antimicrobial agents sofronio agustin professor sofronio agustin professor lectures in microbiology...
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Antimicrobial AgentsAntimicrobial Agents
Sofronio Agustin
Professor
Sofronio Agustin
Professor
LECTURES IN MICROBIOLOGYLECTURES IN
MICROBIOLOGY
LESSON 8LESSON 8
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Lesson 8 TopicsLesson 8 Topics
Antimicrobial Therapy
Selective Toxicity
Survey of Antimicrobial Agents
Microbial Drug Resistance
Drug-Host Interaction
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The Ideal Antimicrobial DrugThe Ideal Antimicrobial Drug
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Selective ToxicitySelective Toxicity
An ideal in chemotherapy that an
antimicrobial drug kills only pathogenic
microbes without harming the host.
Historically, reminiscent of the “magic bullet” of Paul Ehrlich.
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Terms in ChemotherapyTerms in Chemotherapy
Chemotherapy - use of drugs to treat diseases.
Antimicrobials - any drug used in treating infectious diseases.
Antibiotics - substances produced by somemicrobes that inhibit or kill other microbes.
Synthetic drugs - antimicrobial compounds synthesized in the laboratory.
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Historical Note in ChemotherapyHistorical Note in Chemotherapy
1928 – Alexander Fleming discovered penicillin from Penicillium notatum.
1940 – Howard Florey and Ernst Chain performed first clinical trials of penicillin.
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AntibioticsAntibiotics
Naturally occurring Metabolic products of bacteria and fungiReduce competition for nutrients and space
Examples:
Bacteria- Streptomyces, Bacillus
Molds -Penicillium, Cephalosporium
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Antimicrobial ActivityAntimicrobial Activity
Narrow-spectrum
Broad-spectrum
Bactericidal
Bacteriostatic
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Antimicrobial ActivityAntimicrobial Activity
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Modes of ActionModes of Action
Primary target sites of antimicrobial drugs in bacterial cells.
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Cell Wall Active AgentsCell Wall Active Agents
Bactericidal
Penicillin and Cephalosporins – binds and blocks
peptidases involved in cross-linking the glycan
molecules.
Vancomycin – prevents peptidoglycan elongation
Cycloserine – inhibits the formation of the basic
peptidoglycan subunits
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Cell Wall Active AgentsCell Wall Active Agents
Antibiotics weaken the cell wall and cause the cell to lyse.
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Cell Wall Active AgentsCell Wall Active Agents
Penicillins and cephalosporins destroy the peptidoglycan layer by disrupting the peptide cross bridges.
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Cell Wall Active AgentsCell Wall Active Agents
Penicillin Natural penicillins Semi-synthetic penicillins
Molecular Structure Thiazolidine ring Beta-lactam ring Variable side chain (R group)
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PenicillinsPenicillins
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PenicillinasePenicillinase
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PenicillinsPenicillins
Penicillinase-resistant penicillins
Extended-spectrum penicillins
Penicillins + -lactamase inhibitors
Carbapenems
Monobactam
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PenicillinsPenicillins
BactericidalNarrow spectrum.
Used to treat:
Streptococcal
Staphylococcal
Meningococcal, and
Spirochaete infections.
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CephalosporinsCephalosporins
Derived from Cephalosporium acremonium
Beta lactam antibiotic
like penicillin
Main ring different
from penicillin 2 sites for R groups
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CephalosporinsCephalosporins
Inhibit cell wall synthesis
Broad-spectrum or extended spectrum
antibiotic
2nd, 3rd, 4th generations more effective
against Gram-negatives
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CephalosporinsCephalosporins
Different R groups allow for versatility and improved effectiveness of cephalosporins.
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Polypeptide AntibioticsPolypeptide Antibiotics
Bacitracin
Topical application
Effective against Gram-positives
Vancomycin
Glycopeptide
Important "last line" against antibiotic resistant S. aureus
Hinders peptidoglycan elongation
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Mycolic Acid InhibitorsMycolic Acid Inhibitors
Antimycobacterial antibiotics
Isoniazid (INH) - inhibits mycolic acid synthesis
Ethambutol - inhibits incorporation of
mycolic acid into cell wall
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Inhibition of Protein SynthesisInhibition of Protein Synthesis
Various antibiotics and their sites of protein synthesis inhibition on the prokaryotic ribosome.
