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
• The bacterial cell wall allows the
microorganism to maintain its shape
• The cell wall also provides structural
support to withstand changes in osmotic
pressure.
Classification of Bacteria
• Gram-positive: Stained dark blue by
Gram-staining procedure
• Gram-negative: Don’t 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.
Diagrams of the cell wall structure of Gram-negative (left) and
Gram-positive bacteria. Key: peptidoglycan layer (yellow);
protein (purple); teichoic acid (green); phospholipid ( brown);
lipopolysaccharide (orange).
Figure 1. General overview of lipopolysaccharide (LPS) on the outer membrane of a Gram-negative bacterium. LPS consists of 3
major components: the highly variable outer O-antigen segment; a more conserved core, which is divided into outer and inner
segments; and the bioactive lipid A portion. Variation within the length of the LPS, due to mutational absence of specific structures,
not only changes the phenotypic appearance of the bacterium (i.e., smooth [S], semi-rough [SR], or rough [R]), but may also change
some bioactive responses by the host to the bacterium itself. (A) Some bacterial species contain an outer capsule that protects the
bacterium from host defenses such as complement, lysis, and phagocytosis. (B) Outer lipid bilayer with LPS which is approximately 8
nm in width. (C) Peptidoglycan layer. (D) Inner bilipid membrane. Note: Additional lipoproteins, porin complexes, and additional
membrane proteins established within and surrounding the inner and outer membranes have been removed to simplify the diagram
(Raetz, 1992; Caroff et al., 2002).
Gram-Staining Animation Link
http://student.ccbcmd.edu/courses/bio141/labmanua/lab6/images/gram_stain_11.swf
The Dyes Used in Gram Staining
Methyl Violet 10B Safranin
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.
The Carbohydrate Building Blocks
N-Acetylglucosamine N-Acetylmuraminic Acid
(NAG) (NAM)
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.
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
– Staphylococcus aureus aureus
– Staphylococcus epidermidis
• Streptococci
– Streptococcus pneumoniae
– Streptococcus pyogenes Streptococcus
– Streptococcus agalactiae viridans
– 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 b-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:
(1) penetration,
(2) porins,
(3) pumps,
(4) penicillinases (β-
lactamases),
(5) penicillin-binding
proteins (PBPs),
and
(6) peptidoglycan.
The Penicillins
Category Parenteral Agents Oral Agents
Natural Penicillins Penicillin G Penicillin V
Antistaphylococcal Nafcillin, oxacillin Dicloxacillin
penicillins
Aminopenicillins Ampicillin Amoxicillin and Ampicillin
Aminopenicillin + b- Ampicillin-sulbactam Amoxicillin-clavulanate
lactamase inhibitor
Extended-spectrum Piperacillin, ticaricillin Carbenicillin
penicillin
Extended-spectrum Piperacillin-tazobactam,
penicillin + b-lactamase ticaricillin-clavulanate
inhibitor
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
http://www.microbelibrary.org/microbelibrary/files/ccImages/Articl
eimages/Spencer/spencer_cellwall.html
STRUCTURE
R=
O
CH2 H H H
C N
S Me
Benzyl penicillin (Pen G) R 6-Aminopenicillanic acid
N (6-APA)
R= Acyl side Me
chain O
O CH2 CO2H Thiazolidine
ring
Phenoxymethyl penicillin (Pen V) b-Lactam
ring
Side chain varies depending on carboxylic acid present in fermentation medium
CH2 CO2H Penicillin G
present in corn steep liquor
OCH2 CO2H Penicillin V
(first orally active penicillin)
Shape of Penicillin G
O
Me
C H
R NH
S
Me
O N CO2H
H H
..
