Other cell wall acting agents

1. Antibiotics Acting on Cell Wall:
Vancomycin, Bacitracin, Cycloserine and
Fosfomycin
Dr Ravi Kant Agrawal, MVSc, PhD
Senior Scientist (Veterinary Microbiology)
Food Microbiology Laboratory
Division of Livestock Products Technology
ICAR-Indian Veterinary Research Institute
Izatnagar 243122 (UP) India

2. β-lactamase inhibitors
Clavulenic acid, Sulbactum, Tazobactum
• Although beta-lactamase inhibitors have
little antibiotic activity of their own, they
instead inhibit the activity of beta-
lactamases produced by bacteria
• In particular, clavulenic acid is an
irreversible, "suicide" inhibitor of beta-
lactamase.
• They are used with a beta-lactam
antibiotic to extend their spectrum of
activity.
• They are potent inhibitors of many
bacterial beta-lactamases and can protect
hydrolyzable penicillins from inactivation
by these enzymes.
• They are included in combination with
amoxycillin (Augmentin; Co-amoxyclav) or
with ticaricillin (Timentin).

3. Clavulanic acid
• Isolated from Streptomyces clavuligerus
• No antibacterial activity.
• Powerful and irreversible inhibitor of most β-lactamases as
such is now used in combination with traditional penicillins
such as amoxycillin: Co-Amoxyclavc, Augmentin.
• The structure of clavulanic acid was the first example of a
naturally occurring β-lactam ring which was not fused to a
sulfur-containing ring but fused to an oxazolidine ring
structure.
• Clavulanic acid is a suicide inhibitor, covalently bonding to
a serine residue in the active site of the β-lactamase leads to
formation of the acyl-enzyme intermediate.
• This is more reactive species that is attacked by another amino
acid in the active site permanently inactivating the enzyme.
• The mechanism requires the loss or gain of protons at various
stages and an amino acid such as histidine present in the active
site would be capable of acting as a proton donor/acceptor.

4. Tazobactam
• It is combined with the extended spectrum beta-
lactam antibiotic piperacillin in the drug Tazocin (also Zosyn,
Piprataz).
• It broadens the spectrum of piperacillin by making it effective
against organisms that express beta-lactamase and would
normally degrade piperacillin.
• Tazobactam sodium is a derivative of the penicillin nucleus and
is a penicillanic acid sulfone.

5. Sulbactum
• Sulbactam is an irreversible inhibitor of beta-lactamase
• It binds the enzyme and does not allow it to interact with the
antibiotic.
• Sulbactam is able to inhibit the most common forms of beta-
lactamase
• It confers little protection against bacteria such as Pseudomonas
aeruginosa, Citrobacter, Enterobacter and Serratia, which often
express this gene.
• Sulbactum + Ampicillin = Unacyn
-Lactam/-Lactamase Inhibitor: Pharmacology
• Clavulanate, Sulbactam – Moderately well absorbed
• Good tissue distribution
• Penetration into inflamed meninges
– Clavulanate, Sulbactam – Poor
– Tazobactam – Good in animal model
• Excretion
– Clavulanate – Lung, feces, urine
– Sulbactam, Tazobactam - Urine

6. Commercially Available
They are available only in fixed combinations with specific
penicillins:
• Ampicillin + sulbactam (Unasyn)
• Amoxicillin + clavulanic acid (Co-amoxyclav, Augmentin)
• Ticarcillin + clavulanate potassium (Timentin)
• Piperacillin + tazobactam sodium (Tazocin, Zosyn, Piprataz)

7. Other cell wall active agents
BacitracinHistory:
• Isolated by John T. Goorley in 1943.
• Isolated from Bacillus subtilis
• Found in the infected compound fracture of the patient Margaret
Tracy
• Bacitracin is a Polypeptide antibiotic: Complex Cyclic peptide
• Bactericidal drug
Mechanism of action
• Binds to the transport protein bactoprenol after it inserts a
peptidoglycan monomer into the growing cell wall.
• Bacitracin interferes with the dephosphorylation of the C55-
isoprenyl pyrophosphate of bactoprenol after it releases the
monomer it has transported across the membrane.
• Bactoprenol molecules that have not lost the second phosphate
group cannot assemble new monomers and transport them
across the cytoplasmic membrane.
• As the autolysins continue to break the peptide cross-links and
new cross-links fail to form, the bacterium bursts from osmotic
lysis.

