9 antibacterials Flashcards
What substance is an antibiotic ?
a low molecular substance produced by a microorganism
Definition of antimicrbial = chemical that …
kills or inhibits the growth of micro-organisms
antibiotic = chemical …..
produced by micro-organism that kills or inhibits the growth of another micro-organism
chemotherapy is what ?
a chemical-based treatment for diseases caused by micro-organisms and tumour cells
what are naturally occurring antimicrobials ?
- metabolic products of bacteria and fungi
- reduce competition for nutrients and space
2 examples of antibiotics produced by bacteria
- streptomyces
- bacillus
2 examples of antibiotics produced by mould ?
- penicillium
- cepahosporin
what are the 3 mode of actions of antimicrobials ?
- bacteriostatic
- bacteriocidal
- bacteriolytic
Features of bacteriolytic mode of action
- kills bacterial cells
- lysis of bacterial cells
- irreversible
features of bacteriostatic mode of action
- Inhibit or delay bacterial growth & replication
- non-lethal
- reversible
3 examples of antibacterials with bacteriostatic mode of action
- tetracycline
- chloramphenicol
- erythromycin
features of bacteriocidal mode of action
- kills bacterial cells
- irreversible
4 examples of bactericidal mode of action antibacterials
- cephalosporins
- penicillins
- aminoglycosides
- co-trimoxazole
at a low concentration what can an antibiotic do ?
inhibits or kills other microorganisms
What is an antimicrobial ?
substance of natural, semisynthetic or synthetic origin that kills or inhibits the growth of microorganisms but causes little or no damage to the host
what’s the relationship between antibiotics and antimirobials ?
All antibiotics are antimicrobials, but not all antimicrobials are antibiotics
What do bacteriostatic drugs do ?
inhibit or delay bacterial growth and replication
Who are bacteriostatic antibiotics not advisable for use in ?
- immunosuppressed or immunocompromised conditions
- those suffering from life-threatening acute infections
Why are bacteriostatic antibiotics not advisable for use in immunosuppressed or immunocompromised conditions and those suffering from life-threatening acute infections ?
onset of action for bacteriostatic agents is generally slower than that of bactericidal agents
bacteriostatic drugs require a working immune system for effective elimination of the microorganism by the infected host
Depending what can antibiotics be both bacteriostatic and bactericidal ?
- dose
- duration of exposure
- state of the invading bacteria
how are antibacterials classified ?
- mode - bacteriostatic , bacteriocidal, bacteriolytic
- structure - e.g. beta-lactam structure, aminoglycosides structure
- spectrum - narrow, extended, broad
- mechanism - 6 mechanisms (4 inhibit, 1 blocks, 1 disrupt)
What do antibiotics within a structural class usually have ?
similar mode of action , spectrum of activity and toxicity
- narrow spectrum antibiotics act on ?
- two examples name
- single or limited group
- isoniazid only active against and mycobacteria
extended spectrum bacteria act on ? & example
act in GP and a significant number of GN bacteria
ampicillin
broad spectrum antimicrobials act on ? & example
wide variety of microbial species
* tetracycline
* chloramphenicol
what are 6 mechanisms of action that drugs have ?
dirupt unique components of the cytoplasmic membrane
block a pathogens recognition of or attachment to its host
inhibit:
* cell wall synthesis
* protein synthesis
* general metabolic pathways not used by humans
* nucleic acid synthesis
What can drugs that target cell walls do to bacterial organisms ?
selectively kill or inhibit
To enlarge or divide a bacterial cell what must be done ?
synthesise peptidoglycan by adding new N-acetylglucosamine and N-actyymuramic acid
what do many drugs that inhibit cell wall synthesis do ?
prevent the cross linking of the NAM subunits by inhibiting transpeptidase enzymes
peptidoglycan synthesised by adding new N-acetylglucosamine and N-actyymuramic acid
e.g. penicillin
What are beta lactam antibiotics characterised by ?
4 membered, nitrogen containing beta-lactam ring at core of its structure
What do the drugs that inhibit cell wall synthesis inhibit ?
the cell wall formation by binding to transamidase (penicillin binding protein), this binding inhibit the enzyme from cross linking the peptidoglycan monomers which result in weak and fragile cell wall
What do beta lactam antibiotics target ?
- Penicillin Binding Proteins = transamidase (PBPs) Role: PBPs are crucial for bacterial cell wall synthesis as they cross-link the cell wall components.
