Bacteriology - General structure & AMR Flashcards
What are the main methods of antibiotic actions?
- Inhibition of cell wall synthesis
- Inhibition of protein synthesis
- Inhibition of nucleic acid synthesis
- Anti-metabolites
How many AMR be mediated?
- chromosome-mediated
- plasmid-mediated
- transposon-mediated
Describe chromosome-mediated resistance
- due to mutation in gene that codes for the target of the drug, or the transport system in the membrane that controls uptake
Why is plasmid-mediated resistance clinically important?
- occurs in many different species
- plasmids frequently mediate resistance to multiple drugs
plasmids have a high rate of transfer
What are transposons?
Genes that are transferred either within or between larger pieces of DNA, such as the bacterial chromosome, and plasmids
What is a typical drug-resistance transposon composed of?
3 genes, flanked by shorter pieces of DNA - the genes code for…
- transposase (enzyme that catalyses the excision and reintegration of the transposon)
- a repressor that regulates synthesis of the transposase
- the drug resistance gene
What is vertical gene transfer?
Occurs through replication
What are the three methods of HGT?
- Conjugation
- Transduction
- Transformation
What is conjugation?
between two bacterial cells in direct contact
What is transduction?
Injection of foreign DA into the host bacterium by a bacteriophage virus
What is transformation?
Uptake of naked genetic material fragments through cell membranes, recombined with bacterial chromosome of the recipient
The transfer of antibiotic resistance genes from one strain of bacterium to another via a virus is called
transduction
The transfer of antibiotic resistance genes from one strain of bacterium to another via uptake of nakedDNA is called
transformation
What are the five main mechanisms that mediate bacterial resistance to drugs?
1 - production of enzymes that inactivate the drug
2 - synthesis of modified targets against which the drug has reduced effect
3- reducing permeability to the drug such that an effective intracellular concentration of the drug is not achieved
4 - actively export drugs using a ‘multidrug resistance’ pump which imports proteins in exchange for a variety of foreign molecules, including antibiotics
5 - target amplification
What are the major categories of antibiotics?
- cell wall inhibitors
- protein synthesis inhibitors
- nucleic acid synthesis inhibitors
What are the main types of cell wall inhibitors
- beta lactams
- vancomycin
- isoniazid
Give examples of beta lactams
- penicillin
- amoxicillin
- benzylpenicillin
- flucloxacillin
- cephalosporins
How do beta lactams work?
They irreversibly inhibit transpeptidase, causing osmotic rupture of the bacteria
How does vancomycin work?
Prevents transpeptidase from binding and catalysing cross-link formation
How does isoniazid work?
Inhibits synthesis of long chain mycolic acids required for bacterial wall and capsule
The most common mechanism of resistance to penicillin and cephalosporin antibiotics found inantibiotic resistant strains of bacteria is
beta-lactamases (but also altered penicillin-binding proteins and decreased permeability via GNB efflux)
What two classes of antibiotic affect the 30S subunit?
Aminoglycosides
Tetracyclines
What do aminoglycosides do?
Bind to 30S so it cannot bind with 50S and an mRNA for form the initiation complex
What do tetracyclines do?
Bind to 30S, preventing aminoacyl-tRNAs from entering the donor site in the ribosome
Example of aminoglycosides
streptomycin
gentamycin
tetracycline
Example of tetracycline antibiotic
Doxycycline