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Inhibitors of Protein SynthesisInhibitors of Protein Synthesis
Aminoglycosides
Broad-spectrum antibioticsChanges shape of 30S subunit
Treatment of bubonic plague,STD, and Gram-negative infections
Examples: Streptomycin, neomycin,
gentamycin
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Aminoglycoside StructureAminoglycoside Structure
Amino sugars and a six-carbon ring (aminocyclitol) in Streptomycin.
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Streptomyces Streptomyces
Streptomyces sp.
synthesizes many
antibiotics such
as:
aminoglycosides,
tetracycline,
chloramphenicol,
and erythromycin.
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Tetracycline Tetracycline
Broad spectrum
Interferes with tRNA attachment
Treat intracellular infections
Risk to pregnant women
Chemical Structure of Tetracycline
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Chloramphenicol Chloramphenicol
Broad-spectrumBinds 50S subunit,
inhibits peptide bond formation
Cheap syntheticTreat typhoid fever Side effects: Aplastic
anemia
Nitrobenzene ring of chloramphenicol
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Erythromycin Erythromycin
A macrolide
Bactericidal
Binds 50s, prevents
translocation
Gram positives
Side effects:
GI
disturbance
Lactone ring of erythromycin
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Streptogramins Streptogramins
A combination drug of quinopristin and dalfopristin
Bactericidal
Binds 50s, inhibits translation
Affect Gram-positives
Example: Synercid
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Oxazolidinones Oxazolidinones
Bactericidal
Binds 50S, prevents formation of 70S
ribosome
Affect Gram-positives
Example: Linezolid
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Injury to Cell MembraneInjury to Cell Membrane
PolymyxinsInteract with membrane phospholipidsTopicalCombined with Bacitracin and Neomycin as over-the counter antibiotic
Amphotericin BAnit-fungal agentForms complexes with sterols in the membraneCauses cytoplasmic leakageCan affect human cell membranes (toxicity)
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Nucleic Acid Synthesis InhibitorsNucleic Acid Synthesis Inhibitors
RifamycinInhibits RNA synthesis
Anti-tuberculosis drug
Quinolones and fluoroquinolones
inhibits DNA unwinding enzymes (gyrases)
Urinary tract infectionsCiprofloxacin
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Nucleic Acid Synthesis InhibitorsNucleic Acid Synthesis Inhibitors
Chloroquinebinds and cross-links the double helixanti-malarial
Quinolones - e.g. Cirpofloxacininhibits DNA unwinding enzymes (gyrases)
Azidothymidine (AZT)AntiviralAnalogs of purines and pyrimidines
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Sulfa Drugs Sulfa Drugs
Analogs of important metabolites (folic acid)
Competitive enzyme inhibition
Prevents the metabolism of DNA, RNA, and amino acid
Examples: Sulfonamides, and
trimethoprim
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Sulfa Drugs Sulfa Drugs
Sulfonamides compete
with PABA for the active
site on the enzyme.
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SulfonamidesSulfonamides
Attachment of
different R groups
to the main
structural nucleus
affords versatility
of sulfonamides.
