PHAR7: Antimicrobials Flashcards
How do microorganisms cause toxicity?
In the wrong place, with the wrong activity, or in the wrong quantity they can cause toxicity and pathology through exhausting critical resources, invasion and killing of cells, or production of toxins.
List they types of microbes
- Bacteria
- Fungi
- Viruses
- Protoazoa
- Helminths
- Algae
- Prions
List three characteristics of microbes
- May be unicellular or multicellular
- May exist individually as single cells or in colonies
- Are present in all three domains of cellular life (Archaea, Bacteria and Eukarya)
How do bacteria divide?
Binary fission
Out of all the types of microbes, which have a cell wall?
Bacteria (peptidoglycan) and fungi (chitin), the rest do not.
What size of ribosomes do the different types of microbes have?
bacteria have 70S whereas all the others have 80S.
Viruses and prions can be considered as?
Non-cellular
What are the two types of DNA present in bacteria cells?
Plasmids and nucleoids
What does synergy mean?
The interaction of biological structures or substances that produce an overall effect greater than the sum of individual effects of any of them
What other factors can affect the pathology?
- compromised host immunity
- translocation
What are the different types of bacterial shapes?
- coccus
- dilococci
- tetrad
- streptococci
- coccobacillus
- filamentous
- staphylococci
- bacillus
- diplobacilli
- palisades
- strephtobacilli
- club rod
- vibrio
- comma
Describe the cell wall structure of gram positive and gram negative bacteria.
+ve: thick peptidoglycan cell wall, one lipid bilayer
-ve: thin peptidoglycan layer in between two lipid bilayers (can have up to 40)
What was it found that arsenic-containing compounds helped cure? What was the compound called?
Syphilis infections
Organoarsenic compounds
What does magic bullet refer to?
Describes an ideal therapeutic agent, i.e. one that would only affect the target organism selectively. The more selectively toxic we can make a compound the greater the opportunity for application without side effects
How is DNA contained in the different types of microorganisms?
- Bacteria: bacterial chromosomes and plasmids
- Fungi: membrane bound nucleus containing chromosomes
- Protoazoa: micronucleus and macronucleus containing chromosomes
- Helminths: membrane bound nucleus containing chromosomes
- Algae: membrane bound nucleus containing chromosomes
What are the therapeutic methods are there for targeting bacteria?
- stopping genetic material replication
- restricting genetic material component availability
- compromising the structural integrity of the cell
- preventing synthesis of membranes needed for growth
- preventing synthesis of cellular proteins
Discuss the three main classes of biochemical reactions
Class I: target the production of metabolic precursors from substrates such as glucose, and therefore restrict any downstream processes.
Class II: target processes involved in the production of small molecules from metabolic precursors
Class III: target processes involved in the production of macromolecules from small molecule substrates
Antibacterial agents could also be classified how?
- Cell wall inhibitors
- bacterial cell membrane inhibitors
- bacterial protein synthesis inhibitors
- bacterial nucleic acid synthesis and action inhibitors
Name two nucleic acid synthesis inhibitors
PABA -> DHF inhibited by Sulfamethoxazole
DNF->THF inhibited by Trimethoprim
What does Ciprofloxacin do?
inhibition of DNA gyrase (gyrase: a bacterial enzyme that catalyzes the breaking and rejoining of bonds linking adjacent nucleotides in circular DNA to generate supercoiled DNA helices)
What does Rifampicin do?
it inhibits DNA-dependent RNA polymerase activity by forming a stable complex with the enzyme. It thus suppresses the initiation of RNA synthesis.
Name antibiotics that affect the ribosome (GETC)
Tetracyclin Gentamycin Eythromycin Chloramphenicol Fusidic acid
What is the peptidoglycan polymer made up of? How is it bonded?
N-acetylglucosamine (NAG/NAGA) and N-acetylmuramic acid (NAM/NAMA), bonded in an alternating pattern by beta-(1,4)glycosidic linkages
Describe the structure of peptidoglycan cell walls
The peptidoglycan polymers are crossed linked by short peptide chains that give rise to a mesh-like structure composed of repeating parallel peptidoglycan
What is the benefit of the cross-linked structure of bacterial cell walls?
Provides structural rigidity, while remaining porous, and preventing the cell from lysis under the osmotic pressure of the local environment
What amino acid is in the middle of the cross chain linking the peptidoglycan chains?
D-alanine and 2 other amino acids
How do Beta-lactam drugs work?
Covalently binding to the DD-transpeptidase enzymes that are responsible for cross-linking the peptides between peptidoglycan chains.
What beta-lactam compounds are there? (Please Can Ceara Make Cake)
- penicillin
- Cephalosporins
- Monobactams
- Carbapenems
- Clavulanic acid
What are the most common beta-lactam drugs
Penicillin
What does Vancomycin and related compound teichoplanin, do?