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
Amide essential Cis Stereochemistry essential
O
H
C N H H
S Me
R
N Me
O
Carboxylic acid essential
bLactam essential CO2H
Conclusions Bicyclic system essential
• 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
O H H O O
H H H H H H H
C N C N C N
S Me S Me S Me
R R R
Enz-Nu O C HN
Nu N Me N Me Me
-H Nu-Enz
O O
Enz CO2H H CO2H CO2H
Covalent bond formed
to transpeptidase enzyme
Irreversible inhibition
Mechanism of action - bacterial cell wall synthesis
NAM NAG NAM NAG NAM
L-Ala NAM L-Ala
NAG NAM L-Ala
NAG NAM
D-Glu D-Glu D-Glu
L-Ala L-Ala L-Ala
NAM NAG NAM NAG NAM
L-Lys L-Lys L-Lys
D-Glu D-Glu D-Glu
L-Ala L-Ala L-Ala
L-Lys L-Lys L-Lys
D-Glu D-Glu D-Glu
L-Lys L-Lys L-Lys
Bond formation
inhibited by
penicillin
Mechanism of action - bacterial cell wall synthesis
NAM NAG NAM NAG SUGAR
BACKBONE
L-Ala L-Ala
D-Glu D-Glu
L-Lys Gly Gly Gly Gly Gly L-Lys Gly Gly Gly Gly Gly
D-Ala D-Ala
D-Ala D-Ala
PENICI LLI N
TRANSPEPTIDASE
D-Alanin e
NAM NAG NAM NAG SUGAR
BACKBONE
L-Ala L-Ala
D-Glu D-Glu
L-Lys Gly Gly Gly Gly Gly L-Lys Gly Gly Gly Gly Gly
D-Ala D-Ala
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 acts as an analogue of the D-Ala-D-Ala portion of
the pentapeptide chain.
Mechanism of action - bacterial cell wall synthesis
Alternative theory- Pencillin mimics D-Ala-D-Ala.
Normal Mechanism
Peptid e
Peptid e Chain
Chain
Peptide
Peptide Ch ain
Peptid e D-Ala Gly
Chain
Chain
Gly
D-Ala D-Ala CO 2H
D-Ala
OH
OH O H
Mechanism of action - bacterial cell wall synthesis
Alternative theory- Penicillin mimics D-Ala-D-Ala.
Mechanism inhibited by penicillin
Peptide
Ch ain Blocked
Blocked H2 O
O
H O O
R C NH Gly
S Me R C NH H
R C NH H
S Me S Me
N
Me O
O O HN
H
HN Me
CO2H Me
OH CO2H O CO2H
O
Blocked Irreve rsibly blocke d
Mechanism of action - bacterial cell wall synthesis
Penicillin can be seen to mimic acyl-D-Ala-D-Ala
R R
H H
C N H H C N Me
S Me
O O H
H H
N N
Me
O O CH3
CO2H CO2H
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
O
H H
C N
S Me
CH2 Penicillin G
N
Me
O
CO2H
Penicillin acylase
or chemical hydrolysis
H H
H2N
S Me
Fermentation
N Me
O
6-APA CO2H
O
C
R Cl
O
H H H
C N
S Me
R
N
Semi-synthetic penicillins
Me
O
CO2H
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
O
PhCH2 C NH Cl OR
S PCl5 ROH H2O
PhCH2 C N PhCH2 C N 6-APA
N PEN PEN
O
CO2H
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
O
O O
H H H Acid or C
H
N
H H
C
H
N
H H
C N
S Me enzyme R
S Me
R
S Me
R
HO HO2C
N
N Me HN Me
H2O Me
O
O
CO2H
CO2H CO2H
H
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
R R
R
C NR2 C N Unreactive
O O R
b-Lactam Me
S S
Me
Me
O
N
H
CO2H X O
N Me
Folded ring CO2H
Impossibly
system strained
• 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
R
H
C N H R N R N
S S
S
-H
O
O N O HN
N
O
O O H
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
H H
E.W.G. N
S
C
O N
O
Decreases
nucleophilicity
Problem 1 - Acid Sensitivity
Examples
X
PhO CH2
H
N
H
HC
a H H
S N
S
C R C
O N N
electronegative O
O
O
oxygen
Penicillin V X = NH2, Cl, PhOCONH,
(orally active) 2H
Heterocycles, CO
• Better acid stability and orally active • Very successful semi-
• But sensitive to b-lactamases synthetic penicillins
• Slightly less active than Penicillin G e.g. ampicillin, oxacillin
• Allergy problems with some patients
Deep Intramuscular (IM)
Formulations of Penicillin G
Penicillin G benzathine Penicillin G Procaine
Differences between
Bicillin C-R and Bicillin L-A
Bicillin C-R 900/300 (penicillin G benzathine and penicillin G procaine
injectable suspension) contains the equivalent of 900, 000 units of
penicillin G as the benzathine and 300, 000 units of penicillin G as the
procaine salts. It is available for deep intramuscular injection.
