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

Structure of the bacterial cell envelope. Gram-positive. Gram-negative.

Structure of peptidoglycan 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 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 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?

General Classes of Clinically Important Bacteria Include: Gram-positive aerobic bacteria Gram-negative aerobic bacteria Anaerobic bacteria (both Gram + and -) Atypical bacteria Spirochetes Mycobacteria

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

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 pallidum Borrelia burgdorferi Leptospira 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 β-lactam antibiotics Mechanism of action of β-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 β-lactam antibiotic, this process is disrupted. The β-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 β-lactam antibiotics. PBPs recognize and catalyze the peptide bond between two alanine subunits of the peptidoglycan peptide side chain. The β-lactam ring mimics this peptide bond. Thus, the PBPs attempt to catalyze the β-lactam ring, resulting in inactivation of the PBPs.

Six P's by which the action of β-lactams may be blocked: penetration, porins, pumps, penicillinases (β-lactamases), penicillin-binding proteins (PBPs), and peptidoglycan.

The Penicillins Category Parenteral Agents Oral Agents Natural Penicillins Penicillin G Penicillin V Antistaphylococcal penicillins Nafcillin, oxacillin Dicloxacillin Aminopenicillins Ampicillin Amoxicillin and Ampicillin Aminopenicillin + b-lactamase inhibitor Ampicillin-sulbactam Amoxicillin-clavulanate Extended-spectrum penicillin Piperacillin, ticaricillin Carbenicillin Extended-spectrum penicillin + b-lactamase inhibitor Piperacillin-tazobactam, ticaricillin-clavulanate

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 Beechams (1958-60) - development of semi-synthetic penicillins Discovery of clavulanic acid and b-lactamase inhibitors

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STRUCTURE Benzyl penicillin (Pen G) R = Phenoxymethyl penicillin (Pen V) Acyl side chain 6-Aminopenicillanic acid (6-APA) b-Lactam ring Thiazolidine ring Side chain varies depending on carboxylic acid present in fermentation medium present in corn steep liquor Penicillin G Penicillin V (first orally active penicillin)

Folded ‘envelope’ shape Shape of Penicillin G Folded ‘envelope’ shape

Properties of Penicillin G Active vs. Gram +ve bacilli and some Gram -ve cocci Non toxic Limited range of activity Not orally active - must be injected Sensitive to b-lactamases (enzymes which hydrolyse the b-lactam ring) Some patients are allergic Inactive vs. Staphylococci Drug Development Aims To increase chemical stability for oral administration To increase resistance to b-lactamases To increase the range of activity

SAR Conclusions Amide and carboxylic acid are involved in binding Carboxylic acid binds as the carboxylate ion Mechanism of action involves the b-lactam ring Activity related to b-lactam ring strain (subject to stability factors) Bicyclic system increases b-lactam ring strain Not much variation in structure is possible Variations are limited to the side chain (R)

Mechanism of action Penicillins inhibit a bacterial enzyme called the transpeptidase enzyme which is involved in the synthesis of the bacterial cell wall The b-lactam ring is involved in the mechanism of inhibition Penicillin becomes covalently linked to the enzyme’s active site leading to irreversible inhibition Covalent bond formed to transpeptidase enzyme Irreversible inhibition

Mechanism of action - bacterial cell wall synthesis NAM NAG L-Ala D-Glu L-Lys Bond formation inhibited by penicillin

Mechanism of action - bacterial cell wall synthesis Cross linking

Mechanism of action - bacterial cell wall synthesis Penicillin inhibits final crosslinking stage of cell wall synthesis It reacts with the transpeptidase enzyme to form an irreversible covalent bond Inhibition of transpeptidase leads to a weakened cell wall Cells swell due to water entering the cell, then burst (lysis) Penicillin possibly acts as an analogue of the L-Ala-g-D-Glu portion of the pentapeptide chain. However, the carboxylate group that is essential to penicillin activity is not present in this portion