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SulfonamidesSulfonamides
Synthetic drug derived from dyes
(Prontosil of Domagk)
Synergistic combination as
Trimethoprim/Sulfamethoxazole
Treatment of pneumonia in AIDS
patients
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Antifungal Drugs Antifungal Drugs
(a) Polyenes (b) Azoles (c) Fluorocytosine
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Antifungal Drugs Antifungal Drugs
Amphotericin B
Polyene derivativeAffects sterols in fungal membraneCauses cytoplasmic leakage
Can affect human cell membranes
(nephrotoxicity)
For systemic fungal infections
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Antifungal Drugs Antifungal Drugs
Azoles- Miconazole, Triazoles
Inhibit ergosterol synthesis
For cutaneous fungal infections
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Antifungal Drugs Antifungal Drugs
Echinocandins
Inhibit synthesis of -glucan, cell wall component in yeasts
Used against Candida and Pneumocystis infections
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Antifungal Drugs Antifungal Drugs
Fluorocytosine (5-FC)
Cytosine analog, interferes with RNA synthesis
Used in serious systemic fungal infections
For Amphotericin B resistant fungi
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Antifungal Drugs Antifungal Drugs
Pentamidine isothionateMay bind DNA
For Pneumocystis infections
GriseofulvinInhibition of microtubules (mitosis)
For superficial mycoses
Tolnaftate Action unknown
For Athlete’s foot
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Antiprotozoal Drugs Antiprotozoal Drugs
Chloroquine
Inhibits DNA synthesis
For Malaria
Metronidazole
Damages DNA
For Entamoeba, Trichomonas infections
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Antihelminthic Drugs Antihelminthic Drugs
Niclosamide
Prevents ATP generation
For Tapeworms
Praziquantel
Alters membrane permeability
For Flatworms
Pyrantel pamoate
Neuromuscular block
Intestinal roundworms
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Antihelminthic Drugs Antihelminthic Drugs
Mebendazole
Inhibits nutrient absorption
For intestinal roundworms
Ivermectin
Paralyzes worm
For intestinal roundworms
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Antiviral DrugsAntiviral Drugs
Few antiviral drugs available Selective toxicity difficult - viruses are
intracellular in host cellsTargets in viral replication cycle:
-Entry-Nucleic acid synthesis-Assembly and release
Interferons – natural or artificial
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Antiviral DrugsAntiviral Drugs
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Antiviral DrugsAntiviral Drugs
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Antiviral DrugsAntiviral Drugs
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Antiviral DrugsAntiviral Drugs
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Antimicrobial AgentsAntimicrobial Agents
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Antimicrobial AgentsAntimicrobial Agents
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Antimicrobial AgentsAntimicrobial Agents
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Antimicrobial TherapyAntimicrobial Therapy
Identify infectious agentSusceptibility testingMinimum Inhibitory Concentration (MIC)Minimum Bactericidal Concentration
(MBC)
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Kirby-Bauer TestKirby-Bauer Test
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Kirby-Bauer TestKirby-Bauer Test
The Kirby-Bauer Test is used to determine the effectiveness of a drug by measuring the zone of inhibition.
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E-TestE-Test
The E-test as an alternative method to the Kirby-Bauer test
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Dilution MethodsDilution Methods
The dilution test determines actual MIC values.
Correlated with in vivo reactions
More accurate and standardized
Modern micro-dilution
techniques are used in
automated methods.
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MIC MIC
Comparative MIC values for sample bacterial isolates
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Combination Therapy Combination Therapy
Synergism occurs when the effect of two
drugs together is greater than the
effect of either alone.
Antagonism occurs when the effect of two
drugs together is less than the effect
of either alone.
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Synergism Synergism
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Drug-Host InteractionDrug-Host Interaction
Toxicity to organsAllergic reactions
Suppression or alteration of
microbiota
Effective drugs
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Drug-Induced Side EffectsDrug-Induced Side Effects
Tetracycline treatments can cause teeth discoloration
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Disruption of MicrobiotaDisruption of Microbiota
Disrupting the microbiota in the intestine can result in superinfections
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Drug ToxicityDrug Toxicity
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Antimicrobial ResistanceAntimicrobial Resistance
A variety of mutations can lead to antibiotic resistance.
Mechanisms of antibiotic resistance
1. Enzymatic destruction of drug
2. Prevention of penetration of drug
3. Alteration of drug's target site
4. Rapid ejection of the drug Resistance genes are often on plasmids or
transposons that can be transferred between bacteria.
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Antimicrobial ResistanceAntimicrobial Resistance
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Antimicrobial ResistanceAntimicrobial Resistance
Intermicrobial transfer of plasmids bearing resistance genes R factors) by conjugation, transformation, and transduction.
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Natural SelectionNatural Selection
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Antimicrobial ResistanceAntimicrobial Resistance
Misuse of antibiotics selects for resistance mutants. Misuse includes: Using outdated, weakened antibiotics Using antibiotics for the common cold and
other inappropriate conditions Use of antibiotics in animal feed Failure to complete the prescribed regimen Using someone else's leftover prescription
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New ApproachesNew Approaches
To counter emergence of drug resistance
requires new approaches to drug
development.Prevent iron –scavenging
capabilities of microbesInhibit genetic controls (riboswitches)Probiotics and prebiotics
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Future ApproachesFuture Approaches
Antimicrobial peptides- broad spectrum antibiotics from plants and animals
Squalamine (sharks)
Protegrin (pigs)
Magainin (frogs)
Antisense agents -complementary DNA or peptide nucleic acids that binds to a pathogen's virulence gene(s) and prevents transcription