Prevent the synthesis of the bacterial cell wall by forming strong hydrogen bonds with the peptides that cross-link the peptidoglycan polymer chains, and thus prevent the formation of the normal lattice/mesh-like structure. Without cross-linking, the cell wall
integrity cannot be achieved, and therefore bacterial cell viability is compromised.
What does Vancomycin and related compound teichoplanin, do?
Prevent the synthesis of the bacterial cell wall by forming strong hydrogen bonds with the peptides that cross-link the peptidoglycan polymer chains, and thus prevent the formation of the normal lattice/mesh-like structure. Without cross-linking, the cell wall
integrity cannot be achieved, and therefore bacterial cell viability is compromised.
Name a bacterial cell membrane disruptor
daptomycin
How do bacterial cell membrane disruptors, such as daptomycin, work?
When multiple daptomycin molecules aggregate, their collective effect is to substantially distort the cell membrane shape, giving rise to holes. Loss of membrane integrity in this way causes depolarisation of the membrane, and consequently, chemical gradients necessary for many synthetic processes cannot be maintained. Ultimately, the bacterium dies though an inability to perform critical biochemical functions.
How do Polymixins work?
They compromise cell membrane integrity. They achieve their selectively for bacterial cells by binding to lipopolysaccharide (LPS) that is highly abundant in Gram-negative bacteria
Why aren’t Polymixins used very often?
Their treatment is often accompanied by a range of off-target effects that has limited their use, particularly since the development of agents with fewer associated toxicities.
What targets are used in bacterial cells to target protein synthesis?
70S ribosomes
What are prokaryotic ribosomes made up of?
30S and 50S
What are eukaryotic ribosomes made up of?
40S and 60S
What does S for ribosomes mean?
Sedimentation coefficient: the ratio of the rate of sedimentation of a particle to the centrifugal acceleration applied to it). In general, the bigger the molecule/particle, the great the coefficient value
What do the tetracyclines: Tetracycline, Doxycycline and Lymecycline work on? What is their common structural feature?
30S ribosome
Four connected and functionalised hydrocarbon rings
What do the aminoglycosides: Gentamycin, Neomycin, Tobramycin work on? What is their common structural feature?
30S ribosomes
Amino-modified glycoside
What do the macrolides: Erythromycin, Spiramycin, Telithromycin work on? What is their common structural feature?
50S ribosome
Macrocyclic lactone ring with one or more deoxy sugars
What does Chloramphenicol work on? What is its common structural feature?
50S ribosome
small molecule
What does Fusidic acid work on? What is its common structural feature?
50S ribosome
Small steroid
Synthesis of DNA and RNA in bacteria is dependent on the availability of?
Folic Acid
What precursor is folic acid synthesised from? What is this pathway called?
p-aminobenzoic acid (PABA): bacterial folate pathway
What enzymes are involved in the catalyzing the necessary biotransformation of folic acid precursors?
- dihydropteroate synthetase
- dihydrofolate reductase
How is synthesis of nucleic acids inhibited?
Competitive inhibition of the enzymes that synthesis the precursor of folic acid which is needed for nucleic acid synthesis
How is competitive inhibition of nucleic acids achieved?
Sulfonamides are structurally-similar to PABA (folic acid precursor), and trimethoprim is structurally similar to folic acid, and therefore introduction of these compounds will reduce the rate of bacterial DNA/RNA production and are bacteriostatic.
List the key components in the bacterial folate acid pathway
- Folate precursor p-aminobenzoic acid (PABA)
- dihydropteroate synthetase inhibitor: sulfamethoxazole
- Tetrahydrofolate (THF) precursor: dihydrofolic acid (DHF)
- Dihydrofolate reductase Inhibitor: trimethoprim
Bacterial DNA replication requires the action of what enzyme?
topoisomerase II
What is topoisomerase II otherwise known as?
bacterial DNA gyrase
Name some DNA gyrase inhibitors
quinolones such as ciprofloxacin, norfloxacin, and nalidixic acid
How do DNA gyrase inhibitors work?
Inhibition of this process prevents bacterial gene translation or replication, and consequently bacterial cell division. Inhibition of: catalysis of the breaking and rejoining of bonds linking adjacent nucleotides in circular DNA to generate supercoiled DNA helices.
Name a RNA synthesis inhibitor
rifampicin / rifampin
How does rifampicin / rifampin (RNA synthesis inhibitor) work?
Inhibits bacterial DNA-dependent RNA polymerase
- prevent normal bacterial function and growth
How can bacteria reduce the efficacy of antibacterial agents?
