Beta Lactam Antibiotics

Presentation by:Saurav Chandra SarmaInt. Ph.D NCU 3rd Sem.

Outline

1• What is Antibiotic???

• Bacterial cell structure

2

• Beta-lactam Antibiotics and it’s mode of action

• Resistance to Beta lactam Antibiotics

• Examples

3

• Beta-lactamases and its classification

• Proposal

• Conclusion.!!!

Antibiotics and it’s Classification

Antibiotics

•An antibiotic is an agent that either kills or inhibits the growth of a microorganism.

•Excludes substances that kill bacteria but that are not produced by microorganisms such as Gastric juices & Hydrogen Peroxide.

•Also excludes synthetic antibacterial compound such as sulfonamides.

•Penicillin is the first natural antibiotic discovered by Alexander Fleming in 1928.

Classification of Antibiotics

Based on mode of Action

Bacteriostatic Bactericidal

Based on their spectrum of

action

Broad-spectrumNarrow

Spectrum

Source: Google Images

Types of Antibiotics(Based on their mode of action)

Bacteriostatic Antibiotics

• Tetracyclines

• Spectinomycin

• Sulphonamides

• Macrolides

• Chloramphenicol

• Trimethoprim

Bactericidal Antibiotics

• Penicillins

• Cephalosporins

• Fluoroquinolones(Ciprofloxacin)

• Glycopeptides (Vancomycin)

• Monobactams

• Carbapenems

Types of Antibiotics(Based on their structural similarities)

Antibiotics: Mode of Action

•Inhibitors of DNA synthesis

•Inhibitors of bacterial protein synthesis

•Inhibitors of bacterial cell wall synthesis

•Interference with metabolism

•Impairment of nucleic acids

Antibiotic Targets

Sourcs: Microbiology: A Clinical Approach

Bacterial Cell structure

Gram positive vs. Gram negative bacteria

Source: Google Images

Cell Wall

Source: Google Images

Structure of Peptidoglycan layer

•Peptidoglycan is a carbohydrate composed of alternatingunits of NAMA and NAGA.

•The NAMA units have a peptide side chain which can becross linked from the L-Lys residue to the terminal D-Ala-D-Ala link on a neighboring NAMA unit.

Source: Google Images

Transpeptidase Enzyme

•The cross linking reaction is catalyzedby a class of transpeptidases known aspenicillin binding proteins

•A critical part of the process is therecognition of the D-Ala-D-Alasequence of the NAMA peptide sidechain by the PBP. Interfering with thisrecognition disrupts the cell wallsynthesis.

•β-lactams mimic the structure of theD-Ala-D-Ala link and bind to the activesite of PBPs, disrupting the cross-linking process.

Source: Google Images

Transpeptidation mechanism

Source: Google Images

Transpeptidation mechanism

Source: Google Images

Beta–lactam Drugs

Beta-Lactam Antibiotics

β-lactam ring

•Contains a beta-lactam ring in their molecular structures.

•Nitrogen is attached to the beta carbon relative to the carbonyl ring and hence the name.

Classification

•Penicillins

•Cephalosporins

•Other β-Lactam drugs

--Cephamycins--Carbapenems--Oxacephalosporins--β-Lactamase inhibitors--Monolactams

Beta-Lactam Structure

How do they work?

1. The β-lactam binds to Penicillin Binding Protein (PBP)

2. PBP is unable to crosslink peptidoglycanchains

3. The bacteria is unable to synthesize a stable cell wall

4. The bacteria is lysed

Mechanism of β-Lactam Drugs

• The amide of the β-lactam ring is unusuallyreactive due to ring strain and a conformationalarrangement which does not allow the lone pair ofthe nitrogen to interact with the double bond ofthe carbonyl.

• β-Lactams acylate the hydroxyl group on the serineresidue of PBP active site in an irreversible manner.

• This reaction is further aided by the oxyanion hole,which stabilizes the tetrahedral intermediate andthereby reduces the transition state energy.

Discovery of Penicillin(First beta-lactam drug)

•Discovered in 1928.

• While working in his lab, trying to kill a deadly bacteria,he noticed a

blue mold growing on the dish

•Learned that it was the mold Penicillum Notatum.

•Penicillin is found in this mold.

•Noticed that the bacteria around the mold was dissolving.Source: Google Images

How it is was Developed

• For 9 years, nobody could purify the Penicillum Notatumto get the pure penicillin.