Mechanism of action - bacterial cell wall synthesis Alternative theory- Pencillin mimics D-Ala-D-Ala. Normal Mechanism

Mechanism of action - bacterial cell wall synthesis Alternative theory- Penicillin mimics D-Ala-D-Ala. Mechanism inhibited by penicillin

Mechanism of action - bacterial cell wall synthesis Penicillin can be seen to mimic acyl-D-Ala-D-Ala Penicillin Acyl-D-Ala-D-Ala

Penicillin Analogues - Preparation 1) By fermentation vary the carboxylic acid in the fermentation medium limited to unbranched acids at the a-position i.e. RCH2CO2H tedious and slow 2) By total synthesis only 1% overall yield (impractical) 3) By semi-synthetic procedures Use a naturally occurring structure as the starting material for analogue synthesis

Penicillin Analogues - Preparation Penicillin acylase or chemical hydrolysis Fermentation Semi-synthetic penicillins

Penicillin Analogues - Preparation Problem - How does one hydrolyse the side chain by chemical means in presence of a labile b-lactam ring? Answer - Activate the side chain first to make it more reactive Note - Reaction with PCl5 requires involvement of nitrogen’s lone pair of electrons. Not possible for the b-lactam nitrogen.

Problems with Penicillin G It is sensitive to stomach acids It is sensitive to b-lactamases - enzymes which hydrolyse the b-lactam ring it has a limited range of activity

Problem 1 - Acid Sensitivity Reasons for sensitivity 1) Ring Strain Acid or enzyme Relieves ring strain

Problem 1 - Acid Sensitivity Reasons for sensitivity 2) Reactive b-lactam carbonyl group Does not behave like a tertiary amide Tertiary amide Unreactive b-Lactam Folded ring system Impossibly strained X Interaction of nitrogen’s lone pair with the carbonyl group is not possible Results in a reactive carbonyl group

Problem 1 - Acid Sensitivity Reasons for sensitivity 3) Acyl Side Chain - neighbouring group participation in the hydrolysis mechanism Further reactions

Problem 1 - Acid Sensitivity Conclusions The b-lactam ring is essential for activity and must be retained Therefore, cannot tackle factors 1 and 2 Can only tackle factor 3 Strategy Vary the acyl side group (R) to make it electron withdrawing to decrease the nucleophilicity of the carbonyl oxygen Decreases nucleophilicity

Problem 1 - Acid Sensitivity Examples Penicillin V (orally active) electronegative oxygen Better acid stability and orally active But sensitive to b-lactamases Slightly less active than Penicillin G Allergy problems with some patients Very successful semi-synthetic penicillins e.g. ampicillin, oxacillin

Natural penicillins include Penicillin G (parenteral) and Penicillin V (oral) Gram-positive bacteria Streptococcus pyogenes, Viridans group streptococci, Some Streptococcus pneumoniae, Some Enterococci, Listeria monocytogenes Gram-negative bacterai Neisseria meningitidis, Some Haemophilus influenzae Anaerobic bacteria Clostridia spp. (except C. difficile), Antinomyces israelii Spirochetes Treponema pallidum Leptospira spp.

Problem 2 - Sensitivity to b-Lactamases Notes on b-Lactamases Enzymes that inactivate penicillins by opening b-lactam rings Allow bacteria to be resistant to penicillin Transferable between bacterial strains (i.e. bacteria can acquire resistance) Important w.r.t. Staphylococcus aureus infections in hospitals 80% Staph. infections in hospitals were resistant to penicillin and other antibacterial agents by 1960 Mechanism of action for lactamases is identical to the mechanism of inhibition for the target enzyme But product is removed efficiently from the lactamase active site b-Lactamase

Problem 2 - Sensitivity to b-Lactamases Strategy Block access of penicillin to active site of enzyme by introducing bulky groups to the side chain to act as steric shields Size of shield is crucial to inhibit reaction of penicillins with b-lactamases but not with the target enzyme (transpeptidase) Bulky group Enzyme

