Lecture 5 - antibiotics.pdf

8/19/2019 Lecture 5 - antibiotics.pdf

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Antibiotics and

Chemiotherapeutics

Antibiotics - Still Miracle

Drugs


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Paul Ehrlich’s Magic Bullets

Salvarsan No. 606

Selective Toxicity

Drugs that specifically target microbial processes, and

not the human host cellular processes


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AntibioticsAntibiotics - antimicrobials of microbial origins, most of the

produced by fungi or bacteria (Streptomyces)Antimicrobial, antimicrobic- any suspastance with

sufficient antimicrobial activity, used in treatment ofinf.dis

Bactericidal – that kill bacteriaBacteriostatic – inhibit growth, not kill bacteria

Chemotherapeutics –encompasses antibiotics,antimicrobial, drugs used in the teratment of cancer; not

natural, created in lab.Semisynthetic drugs – antibiotics that are chemicalymodified

Narrow spectrum / broad spectrum


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Selective Toxicity

Mechanisms and sitesMechanism of action

1. Bacterial cell wall

2. Nucleic acid synthesis

3. Protein synthesis

4. Cell membrane

5. Folic acid synthesisc


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tigecycline

daptomycin


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Svaki lek poseduje dva imena:

Generičko – univerzalno u svetu (pr.amoxicillin)

Zaštićeno, koje daje fabrika koja pravi

Most antibiotics have 2 names, the trade or brand name,

created by the drug company that manufactures the drug, and a

generic name, based on the antibiotic's chemical structure or

chemical class. Trade names such as Keflex and Zithromax are

capitalized. Generics such as cephalexin and azithromycin arenot capitalized.


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Inhibition of Cell wall synthesis – Bacteria cell wall unique in

construction

• Contains peptidoglycan

– Antimicrobials that interfere with the

synthesis of cell wall do not interfere

with eukaryotic cell

• Due to the lack of cell wall inanimal cells and differences in cell

wall in plant cells

– These drugs have very high therapeutic

index

• Low toxicity with high effectiveness – Antimicrobials of this class include

• β lactam drugs

• Vancomycin

• Bacitracin

• Isoniazide, ethambutol - TBC

1.


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Target- Cell Wall SynthesisThe bacterial cell wall is a cross linked polymer called

peptidoglycan which allows a bacteria to maintain its

shape despite the internal turgor pressure caused by

osmotic pressure differences.If the peptidoglycan fails to crosslink the cell wall will lose

its strength which results in cell lysis.

All β-lactams disrupt the synthesis of the bacterial cell

wall by interfering with the transpeptidase which

catalyzes the cross linking process.


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Peptidoglycan

Peptidoglycan is a carbohydrate composed of alternating

units of NAMA and NAGA.

The NAMA units have a peptide side chain which can be

cross linked from the L-Lys residue to the terminal D-Ala-D-Ala link on a neighboring NAMA unit.

This is done directly in Gram (-) bacteria and via a

pentaglycine bridge on the L-lysine residue in Gram (+)

bacteria.


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Inhibition of Cell wall synthesis

• Penicillins and cephalosporins

– Part of group of drugs called β –lactams

• Have shared chemical

structure called β-lactam ring

– Competitively inhibits function

of penicillin-binding proteins

• Inhibits peptide bridge

formation between glycan

molecules

• This causes the cell wall to

develop weak points at the

growth sites and become

fragile.

1.


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MECHANISMS OF ACTION OF

inhibitors of cell wall synthesis

The weakness in the cell wall

causes the cell to lyze.

1.


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Beta lactam antibiotics

1.


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Antibiotics that inhibit cell wall

synthesisBeta lactam antibiotics (BLA) - 4 groups:

• Penicillins

• Cephalosporins

• Carbapenems

• Monobactams

1.


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1. Antibiotics that inhibit cell wall synthesis

Beta lactam antibiotics - Penicillins

– Natural (penicillin G and V)

– Semisynthetic (ampicillin, carbenicillin,

antistaphylococcal ..)

• Structure

– Thiazolidine ring

– Beta-lactam ring

– Variable side chain)


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The R group is responsible forthe activity of the drug, and

cleavage of the beta-lactam

ring will render the drug

inactive.

Antibiotics that inhibit cell wall synthesis

Chemical structure of penicillins

Beta lactam ring


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• The cephalosporins – broad spectrum

– Chemical structures make them resistant to

inactivation by certain β-lactamases – Tend to have low affinity to penicillin-binding proteins

of Gram + bacteria, therefore, are most effective

against Gram – bacteria.

