Antibiotic Resistance The Miracle Revoked? Wilson “Bill” Muse 10/29/2009

Eukaryotes Fungi Azoles Allylamines Cycloheximide Polyenes Polyoxins Nucleic acid analogs Echinocandins Bacteria Mycobacteria Gram-negative Bacteria Gram-positive Bacteria Obligately parasitic Bacteria Chlamydia Rickettsia Viruses RNA viruses DNA viruses Tobramycin Penicillins Streptomycin Sulfonamides Cephalosporins Quinolones Isoniazid Tetracycline Vancomycin Daptomycin Platensimycin Polymyxins Nucleoside analogs Interferon Nonnucleoside reverse-transcriptase inhibitors Protease inhibitors Fusion inhibitors The Miracle of Antibiotics

Classes of antibiotics Aminoglycosides Tetracyclines Sulfonamides Quinolones Polypeptides B-lactams Macrolides Glycopeptides Cephalosporins

Antibiotic modes of action 5 main targets Prevent cell wall synthesis (B-lactams) Disrupt membrane function (polymyxins) Prevent protein synthesis (chloramphenicols) Prevent nucleic acid synthesis (quinolones) Disrupt metabolic pathways (sulfanilamides)

Cell wall synthesis Cycloserine Vancomycin Bacitracin Penicillins Cephalosporins Monobactams Carbapenems Folic acid metabolism Quinolones Nalidixic acid DNA gyrase Ciprofloxacin Novobiocin Trimethroprim Sulfonamides DNA THF DHF mRNA Ribosomes Cytoplasmic membrane structure and function Polymyxins Daptomycin PABA Cytoplasmic membrane Cell wall Plantensimycin Lipid biosynthesis Protein synthesis (tRNA) Mupirocin Puromycin Tetracyclines Spectinomycin Streptomycin Gentamicin Kanamycin Amikacin Nitrofurans Lincomycin Protein synthesis (30S inhibitors) Erythromycin (macrolides) Chloramphenicol Clindamycin Rifampin Streptovaricins DNA-directed RNA polymeraseRNA elongation Actinomycin Protein synthesis (50S inhibitors)

Antibiotics: Mechanisms of Action Inhibition of Cell Wall Synthesis -some antibiotics prevent peptidoglycan formation Examples: vancomycin, amoxicillin, ampicillin, penicillin

Cross-linking of peptidoglycan transpeptidase

CNHCH C O OCN CH 3 COOH S STRUCTURE OF PENICILLIN

Antibiotics: Mechanisms of Action Inhibition of Bacterial Protein Synthesis - some antibiotics bind to the large or small subunit of the bacterial ribosome Examples: neomycin, streptomycin, azithromycin, erythromycin, tetracycline

Binding and altering ribosome structure Aminoglycosides neomycin

Mechanism of Action Once inside the cell… –Bind 30S ribosomal subunit –Blocks binding of aminoacyl-tRNA to acceptor site on mRNA-ribosome complex –Protein synthesis is inhibited = bacteriostatic effect

Summary of Targets

How Antibiotic Resistance Happens

Overcoming the arsenal Modify antibiotic Pump it out Alter the target site Bypass the pathway

CNHCH C O OCN CH 3 COOH S Site of penicillinase action. Breakage of the B-lactam ring. Alter the drug to render ineffective

ex: anti-streptomycin ex. anti-sulfanilamides ex: anti-B-lactams ex: anti-tetracyclins quinolines

Mechanisms of antibiotic resistance Efflux Pumps Hydrolysis Reduced Uptake Sequestering Enzymatic Modification

mechanisms The four main mechanisms by which microorganisms exhibit resistance to antimicrobials are: Drug inactivation or modification: e.g. enzymatic deactivation of Penicillin G in some penicillin-resistant bacteria through the production of ß-lactamases. Alteration of target site: e.g. alteration of PBP—the binding target site of penicillins— in MRSA and other penicillin-resistant bacteria. Alteration of metabolic pathway: e.g. some sulfonamide-resistant bacteria do not require para-aminobenzoic acid (PABA), an important precursor for the synthesis of folic acid and nucleic acids in bacteria inhibited by sulfonamides. Instead, like mammalian cells, they turn to utilizing preformed folic acid. Reduced drug accumulation: by decreasing drug permeability and/or increasing active efflux (pumping out) of the drugs across the cell surface.[4] There are three known mechanisms of fluoroquinolone resistance. Some types of efflux pumps can act to decrease intracellular quinolone concentration. In gram-negative bacteria, plasmid-mediated resistance genes produce proteins that can bind to DNA gyrase, protecting it from the action of quinolones. Finally, mutations at key sites in DNA gyrase or Topoisomerase IV can decrease their binding affinity to quinolones, decreasing the drug's effectiveness.[5]

Tetracyclines Broad-spectrum activity –Includes aerobic G+ and G-, atypicals [Rickettsia spp, treponema spp, chlamydia spp, and others] –Little to no effect on fungi or viruses Tetracycline Doxycycline* Minocycline Tigecycline

Summary Bacteria have evolved ways to counteract the effects of most antibiotics. They mutate to alter target sites or recruit enzymes to degrade or pump out antibiotics They share their tricks with other bacteria through gene transfer