Problem 2 - Sensitivity to b-Lactamases Examples - Methicillin (Beechams - 1960) ortho groups important Methoxy groups block access to b-lactamases but not to transpeptidases Active against some penicillin G resistant strains (e.g. Staphylococcus) Acid sensitive (no e-withdrawing group) and must be injected Lower activity w.r.t. Pen G vs. Pen G sensitive bacteria (reduced access to transpeptidase) Poorer range of activity Poor activity vs. some streptococci Inactive vs. Gram -ve bacteria

Problem 2 - Sensitivity to b-Lactamases Examples - Oxacillin Oxacillin R = R' = H Cloxacillin R = Cl, R' = H Flucloxacillin R = Cl, R' = F Orally active and acid resistant Resistant to b-lactamases Active vs. Staphylococcus aureus Less active than other penicillins Inactive vs. Gram -ve bacteria Nature of R & R’ influences absorption and plasma protein binding Cloxacillin better absorbed than oxacillin Flucloxacillin less bound to plasma protein, leading to higher levels of free drug

Antistaphylococcal Penicillins include Nafcillin and Oxacillin (parenteral) as well as Dicloxacillin (oral) Gram-positive bacteria Some Staphylococcus aureus, Some Staphylococcus epidermidis

Problem 3 - Range of Activity Factors Cell wall may have a coat preventing access to the cell Excess transpeptidase enzyme may be present Resistant transpeptidase enzyme (modified structure) Presence of b-lactamases Transfer of b-lactamases between strains Efflux mechanisms Strategy The number of factors involved make a single strategy impossible Use trial and error by varying R groups on the side chain Successful in producing broad spectrum antibiotics Results demonstrate general rules for broad spectrum activity.

Problem 3 - Range of Activity Results of varying R in Pen G R= hydrophobic results in high activity vs. Gram +ve bacteria and poor activity vs. Gram -ve bacteria Increasing hydrophobicity has little effect on Gram +ve activity but lowers Gram -ve activity Increasing hydrophilic character has little effect on Gram +ve activity but increases Gram -ve activity Hydrophilic groups at the a-position (e.g. NH2, OH, CO2H) increase activity vs Gram -ve bacteria

Problem 3 - Range of Activity Examples of Aminopenicillins include: Class 1 - NH2 at the a-position Ampicillin and Amoxycillin (Beecham, 1964) Ampicillin (Penbritin) 2nd most used penicillin Amoxycillin (Amoxil)

Problem 3 - Range of Activity Examples of Aminopenicillins Include: Active vs Gram +ve bacteria and Gram -ve bacteria which do not produce b-lactamases Acid resistant and orally active Non toxic Sensitive to b-lactamases Increased polarity due to extra amino group Poor absorption through the gut wall Disruption of gut flora leading to diarrhoea Inactive vs. Pseudomonas aeruginosa Properties

Problem 3 - Range of Activity Prodrugs of Ampicillin (Leo Pharmaceuticals - 1969) Properties Increased cell membrane permeability Polar carboxylic acid group is masked by the ester Ester is metabolised in the body by esterases to give the free drug

Problem 3 - Range of Activity Mechanism PEN C O H 2 M e 3 PEN C O H 2 Formaldehyde PEN C OH O Ester is less shielded by penicillin nucleus Hydrolysed product is chemically unstable and degrades Methyl ester of ampicillin is not hydrolysed in the body - bulky penicillin nucleus acts as a steric shield