Finally, in 1938, a team of Oxford University Scientists, headed by Howard Florey and Ernst B. Chain helped to develop penicillin.

Source: Google Images

Mechanism of β-Lactam Drugs

• The amide of the β-lactam ring is unusually reactive due to ring strain and a conformational arrangement which does not allow the lone pair of the nitrogen to interact with the double bond of the carbonyl.

• β-Lactams acylate the hydroxyl group on the serine residue of PBP active site in an irreversible manner.

• This reaction is further aided by the oxyanion hole, which stabilizes the tetrahedral intermediate and thereby reduces the transition state energy.

Mechanism of β-Lactam Drugs

The hydroxyl attacks the amide and forms a tetrahedral intermediate.

Mechanism of β-Lactam Drugs

The tetrahedral intermediate collapses, the amide bond is broken, and the nitrogen is reduced.

Mechanism of β-Lactam Drugs

The PBP is now covalently bound by the drug and cannot perform the cross linking action.

Penicillin

Natural Penicillin

Penicillin V (Phenoxymethylpenicillin)

EFFECTIVE AGAINST:

• Gram positive + Less effective against Gram negative bacteria

TREATMENT FOR:

• Tonsillitis

• Anthrax

• Rheumatic fever

• Streptococcal skin infections

CHARACTERISTICS:

• Narrow spectrum

• Should be given orally

• Prone to beta-lactamase

Penicillin V (Phenoxymethylpenicillin)

EFFECTIVE AGAINST:

• Gram positive + Less effective against Gram negative bacteria

TREATMENT FOR:

• Tonsillitis

• Anthrax

• Rheumatic fever

• Streptococcal skin infections

CHARACTERISTICS:

• Narrow spectrum

• Should be given orally

• Prone to beta-lactamase

Amino-Penicillin

Ampicillin R=Ph

Amoxicillin R= Ph-OH

Ampicillin

EFFECTIVE AGAINST:• Gram positive + Gram negative

bacteriaTREATMENT FOR:• Ear infection• Sinusitis• Urinary tract infections• MeningitisCHARACTERISTICS:• Broad spectrum• Can be given orally and

parenterally• Prone to beta-lactamase

Ampicillin

Sulbactam

+

llUnasyn

Amoxicillin

EFFECTIVE AGAINST:• Gram positive + Gram negative

bacteriaTREATMENT FOR:• Skin infection• Sinusitis• Urinary tract infections• Streptococcal pharyngitisCHARACTERISTICS:• Broad spectrum• Can be given orally and parenterally• Prone to beta-lactamaseSIDE-EFFECTS:• Rash, diarrhea, vomiting, nausea,

edema, stomatitis, and easy fatigue.

Amoxicillin

Clavulanic Acid

+

ll

Augmentin

Anti-Staphylococcal Penicillin

Methicillin

EFFECTIVE AGAINST:

• Gram positive bacteria

TREATMENT FOR:

CHARACTERISTICS:

• Very narrow Spectrum

• Should be given parenterally

SIDE-EFFECT:

• Interstitial nephritis

Oxacillin

EFFECTIVE AGAINST:

• Gram positive bacteria

TREATMENT AGAINST:

• penicillin-resistant Staphylococcus aureus

CHARACTERISTICS:

• Very narrow Spectrum

• Should be given parenterally

SIDE-EFFECT:

• Hypersensitivity and local reactions

• In high doses, renal, hepatic, or nervous system effects can occur

Nafcillin

EFFECTIVE AGAINST:

• Gram positive bacteria

TREATMENT AGAINST:

• Staphylococcal infections

CHARACTERISTICS:

• Very narrow Spectrum

• Should be given parenterally

SIDE-EFFECT:

• Allergic reactions

• Nausea and vomiting

• Abdominal pain

Cloxacillin

EFFECTIVE AGAINST:

• Staphylococci that produce beta-lactamase

CHARACTERISTICS:

• Very narrow Spectrum

• Should be given orally

SIDE-EFFECT:

• Allergic reaction

Dicloxacillin

EFFECTIVE AGAINST:

• Gram positive bacteria + Staphylococci that produce beta-lactamase

CHARACTERISTICS:

• Very narrow Spectrum

• Should be given orally

SIDE-EFFECT:

• Allergic reaction

• Diarrhoea, nausea, rash, urticariapain and inflammation at injection site

Flucloxacillin

EFFECTIVE AGAINST:

