Antibiotics,Step 1: How to Kill a Bacterium.,What are the bacterial weak points? Specifically, which commercial antibiotics target each of these points?,Target 1: The Bacterial Cell Envelope,Two types of bacteria,Gram-positive: Stained dark blue by Gram-staining procedureGram-negative: Dont take up the crystal violet stain, and take up counterstain (safranin) instead, staining pink in the Gram procedure.,Structure of the bacterial cell envelope. Gram-positive. Gram-negative.,Gram staining animation,http:/student.ccbcmd.edu/courses/bio141/labmanua/lab6/images/gram_stain_11.swf,Structure of peptidoglycan. Peptidoglycan synthesis requires cross-linking of disaccharide polymers by penicillin-binding proteins (PBPs). NAMA, N-acetyl-muramic acid; NAGA, N-acetyl-glucosamine.,Antibiotics that Target the Bacterial Cell Envelope Include:,The b-Lactam Antibiotics Vancomycin Daptomycin,Target 2: The Bacterial Process of Protein Production,An overview of the process by which proteins are produced within bacteria.,Structure of the bacterial ribosome.,Antibiotics that Block Bacterial Protein Production Include:,Rifamycins Aminoglycosides Macrolides and Ketolides Tetracyclines and Glycylcyclines Chloramphenicol Clindamycin Streptogramins Linezolid (member of Oxazolidinone Class),Target 3: DNA and Bacterial Replication,Bacterial synthesis of tetrahydrofolate.,Supercoiling of the double helical structure of DNA. Twisting of DNA results in formation of supercoils. During transcription, the movement of RNA polymerase along the chromosome results in the accumulation of positive supercoils ahead of the enzyme and negative supercoils behind it. (Adapted with permission from Alberts B, Johnson A, Lewis J, et al. Molecular Biology of the Cell. New York: Garland Science, 2002:314.),Replication of the bacterial chromosome. A consequence of the circular nature of the bacterial chromosome is that replicated chromosomes are interlinked, requiring topoisomerase for appropriate segregation.,Antibiotics that Target DNA and Replication Include:,Sulfa Drugs Quinolones Metronidazole,Which Bacteria are Clinically Important?,Gram-positive aerobic bacteria Gram-negative aerobic bacteria Anaerobic bacteria (both Gram + and -) Atypical bacteria Spirochetes Mycobacteria,General Classes of Clinically Important Bacteria Include:,Gram-positive Bacteria of Clinical Importance,Staphylococci Staphylococcus aureus Staphylococcus epidermidis Streptococci Streptococcus pneumoniae Streptococcus pyogenes Streptococcus agalactiae Streptococcus viridans Enterococci Enterococcus faecalis Enterococcus faecium Listeria monocytogenes Bacillus anthracis,Staphylococcus aureus,Streptococcus viridans,Gram-negative Bacteria of Clinical Importance,Enterobacteriaceae Escherichia coli, Enterobacter, Klebsiella, Proteus, Salmonella, Shigella, Yersinia, etc. Pseudomonas aeruginosa Neisseria Neisseria meningitidis and Neisseria gonorrhoeae Curved Gram-negative Bacilli Campylobacter jejuni, Helicobacter pylori, and Vibrio cholerae Haemophilus Influenzae Bordetella Pertussis Moraxella Catarrhalis Acinetobacter baumannii,Anaerobic Bacteria of Clinical Importance,Gram-positive anaerobic bacilli Clostridium difficile Clostridium tetani Clostridium botulinum Gram-negative anaerobic bacilli Bacteroides fragilis,Atypical Bacteria of Clinical Importance Include:,Chlamydia Mycoplasma Legionella Brucella Francisella tularensis Rickettsia,Spirochetes of Clinical Importance Include:,Treponema pallidumBorrelia burgdorferiLeptospira interrogans,Mycobacteria of Clinical Importance Include:,Mycobacterium tuberculosis Mycobacterium avium Mycobacterium leprae,Antibiotics that Target the Bacterial Cell Envelope,The b-Lactam Antibiotics,Mechanism of action of -lactam antibiotics. Normally, a new subunit of N-acetylmuramic acid (NAMA) and N-acetylglucosamine (NAGA) disaccharide with an attached peptide side chain is linked to an existing peptidoglycan polymer. This may occur by covalent attachment of a glycine () bridge from one peptide side chain to another through the enzymatic action of a penicillin-binding protein (PBP). In the presence of a -lactam antibiotic, this process is disrupted. The -lactam antibiotic binds the PBP and prevents it from cross-linking the glycine bridge to the peptide side chain, thus blocking incorporation of the disaccharide subunit into the existing peptidoglycan polymer.,Mechanism of penicillin-binding protein (PBP) inhibition by -lactam antibiotics. PBPs recognize and catalyze the peptide bond between two alanine subunits of the peptidoglycan peptide side chain. The -lactam ring mimics this peptide bond. Thus, the PBPs attempt to catalyze the -lactam ring, resulting in inactivation of the PBPs.,Six Ps by which the action of -lactams may be blocked: penetration, porins, pumps, penicillinases (-lactamases), penicillin-binding proteins (PBPs), and peptidoglycan.,The Penicillins,INTRODUCTION,Antibacterial agents which inhibit bacterial cell wall synthesis Discovered by Fleming from a fungal colony (1928) Shown to be non toxic and antibacterial Isolated and purified by Florey and Chain (1938) First successful clinical trial (1941) Produced by large scale fermentation (1944) Structure established by X-Ray crystallography (1945) Full synthesis developed by Sheehan (1957) Isolation of 6-APA by Beecham (1958-60) - development of semi-synthetic penicillins Discovery of clavulanic acid and b-lactamase inhibitors,