The aminopenicillins include Ampicillin (parenteral) as well as Amoxicillin and Ampicillin (both oral) Gram-positive bacteria Streptococcus pyogenes, Viridans streptococci, Some Streptococcus pneumoniae, Some enterococci Listeria monocytogenes Gram-negative bacteria Neisseria meningitidis, Some Haemophilus influenzae, Some Enterobacteriaceae Anaerobic bacteria Clostridia spp. (except C. difficile), Antinomyces israelii Spirochetes Borrelia burgdorferi

b-Lactamase Inhibitors Clavulanic acid (Beechams 1976)(from Streptomyces clavuligerus) Weak, unimportant antibacterial activity Powerful irreversible inhibitor of b-lactamases - suicide substrate Used as a sentry drug for ampicillin Augmentin = ampicillin + clavulanic acid Allows less ampicillin per dose and an increased activity spectrum Timentin = ticarcillin + clavulanic acid

b-Lactamase Inhibitors Clavulanic acid - mechanism of action O H N 2 1 2 N H 3 4 5

b-Lactamase Inhibitors Penicillanic acid sulfone derivatives Sulbactam Tazobactam Suicide substrates for b-lactamase enzymes Sulbactam has a broader spectrum of activity vs b-lactamases than clavulanic acid, but is less potent Unasyn = ampicillin + sulbactam Tazobactam has a broader spectrum of activity vs b-lactamases than clavulanic acid, and has similar potency Tazocin or Zosyn = piperacillin + tazobactam

The aminopenicillins + b-lactamase inhibitor combinations include ampicillin-sulbactam (parenteral) and amoxicillin-clavulanate (oral) Gram-positive bacteria Some Staphylococcus aureus, Streptococcus pyogenes, Viridans streptococci, Some Streptoocus pneumoniae, Some enterococci Listeria monocytogenes Gram-negative bacteria Neisseria spp. Haemophilus influenzae, Many Enterobacteriaceae Anaerobic bacteria Clostridia spp. (except C. difficile), Actinomyces israellii, Bacteroides spp. Spirochetes Borrelia burgdorferi

Problem 3 - Range of Activity Examples of Broad Spectrum Penicillins Class 2 - CO2H at the a-position (carboxypenicillins) Examples R = H CARBENICILLIN R = Ph CARFECILLIN Carfecillin = prodrug for carbenicillin Active over a wider range of Gram -ve bacteria than ampicillin Active vs. Pseudomonas aeruginosa Resistant to most b-lactamases Less active vs Gram +ve bacteria (note the hydrophilic group) Acid sensitive and must be injected Stereochemistry at the a-position is important CO2H at the a-position is ionised at blood pH

Problem 3 - Range of Activity Examples of Broad Spectrum Penicillins Class 2 - CO2H at a-position (carboxypenicillins) Examples TICARCILLIN Administered by injection Identical antibacterial spectrum to carbenicillin Smaller doses required compared to carbenicillin More effective against P. aeruginosa Fewer side effects Can be administered with clavulanic acid

Problem 3 - Range of Activity Examples of Broad Spectrum Penicillins Class 3 - Urea group at the a-position (ureidopenicillins) Examples Azlocillin Mezlocillin Piperacillin Administered by injection Generally more active than carboxypenicillins vs. streptococci and Haemophilus species Generally have similar activity vs Gram -ve aerobic rods Generally more active vs other Gram -ve bacteria Azlocillin is effective vs P. aeruginosa Piperacillin can be administered alongside tazobactam

The Extended Spectrum Penicillins include Piperacillin and Ticarcillin (parenteral) as well as Carbenicillin (oral) Gram-positive bacteria Streptococcus pyogenes, Viridans streptococci, Some Streptococcus pneumoniae, Some enterococci Gram-negative bacteria Neisseria meningitidis, Some Haemophilus influenzae, Some Enterobacteriaceae, Pseudomonas aeruginosa Anaerobic bacteria Clostridia spp. (except C. difficile), Some Bacteroides spp.