1) target modification
2) Immunity or bypass
3) Reducing the internal dose
4) Chemical inactivation
Describe bacteria’s ability to increase resistance by target modification?
Largely responsible for resistance is the change in the target of the antibacterial agent; in general, this means that critical biochemical interactions are no longer effective, and the drug cannot act.
Describe bacteria’s ability to increase resistance by immunity or bypass?
In some cases, the bacterial targets are not sufficiently well targeted or there is redundancy in the system (e.g. an enzyme may be inhibited, but the process is accomplished via another route).
Describe bacteria’s ability to increase resistance by Reducing the internal dose?
Efflux pumps can be expressed on the cell membrane to pump out the active agent.
Describe bacteria’s ability to increase resistance by Chemical inactivation?
Expression of enzymes or creation of an environment that inactivates a drug, or sequesters it.
What are the three main ways that bacteria display resistance to a given antibacterial agent?
- Inherent resistance of cells
- Mutation and selection of resistant cells
- Horizontal gene transfer to confer resistance mechanism on cells
Describe inherent resistance of bacterial cells
- existing degradation ability for the drug
- the cell is impervious to the drug
- the target is inaccessible and therefore cannot be acted upon
- they do not utilise the specific target / mechanism of the drug
Describe mutation and selection of resistant of bacterial cells
Variation in the population. Variation that leads to survival will be positively selected for if there is environmental pressure.
What will lead to increased antimicrobial resistance?
A key driver for antimicrobial resistance results from inadequate control of bacterial populations by antibiotics or low-level chronic exposure such as through routine animal treatment or incomplete/unnecessary use of antibiotics in therapy
What is the main/most common mechanism for antimicrobial resistance?
Horizontal gene transfer to confer resistance mechanism on cells
Describe how horizontal gene transfer to confer resistance mechanism on cells can occur
- Transformation through the uptake and incorporation of DNA containing a resistance gene
- Phage (virus) mediated transfer of a resistance gene
- Bacterial conjugation of a resistance gene
Define antimicrobials
A naturally - or synthetically - derived agent that inhibits or kills (one or more types of) microorganism
Define Antibiotic
Refers strictly to microorganism-produced substances that act against another microorganism
Define Antibacterial
A naturally - or synthetically - derived agent that inhibits or kills (one or more types of) bacteria
Define Bactericidal agent
An agent that kills bacteria
Define Bacteriostatic agent
An agent that prevents/arrests bacterial growth and/or reproduction without necessarily killing them
Define Commensal relationship
A symbiotic relationship between two organisms in which one benefits from the biological interactions while the other remains largely unaffected (no benefit or harm)
Define Horizontal gene transfer
The transfer of genetic material from one bacterium to another by either i) transduction of DNA; ii) phage-mediated transfer; iii) bacterial conjugation
Define Microbe
A microorganism
Define Mutualistic relationship
A symbiotic relationship between two organisms in which both benefit from the biological interaction
Define Vertical gene transfer
The transfer of genetic material from a parent to offspring
You should know the mechanism of action for…
Ciprofloxacin Penicillin Polymyxin Rifampicin Sulfamethoxazole Trimethoprim Vancomycin
Antimicrobial agents of most types have a wide therapeutic window (index) why?
They are highly selective for bacterial processes either qualitatively or quantitatively
What process does the antibacterial agent vancomycin inhibit?
Cell wall synthesis
Why might a poorly absorbed, low bioavailability drug be used?
Because the bacteria target are located in the gastrointestinal tract
What is Penicillin and how does it work?
- Small molecule antibiotic
- Covalently and irreversibly binds to DD-transpeptidase enzyme active site
- Prevents cross-linking of peptidoglycan in cell wall
What is Flucloxacillin and how does it work?
-Small molecule beta-lactam antimicrobial
- Inhibits penicillin-binding proteins that are responsible for peptidoglycan synthesis
- Prevents cell wall assembly
How does Polymyxin work and what is it?
- Peptide antimicrobial
- Disrupts cell membrane integrity
- Causes bacterial cell death
What is Rifampicin and how does it work?
- Medium-large heterocyclic compound
- Inhibits DNA-dependent RNA polymerase
- Prevents RNA synthesis, and therefore disrupts normal function and growth processes
What is Sulfamethoxazole and how does it work?
- PABA mimic
- Inhibits dihydropteroate synthetase
- Prevent synthesis of folate, a precursor in nucleic acid synthesis
What is Trimethoprim and how does it work?
- Folate mimic
- Inhibits dihydrofolate reductase
- Prevents synthesis of tetrahydrofolate, a precursor in nucleic acid synthesis
What is Vancomycin and how does it work?
- Glycopeptide
- Inhibits cross-linking of peptides between peptidoglycan polymer chains
- Prevents cell wall assembly