- Beta-Lactam Antibiotics Mechanism: The beta-lactam ring in these antibiotics binds to PBPs.
- Inhibition of PBPs: This binding prevents PBPs from cross-linking the cell wall.
- Resulting Effect on Bacteria: The disruption in cell wall synthesis causes bacterial cell death due to osmotic instability or autolysis.
what mode of actions are beta lactam antibiotics ?
generally bactericidal
4 examples of beta lactams
- penicillin
- cephalosporins
- carbapenems
- monobactams
what are beta lactamases ?
destroy the beta-lactam ring
How do prokaryotic ribosomes differ from eukaryotic ribosomes in both structure an size ?
prokaryotic: 30S , 50S
eukaryotic: 80S, 60S & 40S
Many antibacterial agents bind to either the 30S or 50S subunity of the intracellular ribosomes causing what ?
disruption of the normal cellular metabolism of the bacteria, leading to the death of the organism of the inhibition of its growth and multiplication
6 examples of drugs that inhibit protein synthesis :
CT SLAM
- Chloramphenicol
- Tetracyclines
- Streptogramins
- Aminoglycosides
- Macrolides
What’s the difference between what the following protein synthesis inhibitors bind to : tetracyclines, aminoglycosides, macrolides and chloramphenicol ?
tetracyclines & aminoglycosides bind to 30S subunits
macrolides & chloramphenicol bind to 50S subunit, halting protein synthesis
Once inside the bacteria cell, what do ainoglycosides do ?
bind to 30s ribosomal sub-unit and cause a misreading of the genetic code
leading to interruption of normal bacterial protein synthesis
What does chloramphenicol irreverisbly bind to ?
a receptor site on the 50S subunit of the bacterial ribosome inhibiting peptidyl transferase
Inhibition of peptidyl transferase by chloramphenicol results in what ? leading to …?
results in prevention of amino acid transfer to growing peptide chains, leading to inhibition of protein formation
What happens after tetracyclines have been transported into the cell ?
they reversibly bind to receptors on the 30S ribosomal subunit of the bacteria, preventing attachment of aminoacyl-tRNA to the RNA-ribosome complex
preventing addition of amino acids to the elongating peptide chain , preventing synthesis of proteins
protein synthesis inhibitor mechanism ?
Nucleic acid synthesis inhibitors ?
- topoisomerase IV
- DNA gyrase
action of topoisomerase IV ?
unlinks DNA after replication
[change Q] action of DNA gyrase & topoisomerase IV?
involved in relaxation of super-coiled DNA - step required for normal transcription and duplicaiton
Some antibiotics work by binding to components involved in the process of DNA replication or RNA transcription
what does this cause interference of …?
the normal cellular processes which will ultimately compromise bacterial multiplication and survival
3 examples of drugs that inhibit nucleic acid synthesis
- quinolones
- metronidazole
- rifampin
Drugs that block a pathogen recognition of or attachment to its host:
Some new ..1.. block the attachment of microbes, especially ..2.., to the host cells using attachment …3…. Using peptide and sugar analogues the ..4… can neither attach nor …..5…. a cell.
- antimicrobial agents
- viruses
- analogues
- viruses
- enter
Why is the action of antibiotics that disrupt the cytoplasmic membrane often poorly selective and can often be toxic for systemic use in the mammalian host ?
the structures is found in both eukaryotic and prokaryotic cells
Drugs that disrupt unique components of the cytoplasmic membrane have a clinical usage that is limited to what applications ?
topical
Give an example of a drug that disrupts the unique components of the cytoplasmic membrane
polymixin B
- What do both sulfonamides and trimethoprim disrupt ?
- why is this step that these antbiotics disrupt necessary for bacteria ?
- folic acid pathway
- to produce precursors important for DNA synthesis
What are the 2 enzymes that are essential for the production of folic acid (a vitamin synthesised by bacteria) but not humans?
- dihysropteroate synthase
- dihydrofolate reductase
What does sulfonamide compete with in bacteria thereby inhibiting the synthesis of wha?
competes with PABA (p-Aminobenzoic acid) which is required by bacteria to synthesise folate, by competing with this it thereby inhibits the synthesis of dihydrofolic acid
2 examples of antbiotics that are sulfonamides
- sulphamethoxazole
- co-trimoxazole
what does trimethophrim inhibit in bacteria ?
dihydrofolate reductase