Extended-Spectrum Penicillin + b-Lactamase Inhibitor Combinations include:Piperacillin-tazobactam as well as ticarcillin-clavulanate (both pairs are parenteral) Gram-positive bacteria Some Staphylococcus aureus, Streptocosoccus pyogenes, Viridans streptococci, Some Streptococcus pneumoniae, Some enterococci Listeria monocytogenes Gram-negative bacteria Neisseria spp. Haemophilus influenzae, Most Enterobacteriaceae, Pseudomonas aeruginosa Anaerobic bacteria Clostridia spp. (except C. difficile), Bacteroides spp.

CEPHALOSPORINS

1. Introduction Antibacterial agents which inhibit bacterial cell wall synthesis Discovered from a fungal colony in Sardinian sewer water (1948) Cephalosporin C identified in 1961

6. Mechanism of Action The acetoxy group acts as a good leaving group and aids the mechanism

The Cephalosporins Generation Parenteral Agents Oral Agents First-generation Cefazolin Cefadroxil, cephalexin Second-generation Cefotetan, cefoxitin, cefuroxime Cefaclor, cefprozil, cefuroxime axetil, loracarbef Third-generation Cefotaxime, ceftazidime, ceftizoxime, ceftriaxone Cefdinir, cefditoren, cefpodoxime proxetil, ceftibuten, cefixime Fourth-generation Cefepime

8. First Generation Cephalosporins Cephalothin First generation cephalosporin More active than penicillin G vs. some Gram -ve bacteria Less likely to cause allergic reactions Useful vs. penicillinase producing strains of S. aureus Not active vs. Pseudonomas aeruginosa Poorly absorbed from GIT Administered by injection Metabolised to give a free 3-hydroxymethyl group (deacetylation) Metabolite is less active

8. First Generation Cephalosporins Cephalothin - drug metabolism Metabolism Less active OH is a poorer leaving group Strategy Replace the acetoxy group with a metabolically stable leaving group

8. First Generation Cephalosporins Cephaloridine The pyridine ring is stable to metabolism The pyridine ring is a good leaving group (neutralisation of charge) Exists as a zwitterion and is soluble in water Poorly absorbed through the gut wall Administered by injection

8. First Generation Cephalosporins Cefalexin The methyl group at position 3 is not a good leaving group The methyl group is bad for activity but aids oral absorption - mechanism unknown Cefalexin can be administered orally A hydrophilic amino group at the a-carbon of the side chain helps to compensate for the loss of activity due to the methyl group

First Generation Cephalosporins Cefazolin Cefadroxil Cefalexin

First Generation Cephalosporins include Cefazolin (parenteral) as well as cefadroxil and cephalexin (oral). Gram-positive bacteria Streptococcus pyogenes, Some virdans streptococci, Some Staphylococcus aureus, Some Streptococcus pneumoniae Gram-negative bacteria Some Eschericia coli, Some Klebsiella pneumoniae, Some Proteus mirabilis

9. Second Generation Cephalosporins 9.1 Cephamycins Cephamycin C Isolated from a culture of Streptomyces clavuligerus First b-lactam to be isolated from a bacterial source Modifications carried out on the 7-acylamino side chain

9. Second Generation Cephalosporins 9.1 Cephamycins Cefoxitin Broader spectrum of activity than most first generation cephalosporins Greater resistance to b-lactamase enzymes The 7-methoxy group may act as a steric shield The urethane group is stable to metabolism compared to the ester Introducing a methoxy group to the equivalent position of penicillins (position 6) eliminates activity.

9. Second Generation Cephalosporins 9.2 Oximinocephalosporins Cefuroxime Much greater stability against some b-lactamases Resistant to esterases due to the urethane group Wide spectrum of activity Useful against organisms that have gained resistance to penicillin Not active against P. aeruginosa Used clinically against respiratory infections

Second generation The second-generation cephalosporins have a greater Gram-negative spectrum while retaining some activity against Gram-positive cocci. They are also more resistant to beta-lactamase. Cefaclor (Ceclor, Distaclor, Keflor, Raniclor) Cefonicid (Monocid) Cefprozil (cefproxil; Cefzil) Cefuroxime (Zinnat, Zinacef, Ceftin, Biofuroksym) Cefuzonam