8. Bacitracin…..Uses:
• Active against Gram (+) organisms e.g.
S. aureus and Streptococci
• Most Gram negative organisms are
resistant
• Its action is on Gram-positive cell walls.
• Topical application due to
nephrotoxicity and poor absorption.
• Effective topically, and is a common
ingredient of mouth, nose, eye and skin
antibiotic preparations.
• Often used for traumatic abrasions.
• 500 units/g ointment + PolymyxinB or
Neomycin
Side effects:
• Nephrotoxicity
• It can cause contact dermatitis and
cross-reacts with allergic sensitivity to
sulfa-drugs.

9. Vancomycin
Vancomycin is a ‘glycopeptide’ originally
obtained from Streptomyces orientalis.
MOA:
Glycopeptides such as VANCOMYCIN and the
lipoglycopeptide TEICHOPLANIN bind to the
D-Ala-D-Ala portion of the pentapeptides of
the peptidoglycan monomers and block the
formation of glycosidic bonds between the
sugars by the transglycosidase enzymes, as
well as the formation of the peptide cross-
links by the transpeptidase enzymes.
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.
This results in a weak cell wall and
subsequent osmotic lysis of the bacterium.

10. • Water soluble and quite stable
• Poorly absorbed from the GIT
• 99% excreted by glomerular filtration: Renal elimination
• T1/2: 6-10 days – not removed by dialysis.
• Synergistic with Gentamicin and Streptomycin against E. faecium
and E. faecalis strains that do not exhibit high levels of
aminoglycoside resistance.
Vancomycin: Pharmacokinetics

11. Vancomycin Uses
 Narrow-spectrum, active against methicillin-resistant
staphylococci (MRSA), pseudo-membranous colitis caused by
Clostridium difficile and strains of penicillin-resistant
Streptococcus pneumoniae.
 Prophylaxis for subacute bacterial endocarditis in penicillin
allergic patients for high risk surgery
 Vancomycin can be administered orally: Oral only for
pseudomembranous colitis, antibiotic associated enterocolitis
caused by C. difficile
 For systemic infections: Vancomycin is administered IV
 Dose: 0.125 – 0.25 gm/ q 6 hrs.
 Vancomycin can also be used to treat anearobic Gram + bacteria,
including (in the case of a GI infection).
 Used for treatment of oxacillin resistant G+ infections.
 Combined with Cefotaxime, Ceftriaxone or Rifampicin for the
treatment of meningitis suspected or known to be caused by a
highly penicillin resistant strain of pneumococcus.
 Vancomycin cannot be used to treat Gram –ve bacteria, since the
large size of the vancomycin molecule prohibits its passing of the
outer membrane.

12. Dose:
• Recommended dosage
is 30 mg/kg/day in two
or three divided doses
• Adults with normal
renal function – 1 g
every 12 hrs
Children – 40 mg/kg/d
in 3 to 4 divided doses

13. – Must monitor blood levels to ensure therapeutic levels and
prevent toxicity
– Monitor I/V site closely: Causes phlebitis, chills and fever.
– May cause ototoxicity and nephrotoxicity
– Should be infused over 60 minutes
– Rapid infusions may cause hypotension
– Rapid infusion of drug may lead to “RED MAN SYNDROME OR
RED NECK SYNDROME” - Flushing/itching of head, neck, face,
upper trunk
• Anti-histamine may be ordered to reduce these effects
• Monitor trough levels carefully
– Ensure adequate hydration (2 L fluids/24 hr) if not
contraindicated to prevent nephrotoxicity.
Vancomycin: Adverse Effect