• Gram positive bacteria + Staphylococci that produce beta-lactamase

CHARACTERISTICS:

• Very narrow Spectrum

• Should be given orally

SIDE-EFFECT:

• Allergic reaction

• Diarrhoea, nausea, rash, urticariapain and inflammation at injection site

Anti-Pseudomonal Penicillin

Piperacillin

EFFECTIVE AGAINST:

• Gram positive +Gram negative

CHARACTERISTICS:

• Extended Spectrum

• Should be given by intravenous or intramuscular injection

SIDE-EFFECT:

• Hypersensitivity

• Gastrointestinal

• Renal

• Nervous system

*Piperacillin+Tazobactam=Zosyn

Carbenicillin

EFFECTIVE AGAINST:

• Gram negative + Limited Gram positive

TREATMENT FOR:

• Urinary tract infections

CHARACTERISTICS:

• Highly soluble in water and acid-labile

SIDE-EFFECT:

• High doses can cause bleeding

• Hypokalemia

Ticarcillin

EFFECTIVE AGAINST:

• Mainly gram negative bacteria particularly Pseudomonas aeruginosa

TREATMENT FOR:

• Stenotrophomonas maltophiliainfections

CHARACTERISTICS:

SIDE-EFFECT:

• Diarrhoea

• Bleeding

• Fever

• Fainting

Cephalosporin

These has been conventionally classified into four generations based on Generation system

• This is based on chronological sequence of development, but more importantly ,takes into consideration the overall antibacterial spectrum as well as potency.

• First-generation cephalosporins are predominantly active against Gram-positive bacteria, and successive generations have increased activity against Gram-negative bacteria (albeit often with reduced activity against Gram-positive organisms).

First Generation Cephalosporins

Cefalothin Cefalexin

Cefadroxil Cefazolin

Second Generation Cephalosporins

Cefuroxime(Oral) Cefotetan

Third Generation Cephalosporins

Cefotaxime Ceftriaxone

Ceftazidime

Fourth Generation Cephalosporins

Cefepime

Carbapenem

What are carbapenems

• Carbapenems are a class of beta-lactam antibiotics with a broad spectrum of antibacterial activity. They have a structure that renders them highly resistant to beta-lactamases. Carbapenem antibiotics were originally developed from thienamycin, a naturally-derived product of Streptomycescattleya.

57Dr.T.V.Rao MD

Carbapenems common uses

• Imipenem– Broad spectrum, covers Gram-positive, Gram-negative

(including ESBL-producing strains), Pseudomonas and anaerobes

• Meropenem– Less seizure-inducing potential, can be used to treat CNS

infections

• Ertapenem– Lacks activity vs. Acinetobacter and Pseudomonas

– Has limited activity against penicillin-resistant pneumococci

58Dr.T.V.Rao MD

Imipenem

EFFECTIVE AGAINST:

• Aerobic and anaerobic, Gram positive and gram negative bacteria

CHARACTERISTICS:

• Broad Spectrum

• Intravenous

• Resistant to beta-lactamaseenzymes

SIDE-EFFECT:

• Seizuregenic at high doses

Meropenem

EFFECTIVE AGAINST:

• Aerobic and anaerobic, Gram positive and gram negative bacteria

CHARACTERISTICS:

• Ultra Broad Spectrum

• Intravenous

• Resistant to beta-lactamaseenzymes

SIDE-EFFECT:

• Diarrhoea

• Vomiting

• headache

Ertapenem

EFFECTIVE AGAINST:

• Gram positive and gram negative bacteria

CHARACTERISTICS:

• Broad Spectrum

• Intravenous

• Resistant to beta-lactamaseenzymes

• Not active against MRSA

SIDE-EFFECT:

• Convulsions

• Seizures

• headache

Monobactam

Aztreonam

EFFECTIVE AGAINST:

• Gram positive +Gram negative+Anaerobic bacteria

CHARACTERISTICS:

• Broad Spectrum

• Intravenous

• Resistant to beta-lactamaseenzymes

• Not active against MRSA

SIDE-EFFECT:

• Diarrhoea

• Nausea

• Vomiting

BETA-LACTAMASE INHIBITORS

• Resemble β-lactam antibiotic structure

• Bind to β-lactamase and protect the antibiotic from destruction

• Most successful when they bind the β-lactamase irreversibly

• Three important in medicine:

» Clavulanic Acid

» Sulbactam

» Tazobactam

Beta–lactam Resistance

Resistance-The Global Battle.!!!