– Chemically modified to produce family of relatedcompounds

• First, second, third, fourth and fifth generation

cephalosporins

Beta lactam antibiotics -

cephasloposrins1.


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Antibiotics that inhibit cell wall synthesis

Beta lactam antibiotics -Carbapenems

Imipenem and others

Activity– broad spectrum

Resistant to most beta lactamasis

Indication – therapy of very serious infetions caused by

multiploresistant bacteria

1.


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Bacteria can produce enzyme

penicillinases (beta Lactamases) that

can destroy BLA

1.


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• Vancomycin

– Inhibits formation of glycan chains

• Inhibits formation of peptidoglycans and cell wall construction

• Does not cross lipid membrane of Gram -

– Gram - organisms innately resistant

– Important in treating infections caused by penicillin resistant Gram +organisms

– Must be given intravenously due to poor absorption from intestinaltract

Antibiotics that inhibit cell wall1.


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Antibiotics that inhibit cell wall

• Bacitracin – inhibits first phases in cell

wall synthesis – bactericidal

• Toxicity limits use to topical applications

• active against Gram +

• Isoniazid –for TBC treatment• Ethambutol - for TBC treatment

1.


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• Polymyxin B, Colistin (Gram negatives)

– Topical

– Combined with bacitracin and neomycin

(broad spectrum) in over-the-counter

preparation

2. Injury to the Plasma Membrane

New - daptomycin


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2. Polymyxin: Antibacterial activity

• However, the polymyxins are only active againstgram negative bacteria (P. aeruginosa, E. coli, K. pneumoniae), while daptomycin is used to treat

gram positive bacteria• The polymyxins are highly nephrotoxic and are

thus only used topically


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2. Polymyxins: Mechanism of action

• Bind the the lipopolysaccharide in the outermembrane, thus destroying OM integrity.

• Bind to the cytoplasmic membrane (to thephosphatidylethanolamine) and make the membrane

more permeable.


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3. Inhibition

of protein

synthesis


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• Inhibition of protein synthesis

– Structure of prokaryotic ribosome acts as target for many

antimicrobials of this class

• Differences in prokaryotic and eukaryotic ribosomes responsible for

selective toxicity – Drugs of this class include

• Aminoglycosides

• Tetracyclins

• Macrolids

• Chloramphenicol• Oxazolidines - lincosamide

3. Inhibition of protein synthesis


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3. Sites of inhibition on the procaryotic ribosome


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3. Inhibition of Protein synthesis

Aminoglycosides • Aminoglycosides

– Irreversibly binds to 30Sribosomal subunit

• Causes distortion andmalfunction of ribosome

• Blocks initiation translation – Causes misreading of

mRNA

– Not effective againstanaerobes, enterococci andstreptococci

– Often used in synergistic

combination with β-lactamdrugs

• Allows aminoglycosides toenter cells that are oftenresistant


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Aminoglycosides

– Examples of aminoglycosidesinclude

• Gentamicin, streptomycin

and tobramycin

– Side effects with extended

use include• Otto toxicity

• Nephrotoxicity


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• Tetracyclins – Reversibly bind 30S ribosomal subunit

• Blocks attachment of tRNA to ribosome

– Prevents continuation of protein synthesis

– Effective against certain Gram + and Gram - – Newer tetracyclines such as doxycycline have longer half-life

• Allows for less frequent dosing

– Resistance due to decreased accumulation by bacterial cells

– Can cause discoloration of teeth if taken as young child


Tetracyclins


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Tetracycline

• Broad spectrum and low cost

• Commonly used to treat sexually transmitteddiseases and intracellular bacteria

• Minor side effect – gastrointestinal disruption• Doxycicline


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Tigecycline – new tetracycline


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Macrolides - Erythromycin • Macrolids

– Reversibly binds to 50Sribosome

• Prevents continuationof protein synthesis

– Effective against variety ofGram + organisms andthose responsible foratypical pneumonia

– Often drug of choice forpatients allergic topenicillin

– Macrolids include

• Erythromycin,clarithromycin andazithromycin


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Oxazolidines - Linezolid

Active against

resistant Gram

positive

bacteria


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– Binds to 50S ribosomal subunit

• Prevents peptide bonds from

forming and blocking proteins

synthesis• Bacteriostatic agent

– Effective against a wide variety of

organisms

– Generally used as drug of lastresort for life-threatening

infections

– Rare but lethal side effect is

aplastic anemia


Chloramphenicol


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3. Mupirocin (90% Pseudomonic acid A)

• Isolated from Pseudomonas fluorescens

• Mupirocin works against Gram-positive bacteria only

• Can be used to treat MRSA (although resistance is

rising)

• Mupirocin inhibits bacterial isoleucyl-tRNA synthetase.