Forms of Cefuroxime (2nd generation cephalosporin) (ZINACEF) Cefuroxime axetil (CEFTIN)

The Second-generation cephalosporins include Cefotetan, cefoxitin, and cefuroxime (all parenteral) as well as Cefaclor, cefprozil, cefuroxime axetil, and loracarbef (all oral). Gram-positive bacteria True cephalosporins have activity equivalent to first-generation agents. Cefoxitin and cefotetan have little activity Gram-negative bacteria Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Haemophilus influenzae, Neisseria spp. Anaerobic bacteria Cefoxitin and cefotetan have moderate anaerobic activity.

10. Third Generation Cephalosporins Oximinocephalosporins Aminothiazole ring Aminothiazole ring enhances penetration of cephalosporins across the outer membrane of Gram -ve bacteria May also increase affinity for the transpeptidase enzyme Good activity against Gram -ve bacteria Variable activity against Gram +ve cocci Variable activity vs. P. aeruginosa Lack activity vs MRSA Generally reserved for troublesome infections

10. Third Generation Cephalosporins Oximinocephalosporins Ceftazidime Injectable cephalosporin Excellent activity vs. P. aeruginosa and other Gram -ve bacteria Can cross the blood brain barrier Used to treat meningitis

The Third-generation Cephalosporins include Cefotaxime, ceftazidime, ceftizoxime, and ceftriaxone (all parenteral) as well as Cefdinir, cefditoren, cefpodoxime proxetil, ceftibuten, and cefixime (all oral). Gram-positive bacteria Streptococcus pyogenes, Viridans streptococci, Many Streptococcus pneumoniae, Modest activity against Staphylococcus aureus Gram-negative bacteria Escherichia coli, Klebsiella pneumoniae, Proteus spp. Haemophilus influenzae, Neisseria spp. Some Enterobacteriaceae. Anaerobic bacteria Atypical bacteria Spirochetes Borrelia burgorferi

11. Fourth Generation Cephalosporins Oximinocephalosporins Zwitterionic compounds Enhanced ability to cross the outer membrane of Gram negative bacteria Good affinity for the transpeptidase enzyme Low affinity for some b-lactamases Active vs. Gram +ve cocci and a broad array of Gram -ve bacteria Active vs. P. aeruginosa

Fourth Generation Cephalosporins include cefepime (parenteral). Gram-positive bacteria Streptococcus pyogenes, Viridans streptococci, Many Streptocossus pneumoniae. Modest activity against Staphylococcus aureus Gram-negative bacteria Escherichia coli, Klebsiella pneumoniae, Proteus spp. Haemophilus influenzae, Neisseria spp. Many other Enterobacteriaceae, Pseudomonas aeruginosa. Anaerobic bacteria Atypical bacteria

Newer b-Lactam Antibiotics Thienamycin (Merck 1976)(from Streptomyces cattleya) Potent and wide range of activity vs Gram +ve and Gram -ve bacteria Active vs. Pseudomonas aeruginosa Low toxicity High resistance to b-lactamases Poor stability in solution (ten times less stable than Pen G)

Newer b-Lactam Antibiotics Thienamycin analogues used in the clinic Imipenem Ertapenem(2002) Meropenem

The Carbapenems include Imipenem/cilstatin, Meropenem, and Ertapenem (all parenteral) Gram-positive bacteria Streptococcus pyogenes, Viridans group streptococci, Streptococcus pneumoniae, Modest activity against Staphylococcus aureus, Some enterococci, Listeria monocytogenes Gram-negative bacteria Haemophilus influenzae, Neisseria spp., Enterobacteriaceae, Pseudomonas aeruginosa Anaerobic bacteria Bacteroides fragilis, Most other anaerobes.