What is Resistance?

•Drug resistance refers to unresponsiveness of a microorganism to an antimicrobial agent.

•Drug resistance are of two types:---Natural Resistance---Acquired Resistance

Natural Resistance:

•Some microbes have always been resistant to certain anti-microbial agent.•They lack the metabolic process or the target side thai is affected by particular drug.

E.g: Gram negative bacilli are normally unaffected by Penicillin G.M. tuberculosis is insensitive to Tetracyclines.

•This type of resistance does not pose significant clinical problem.

Acquired Resistance:

•It is the development of resistance by an organism which was sensiive before due to the use of antimicrobial agent over a period of time.•This can happen with any microbe and is a major clinical problem.However, the development of resistance is dependent on the microorganism as well as the drug.

Porins

Altered penicillin binding proteins

b-lactamases

MECHANISMS OF RESISTANCE

MECHANISMS FOR ACQUIRING

RESISTANCE

69

CHALLENGES OF b-LACTAMASES

1940 : Introduction of penicillins

1940 : First description of b-lactamases published

1944 : Strains of staphylococcus aureus producing

b-lactamase

1960s : Clinical use of expanded spectrum penicillins

- such as ampicillin and carbenicillin

1970s : plasmid mediated b-lactamases assumed prominence in

enterobacteriaceae and gram-negative bacteria

1980-90 : Development of broad-spectrum cephalosporins, cephamycins,

monobactams and carbapenems

1990 : Increased resistance among gram-negative bacteria with inducible

chromosomally-mediated b lactamases

JAC (1993); suppl A: 1-8

Beta–lactamases

Beta-Lactamase Enzyme

Functional Classification

Group 1 (Cephalosporinases*)

Group 2 (Penicillinases,

Cephalosporinases)

Group 3 (Metalloenzymes*)

Group 4 (Penicillinases*)

* Not inhibited by Clavulanic Acid

Beta-Lactamase Enzyme

Molecular Classification

Serine Based

Class A Class C Class D

Metallo

B-lactamases

Class B

Beta-Lactamase Enzyme

Molecular Classification

Serine Based

Class A Class C Class D

Metallo

B-lactamases

Class B

ESBLs are enzymes that mediate resistance to extended-spectrum (third generation) cephalosporins (e.g., ceftazidime, cefotaxime, and ceftriaxone) and monobactams (e.g., aztreonam) but do not affect cephamycins(e.g., cefoxitin and Cefotetan) or carbapenems(e.g., meropenem or imipenem).

Extended spectra Beta-Lactamase(ESBL)

WHY SHOULD WE DETECT THESE ENZYMES?

• The presence of an ESBL-producing organism in a clinical infection can

result in treatment failure if one of the above classes of drugs is used.

• ESBLs can be difficult to detect because they have different levels of

activity against various cephalosporins. Thus, the choice of which

antimicrobial agents to test is critical. For example, one enzyme may

actively hydrolyze ceftazidime, resulting in ceftazidime minimum

inhibitory concentrations (MICs) of 256 µg/ml, but have poor activity on

cefotaxime, producing MICs of only 4 µg/ml.

• If an ESBL is detected, all penicillin's, cephalosporins, and aztreonam

should be reported as resistant, even if in vitro test results indicate

susceptibility

RISK FACTORS FOR ESBL INFECTION

• Length of hospital stay

• Severity of illness

• Time in the ICU

• Intubation and mechanical ventilation

• Urinary or arterial catheterization

• Previous exposure to antibiotics

Metallo Beta-lactamase

• Resistant against broad spectrum of beta-lactam antibiotics

• These include the antibiotics of the carbapenem family.

• This class of β-lactamases is characterized by the ability to

hydrolyze carbapenems and by its resistance to the

commercially available β-lactamase inhibitors but susceptibility

to inhibition by metal ion chelators.

• The most common bacteria that make this enzyme are Gram

negative such as Escherichia coli and Klebsiella pneumoniae ,

Pseudomonas aeroginosa.

BETA-LACTAMASE INHIBITORS

• Resemble β-lactam antibiotic structure

• Bind to β-lactamase and protect the antibiotic from destruction

• Most successful when they bind the β-lactamase irreversibly

• Three important in medicine:

» Clavulanic Acid

» Sulbactam

» Tazobactam