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Products containing Mupirocin


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• Inhibition of nucleic acid synthesis

– These include

•Fluoroquinolones

•Rifamycins

4. Inhibitors of Nucleic Acid

Synthesis


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• Fluoroquinolones

– Inhibit action of topoisomerase DNA gyrase

• Topoisomerase maintains supercoiling of

DNA

– Effective against Gram -; newer also against

Gram +

– Examples include• Ciprofloxacin and ofloxacin

• There are 4 generation of fluoroquinolones

4. Inhibitors of Nucleic Acid Synthesis


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Fluorohinoloni

Inhibiraju enzimsku aktivnost dva predstavnika topoizomeraza:

DNK giraze (topoizomeraze II) i topoizomeraze IV (dovode do superuvrtanja DNK

lanca u hromozmu i plazmidima bakterija i održavaju DNK u stabilnoj formi)

Superuvrnutost DNK utiče na njenu replikaciju i prepis gena

Posledica - inhibicija replikacije bakt. DNK i ev. degradacija DNKDNK giraza konvertuje relaksiranu

dvolančanu formu DNK u negativno

superuvrnutu (obrnuti smer

dvostrukog heliksa)

Aktivnost je u fazama:

1. Pozitivno superuvrtanje

2. Seče lance DNK

3. Provlači DNK kroz prolazni dvolančani

prekid i vrši negativno superuvrtanje –

energetski stabilna forma

Fluoroquinolones - Inhibits DNA gyrase


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• Rifamycins

– Block prokaryotic RNA polymerase

• Block initiation of transcription

– Rifampin most widely used rifamycins

– Effective against many Gram + and some Gram - as well as members

of genus Mycobacterium

– Primarily used to treat tuberculosis and Hansen’s disease (lepra) aswell as preventing meningitis after exposure to N. meningitidis

4. Inhibitors of Nucleic Acid

Synthesis

hibi i f b li h f li


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5. Inhibition of metabolic pathways – folic

acid synthesis

• Inhibition of metabolic pathways

– Relatively few

– Most useful are folateinhibitors

• Mode of actions to inhibit

the production of folicacid

– Antimicrobials in this classinclude

• Sulfonamides

• Trimethoprim


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Sulfonamides compete with PABA for the active

site on the enzyme.

The sulfonamide Sulfamethoxazole is commonly usedin combination with trimethoprim


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Drugs used for treatment of TBC are

Antitubercular drugs (tuberculostatics)

Several compaunds with different mechanism of actionTreatment must be administered over a prolonged

period; and the use of several anti-TB drugs is required.

First line tuberculostatic drug (bactericidal, except

etanbutol)

Isoniazid, rifampicin, streptomycin, ethambutol, pyrazinamid

Very effective with low toxicity

Second line tuberculostatic drug

PAS, ethionamide, amikacin, kanamycin, fluorochinolones

Less effective and toxic


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What is antibiotic resistance?


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Antimicrobial Resistance

• Intrinsic• Acquired - relative or complete

lack of effect of antimicrobial

against a previously susceptiblemicrobe


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• Enzymatic destruction of drug

• Alteration of drug's target site

• Prevention of penetration of drug

• Rapid ejection of the drug (efflux)

Mechanisms of Antibiotic

Resistance


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Mechanism of bacterial resistance


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Mechanisms of bacterial resistance

1. Enzymatic destruction of drug:Beta lactamasis inactivate beta lactam

antibiotics

Esterasis inactivates macrolides

Acetyltransferase, adenyltransferase

inactivate aminoglycosides

Produkcija beta


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1

Porin

Peptidoglikan

Periplazmatski prostorPBP

Beta lactam

antibiotics

Beta Lactamases

1


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1

1


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1

ß -lactamase


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2. Mechanisms of bacterial resistance

Alteration of targets:Alteration of penicilllin binding proteins

(PBPs) – resistance to BLA

Alteration of ribosomes – resistance to

macrolides, tetracyclines

Alteration of DNA gyrases – resistance to

fluorochinolones


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Binding to targets (PBP) (PVP)