14. • Resistance – modification of the D-Ala-D-Ala binding site of the peptidoglycan
building block in which the terminal D-Ala is replaced by D-lactate/D-serine
resulting to loss of a critical H bond that facilitates high affinity binding of
vancomycin to its target and loss of activity.
Intrinsic resistance
 Pentapetide end with D-Ala-D-Lac: Leuconostoc, Lactobacillus, Pediococcus
Or with D-Ala-D-Ser: Enetrococcus gallinarum, Enetercoccus caselliflavus
Acquired resistance
 A thickening of the PG layer
 Modification of the PG termini from D-Ala--D-Ala to D-Ala--D-lactate
 Gene (vanA, B, C, D, G, E) is carried on plasmids and may be transferred from
organism to organism
 Importance
 VRE - vancomycin resistant E. faecium, E. faecalis
 VRSA - vancomycin resistant S. aureus (1st clinical case reported in 2002 in US)
 VISA - vancomycin intermediately resistant S. aureus
 GISA - Glycopeptide intermediately resistant S. aureus
• Resistance: Emerging Vancomycin resistance: VRE and VRSA
Vancomycin Resistance

15. Mechanism of Resistance to Vancomycin
Vancomycin-susceptible S. aureus (VSSA): Vancomycin MIC*: < 2 μg/ml.
Vancomycin-intermediate S. aureus (VISA): Vancomycin MIC: = 4-8 μg/ml.
Vancomycin-resistant S. aureus (VRSA): Vancomycin MIC: >16 μg/ml.

16. 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
Antimicrobial Activity of Vancomycin

17. Newer glycopeptide antibiotics
• Telavancin
– Derived from vancomycin
– active versus Gram-positive bacteria including strains with
reduced susceptibility to vancomycin
• Teicoplanin
– It can be given intramuscularly
• Dalbavancin
– Derived from teicoplanin
– Effective on methicillin-resistant and vancomycin-
intermediate S. aureus (VISA).

18. Other cell wall active agents
Cycloserine
• Analog of D -alanine
• The terminal two amino acid residues of the Murein precursor consist of D-
Alanine which is produced by the enzyme Alanine Racemase and the two
residues are joined by D-alanine Ligase.
• STRUCTURAL ANALOGS OF D-ALANINE AND INHIBITS INCORPORATION OF
D-ALANINE INTO PEPTIDOGLYCAN PENTAPEPTIDE BY INHIBITING ALANINE
RACEMASE WHICH CONVERTS L ALANINE TO D ALANINE AND D-ALANYL-D-
ALANINE LIGASE.
• Both enzymes are competitively inhibited by D-cycloserine.
• Highly toxic
Clinical uses:
• Used against drug resistant tuberculosis caused by M. tuberculosis resistant
to first line agents.
Pharmacokinetics:
• Water soluble; very unstable at acid pH.
• Widely distributed into tissues
• Excreted through the urine
• 0.5 – 1 g /d in 2 – 3 divided doses
• Causes dose related CNS toxicity, headaches, tremors, acute psychocis,
convulsions

19. Fosfomycin
• Inhibits a very early stage of bacterial cell wall synthesis
• Fosfomycin inhibits bacterial cell wall biogenesis by inactivating
the enzyme UDP- N-Acetylglucosamine-3-enol pyruvyl
transferase also known as MurA.
• This enzyme catalyzes the step in peptidoglyacan biosynthesis
namely the ligation of Phosphoenol pyruvate (PEP) to the 3'-
hydroxyl group of UDP-N-Acetyl Glucosamine.
• Blocks formation of NAM from NAG by inhibition of Pyruvyl
transferase.
• This pyruvate moiety provides the linker that bridges the glycan
and peptide portion of peptidoglycan.
• Fosfomycin is a PEP analog; that inhibits MurA by Alkylating an
active site Cysteine residue.

20. • Drug is transported into the cell by glycerophosphate or glucose
6 phosphate transport systems
• Resistance is due to inadequate transport of drug into the cell
Activity and Uses:
• Active against both Gram (+) and Gram (-)
• In vitro synergism with beta lactams, aminoglycosides or
fluoroquinolones
• Available orally ( 2-4 g, single dose in uncomplicated UTI) and
parenterally
• Excreted through the kidneys
• Safe in pregnancy

22. Thanks
Acknowledgement: All the material/presentations available online on the
subject are duly acknowledged.
Disclaimer: The author bear no responsibility with regard to the source
and authenticity of the content.