Newer b-Lactam Antibiotics Clinically useful monobactam Aztreonam Administered by intravenous injection Can be used for patients with allergies to penicillins and cephalosporins No activity vs. Gram +ve or anaerobic bacteria Active vs. Gram -ve aerobic bacteria

The Monobactams include only Aztreonam, which is parenteral Gram-positive bacteria Gram-negative bacteria Haemophilus influenzae, Neisseria spp. Most Enterobacteriaceae, Many Pseudomonas aeruginosa. Anaerobic bacteria Atypical bacteria

Vancomycin

Mechanism of Action of Vancomycin Vancomycin binds to the D-alanyl-D-alanine dipeptide on the peptide side chain of newly synthesized peptidoglycan subunits, preventing them from being incorporated into the cell wall by penicillin-binding proteins (PBPs). In many vancomycin-resistant strains of enterococci, the D-alanyl-D-alanine dipeptide is replaced with D-alanyl-D-lactate, which is not recognized by vancomycin. Thus, the peptidoglycan subunit is appropriately incorporated into the cell wall.

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Antimicrobial Activity of Vancomycin Gram-positive bacteria Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pyogenes. Viridans group streptococci, Streptococcus pneumoniae, Some enterococci. Gram-negative bacteria Anaerobic bacteria Clostridium spp. Other Gram-positive anaerobes. Atypical bacteria

Daptomycin Daptomycin is a lipopeptide antibiotic Approved for use in 2003 Lipid portion inserts into the bacterial cytoplasmic membrane where it forms an ion-conducting channel.

Antimicrobial Activity of Daptomycin Gram-positive bacteria Streptococcus pyogenes, Viridans group streptococci, Streptococcus pneumoniae, Staphylococci, Enterococci. Gram-negative bacteria Anaerobic bacteria Some Clostridium spp. Atypical

Rifamycins Rifampin is the oldest and most widely used of the rifamycins Rifampin is also the most potent inducer of the cytochrome P450 system Therefore, Rifabutin is favored over rifampin in individual who are simultaneously being treated for tuberculosis and HIV infection, since it will not result in oxidation of the antiviral drugs the patient is taking Rifaximin is a poorly absorbed rifamycin that is used for treatment of travelers’ diarrhea.

The Rifamycins include Rifampin, Rifabutin, Rifapentine, and Rifaximin, all of which can be administered orally. Rifampin can also be administered parenterally. Gram-positive bacteria Staphylococci Gram-negative bacteria Haemophilus influenzae, Neisseria meningitidis Anaerobic bacteria Mycobacteria Mycobacterium tuberculosis, Mycobacterium avium complex, Mycobacteriumleprae.

Aminoglycosides The structure of the aminoglycoside amikacin. Features of aminoglycosides include amino sugars bound by glycosidic linkages to a relatively conserved six-membered ring that itself contains amino group substituents.

Bacterial resistance to aminoglycosides occurs via one of three mechanisms that prevent the normal binding of the antibiotic to its ribosomal target: Efflux pumps prevent accumulation of the aminoglycoside in the cytosol of the bacterium. Modification of the aminoglycoside prevents binding to the ribosome. Mutations within the ribosome prevent aminoglycoside binding.

The Aminoglycosides include Streptomycin, Gentamicin, Tobramycin, and Amikacin (all parenteral), as well as Neomycin (oral). Gram-positive bacteria Used synergistically against some: Staphylococci, Streptococci, Enterococci, and Listeria monocytogenes Gram-negative bacteria Haemophilus influenzae, Enterobacteiaceae, Pseudomonas aeruginosa Anaerobic bacteria Atypical bacteria Mycobacteria Mycobacterium tuberculosis, Mycobacterium avium complex.

Macrolides and Ketolides The structures of erythromycin and telithromycin Circled substituents and distinguish telithromycin from the macrolides. Substituent allows telithromycin to bind to a second site on the bacterial ribosome.