PBP


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ß – Lactam antibiotic

Vezivanje BLA za

PVP


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Inactive PBP

Inhibition of peptidoglycan synthesis

High affinity

for PBP

)


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High affinity to PBP

Cell wall destructionBacterial death

)


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ß – Lactam antibiotic

Vezivanje BLA za ciljna mesta (PVP)


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Low affinity to PBP

Active PBP

Synthesis of PG


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3. Mechanisms of bacterial resistance

Decreaseses uptake in bacterial cells –

A. Decreased infflux (Gram negativebacteria, due to porins)

B. Increased efflux


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Outside

Inside

Porins in Gram negative bacteria

Efflux pump protein transport both in Gram positive and Gram

negative bacteria i kod Gram negativnih

Protein

chanell

Efflux pump

Porini kod Gram negativnih bakterija i proteinski transportni sistem kod efluks


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outside

inside

antibiotic

pumpe

PorinsEfflux pump


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outside

inside

Excreted antibiotic

porins Efflux pump

Antibiotic


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Mechanisms of Resistance in

Beta Lactam antibiotics• Altered target (Gram negative/positive)

• Altered permeability (Gram negative)

• Production of inactivating enzymes (Gramnegative/positive)


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Beta lactamases

Over than 340 different beta laktamazses

They cleave beta lactam ring and destroy BLA

Gram negative bacteria

are main producers ; they

store these anzymes in

periplasmatic space

Bakterije iz familije Enterobacteriaceae (E.coli, Klebsiella...) i Pseudomonas

stvaraju brojne beta laktamaze

Bacteria in Enterobacteriacea family (E.coli, Klebsiella) and

Pseudomonas are main beta lactamases producers


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Beta lactamases

Depending on group of beta lactam antibiotics that is their main

target beta lactamses colud be

penicilinases cephalosporinases carbapenemases

Due to emergence of new beta-lactamases, there was a need for

the synthesis of new drugs

Rusult: after a short time, bacteria sucseed to develop new, more

powerful beta lactamases

Eg. Wide Spectrum Beta Lactamses (mid 1970s)

Extended spectrum beta lactamses (ESBLs) – 1990

Metallo betalactamses

Carbapenemases

Antibiotic Resistance


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Figure 20.20

Intermicrobial transfer of plasmids, transposons and chromosiomal DNA containing

resistance genes (R factors) occurs by conjugation, transformation,and transduction


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Transfer of genetic material – spreeding

bacterial resistance


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h


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What Factors Promote

Antimicrobial Resistance?• Exposure to sub-optimal levels of

antimicrobial• Inappropriate use

• Exposure to microbes carrying

resistance genes


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Inappropriate Antimicrobial Use

• Prescription not taken correctly

• Antibiotics for viral infections

• Antibiotics sold without

medical supervision

• Spread of resistant microbes

in hospitals due to lack of hygiene


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Inappropriate Antimicrobial Use

• Inadequate surveillance or defectivesusceptibility assays

• Poverty or war• Use of antibiotics in foods

• Lack of quality control in manufacture or

outdated antimicrobial

Antibiotics in animal feeds


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Antibiotics in animal feeds


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Antibiotics in Foods

• Antibiotics are used in animal feeds and

sprayed on plants to prevent infection and

promote growth• Multi drug-resistant Salmonella typhi has

been found in 4 states in 18 people who

ate beef fed antibiotics


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Antibiotic Drug and Host Interaction

• Toxicity to organs

• Allergic reactions

• Suppress/alter microflora

• Effective drugs

Tetracycline treatments


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Tetracycline treatments

can cause teeth discoloration.

Disrupting the normal flora in the intestine can result in

superinfections.


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Finding an effective drug for

treatment

• Identify infectious agent

• Perform sensitivity testing

• Often the Minimum Inhibitory

Concentration (MIC) is determined


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Proposals to Combat Antimicrobial

Resistance

• Speed development of new antibiotics

• Track resistance data nationwide• Restrict antimicrobial use

• Direct observed dosing (TB)


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Proposals to Combat Antimicrobial

Resistance

• Use more narrow spectrum antibiotics

• Use antimicrobial cocktails

MRSA – nosocomial pathogen –


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till ~1996, since than it became community

acquired

Documents

Lecture 5 - antibiotics.pdf