Drug's Target Site 4- Rapid Efflux (Ejection) of the Antibiotic Emaneini M. PhD. Antibiotic Assays The disk agar diffusion (DAD) method involves Different antibiotics diffusing from paper disks in a bacterial colony Emaneini M. PhD. Antibiotic Assays The tube dilution method determines the minimum inhibitory concentration (MIC) Emaneini M. PhD. Emaneini M. PhD.