The macrolide group consists of Erythromycin, Clarithromycin, and Azithromycin (all oral, with erythromycin and azithromycin also being available parenterally). Gram-positive bacteria Some Streptococcus pyogenes. Some viridans streptococci, Some Streptococcus pneumoniae. Some Staphylococcus aureus. Gram-negative bacteria Neiseria spp. Some Haemophilus influenzae. Bordetella pertussis Anaerobic bacteria Atypical bacteria Chlamydia spp. Mycoplasma spp. Legionella pneumophila, Some Rickettsia spp. Mycobacteria Mycobacterium avium complex, Mycobacterium leprae. Spirochetes Treponema pallidum, Borrelia burgdorferi.

The related ketolide class consists of Telithromycin (oral). Gram-positive bacteria Streptococcus pyogenes, Streptococcus pneumoniae, Some Staphylococcus aureus Gram-negative bacteria Some Haemophilus influenzae, Bordetella pertussis Anaerobic bacteria Atypical bacteria Chlamydia spp. Mycoplasma spp. Legionella pneumophila

The Tetracycline Antibiotics The structure of tetracycline

The Tetracycline Class of Antibiotics consists of Doxycycline and Tigecycline (parenteral) as well as Tetracycline, Doxycycline and Minocycline (oral) Gram-positive bacteria Some Streptococcus pneumoniae Gram-negative bacteria Haemophilus influenzae, Neisseria meningitidis Anaerobic bacteria Some Clostridia spp. Borrelia burgdorferi, Treponema pallidum Atypical bacteria Rickettsia spp. Chlamydia spp.

Tigecycline

The antimicrobial activity of Tigecycline (parenteral) Gram-positive bacteria Streptococcus pyogenes. Viridans group streptococci, Streptococcus pneumoniae, Staphylococci, Enterococci, Listeria monocytogenes Gram-negative bacteria Haemophilus influenzae, Neisseria spp. Enterobacteriaceae Anaerobic bacteria Bacteroides fragilis, Many other anaerobes Atypical bacteria Mycoplasma spp.

Chloramphenicol

The Antimicrobial Activity of Chloramphenicol Gram-positive bacteria Streptococcus pyogenes, Viridans group streptococci. Some Streptococcus pneumoniae Gram-negative bacteria Haemophilus influenzae, Neisseria spp. Salmonella spp. Shigella spp. Anaerobic bacteria Bacteroides fragilis. Some Clostridia spp. Other anaerobic Gram-positive and Gram negative bacteria Atypical bacteria Rickettsia spp. Chlamydia trachomatis, Mycoplasma spp.

Clindamycin

The Antimicrobial Activity of Clindamycin (both oral and parenteral) Gram-positive bacteria Some Streptococcus pyogenes, Some viridans group streptococci. Some Streptococcus pneumoniae, Some Staphylococcus aureus Gram-negative bacteria Anaerobic bacteria Some Bacteroides fragilis, Some Clostridium spp. Most other anaerobes. Atypical bacteria

Streptogramins

The Antimicrobial Activity of Quinupristin/Dalfopristin (parenteral) Gram-positive bacteria Streptococcus pyogenes, Viridans group streptococci, Streptococcus pneumoniae, Staphylococcus aureus, Some enterococci. Gram-negative bacteria Anaerobic bacteria Atypical bacteria

The structure of Linezolide The Oxazolidinones The structure of Linezolide

The Antimicrobial Activity of Linezolid (both oral and parenteral) Gram-positive bacteria Streptococcus pyogenes. Viridans group streptococci, Streptococcus pneumoniae, Staphylococci, Enterococci. Gram-negative bacteria Anaerobic bacteria Atypical bacteria

The related ketolide class consists of Telithromycin (oral). Gram-positive bacteria Gram-negative bacteria Anaerobic bacteria Atypical bacteria

The related ketolide class consists of Telithromycin (oral). Gram-positive bacteria Gram-negative bacteria Anaerobic bacteria Atypical bacteria