Bicillin L-A suspension in the disposable-syringe formulation is viscous
and opaque. It is available in a 1 mL, 2 mL, and 4 mL sizes containing the
equivalent of 600,000, 1,200,000 and 2,400,000 units respectively of
penicillin G as the benzathine salt.
Bicillin L-A (2,400,000 units) is approved for treatment of syphillis,
whereas Bicillin C-R (not sold in 2,400,000 unit size) is not.
A unit of penicillin is defined as that amount which has the same activity
as 0.6 mg of pure penicillin G sodium salt.
Natural penicillins include Penicillin
G (parenteral) and Penicillin V (oral)
Gram-positive Streptococcus pyogenes, Viridans group
bacteria streptococci, Some Streptococcus
pneumoniae, Some Enterococci, Listeria
monocytogenes
Gram-negative Neisseria meningitidis, Some Haemophilus
bacterai influenzae
Anaerobic Clostridia spp. (except C. difficile),
bacteria 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
O O
H H H H
C N C N
S Me S Me
R R
N HO2C HN
Me Me
O b-Lactamase
CO2H CO2H
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)
O
Bulky H H H
C N
group S Me
R
N Me
Enzyme O
CO2H
Problem 2 - Sensitivity to b-Lactamases
Examples - Methicillin (Beecham - 1960)
O
ortho groups H
H H
important MeO
C N
S Me
N Me
OMe
O
CO2H
• 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 - bacteria
Problem 2 - Sensitivity to b-Lactamases
Examples - Oxacillin
R'
O
H H H Oxacillin R = R' = H
C N
S Me Cloxacillin R = Cl, R' = H
R
N
Flucloxacillin R = Cl, R' = F
N Me
Me
O
O
Bulk y and CO2H
e- withdrawing
• Orally active and acid resistant
• Resistant to b-lactamases
• Active vs. Staphylococcus aureus
• Less active than other penicillins
• Inactive vs. Gram - 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
Nafcillin
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
1. Cell wall may have a coat preventing access to the cell
2. Excess transpeptidase enzyme may be present
3. Resistant transpeptidase enzyme (modified structure)
4. Presence of b-lactamases
5. Transfer of b-lactamases between strains
6. 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
1. R= hydrophobic results in high activity vs. Gram + bacteria
and poor activity vs. Gram - bacteria
2. Increasing hydrophobicity has little effect on Gram + activity
but lowers Gram - activity
3. Increasing hydrophilic character has little effect on Gram
+ activity but increases Gram - activity
4. Hydrophilic groups at the a-position (e.g. NH2, OH, CO2H)
increase activity vs Gram - bacteria
Problem 3 - Range of Activity
Examples of Aminopenicillins include:
Class 1 - NH2 at the a-position
Ampicillin and Amoxicillin (Beecham, 1964)
H NH2
H NH2
C
HO C
H H
C N H
C N H
O O
O
O
Ampicillin
(Omnipen, Polycillin, Principen) Amoxicillin (Amoxil)
2nd most used penicillin
Problem 3 - Range of Activity
Examples of Aminopenicillins Include:
Properties
• Active vs Gram + bacteria and Gram - 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 diarrhea
• Inactive vs. Pseudomonas aeruginosa
Amoxicillin
Clarithromycin
(Biaxin)
Lansoprazole
(Prevacid)
•Amoxicillin is sometimes used together with
clarithromycin (Biaxin) to treat stomach ulcers
caused by Helicobacter pylori, a Gram - bacteria
•Also, a stomach acid reducer (lansoprazole, or
Prevacid) is sometimes added.
Helicobacter pylori
Helicobacter pylori is linked to stomach inflammation,
which may also result in gastric ulcers and stomach
cancer
•In the early 20th century, ulcers were believed caused by
stress
•In 1982, Robin Warren and Barry Marshall, two Australian
physicians, suggested link between H. pylori and ulcers
•Medical community was slow to accept (first abstract
describing such results was rejected for a poster)
In 2005, the two researchers, Barry Marshall and J.
Robin Warren, received the Nobel Prize in medicine
for their discovery of the bacterium Helicobacter pylori
and its role in gastritis and peptic ulcer disease
Link
Problem 3 - Range of Activity
Prodrugs of Ampicillin (Leo Pharmaceuticals - 1969)
O
C
R= CH2O CMe3 PIVAMPICILLIN
H NH2
O
C
H TALAMPICILLIN
C N H H R= O
S Me
O
N Me O
O C
R= CH O O CH2Me
CO2R
Me
BACAMPICILLIN
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
O H
H PEN PEN
PEN
C H
C O CH2 O C OH
C O CH2 O CMe3
O O
O
ENZYME
Formaldehyde
• 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
• Assigned Reading:
• Antibiotics Basics for Clinicians by Alan R. Hauser, pp. 1-31.
• Lange, Roland P.; Locher, Hans H.; Wyss, Pierre C.; Then, Rudolf L. The
targets of currently used antibacterial agents: lessons for drug discovery.
Current Pharmaceutical Design (2007), 13(30), 3140-3154. Link
• Levy, Stuart B.; Marshall, Bonnie. Antibacterial resistance worldwide:
Causes, challenges and responses. Nature Medicine (New York, NY,
United States) (2004), 10(12, Suppl.), S122-S129. Link
• Projan S J; Shlaes D M Antibacterial drug discovery: is it all downhill from
here?. Clinical microbiology and infection : the official publication of the
European Society of Clinical Microbiology and Infectious Diseases (2004),
10 Suppl 4 18-22. Link
• Lowy, Franklin D. Antimicrobial resistance: the example of Staphylococcus
aureus. Journal of Clinical Investigation (2003), 111(9), 1265-1273. Link
• Goodman and Gillman’s Pharmaceutical Basis of Therapeutics, Chapter 42,
pp. 1095-1109.
• Goodman and Gillman’s Pharmaceutical Basis of Therapeutics, Chapter 44,
pp. 1127-1143.
• Homework questions
1. List the major antibiotic families and their respective mechanisms of action.
2. With respect to antimicrobial resistance, what is meant by the term ‘selection density’?
3. Why is the presence of antibacterial agents in wastewater a problem and what is a
potential solution to this problem?
4. The actual number of antibacterial targets is probably much larger than that predicted by
a genomic analysis. Explain.
5. What is meant by a ‘promiscuous drug’? In what respect might the b-lactam antibiotics
satisify this definition?
6. Provide several reasons for the current decline in commercial pharmaceutical interest in
developing new antimicrobial products.
7. What is ‘Levy’s Law of Antibiotics’?
8. Name the gene responsible for the production of b-lactamase in Staphylococcus aureus
and its regulators. Name the gene responsible for methicillin resistance. What does this
latter gene code for?
9. What is the difference between bacteriostatic agents and bacteriocidal agents? When
might it be sufficient to use a bacteriostatic agent?
10. Name the three different general mechanisms whereby bacteria acquire resistance.
11. Describe the mechanisms of both vertical and horizontal transfer of resistance
determinants.
12. What is a synergystic combination? Describe such a combination used to treat
enterococcal endocardiditis.
13. What is a superinfection?
14. Compare the structures of Penicillin G, Penicillin V, Ampicillin, and Methicillin, labeling
the key differences and providing the reasons these differences resulted in an improved
drug.