Antibiotics Flashcards
What is an antibiotic?
Antibiotics are molecules that work by binding a target site on a bacteria
what class of antibiotic is penicillin
B lactam
List some B lactam antibiotics
penicillin derivatives
cephalosporins and cephamycins
monobactams
carbapenems and carbacephems
what does the antibiotic polymyxin work on
Cell Membrane
Treats gram negative infections, last line of antibiotics, narrow spec
What are the classes of antibiotics that work on 30s
Tetracyclines
Aminoglycosides
What are the classes of antibiotics that work on 50s
Macrolides
Clindamycin
Linezolid
Chloramphenacol
Streptogramins
what are the classes of antibiotics that work on RNA polymerase
Rifampin
What are the classes of antibiotics that work on DNA gyrase
Quinolones
What are the classes of antibiotics that work on folalte synthesis
Sulfonamides
Trimethoprin
What type of antibiotics are Vancomycin +
Teicoplanin
Glycopeptides
Treat beta lactam resistant gram +ve bacteria
Describe how Beta lactam antibiotics
work
- disrupt peptidoglycan production
- bind covalently and irreversibly to Penicillin Binding Proteins (PBP’s)
- To bind to the PBPs, the β-lactam antibiotic must first diffuse through bacterial cell wall
- Gram -ve have an LPS layer that decreases antibiotic penetration
- cell wall is disrupted and lysis occurs
- results in a hypo-osmotic or iso-osmotic
- Active only against rapidly multiplying organisms
- Differences in broad vs narrow spectrum are due to affinity for PBPs
gram +ve more susceptible to β-lactams than gram-negative bacteria
Briefly describe what a bactericidal antibiotic is
- Kills 99.99% bacteria
- Inhibits cells wall synthesis
-usually beta lactams
-good for needing to get rid of bacteria quickly (meningitis)
Briefly describe what a bacteriostatic antibiotic is
*inhibit growth
*Inhibit protein synthesis, DNA replication or metabolism
How do bacteria become resistant to Penicillins and cephalosproins
Both types of antibiotic contain a beta lactam ring
Beta-lactamase hydrolysis this ring and the antibiotic and now unable to bing to the PBP’s
Why do bacteria develop resistance?
*Intrinsic - Naturally resistant
*Extrinsic - Naturally acquired through spontaneous gene mutation or horizontal gene transfer (conjunction, transduction, transformation)
what are the two major determinants of anti bacterial effects
concentration and the time
Describe intrinsic bacterial resistance.
D
Briefly describe Horizontal gene transfer: Transduction with and example.
*Insertion of DNA by bacteriophages
*mecA genes for MRSA
Briefly describe horizontal gene transfer: Conjugation and and example.
*Sharing of extra chromosomal DNA plasmids
*New Delhi metallo-B-lactamase
Briefly describe horizontal gene transfer: Transformation and example
*foreign DNA from S. mitis to S. pneumoniae, conferring penicillin resistance
What does MRSA stand for
Methicillin resistant Staphylococcus aureus
What is MRSA resistant to
resistance to all β-lactam antibiotics in addition to methicillin
what does VRE stand for
vancomycin-resistant enterococci
How did MRSA become resistant to antibiotics
- transduction - Bacteriophage mediated acquisition of Staphylococcal cassette chromosome mec (SCCmec)
containing resistance gene mecA
*encodes penicillin-binding protein 2a (PBP2a)
How did VRE become resistant to antibiotics
*Plasmid-mediated acquisition of gene encoding altered amino acid on peptide chain preventing vancomycin binding
*Promoted by cephalosporin use
What gram is MRSA
+VE
What gram is VRE
+ve
What gram is ESBL
-VE
What does ESBL stand for
extended spectrum beta lactamase (ESBL)
what gram bacteria do Vancomycin and Teicoplanin treat
+ve only
whe should you use vancomycin and teicoplanin?
*Gram-positive bacteria resistant to beta-lactams
*when the patient is allergic to penicillin
which classes of antibiotics work on cell wall synthesis
B lactams
Vancomycin
Bacitracin
Which classes of antibiotics work on nucleic acid synthesis
*Rifampin working on RNA pol
*Quinolones working on DNA gry
*Sulfonamides Trimethoprin working onFolate synthesis
what cells can beta-lactams not enter?
*Eukaryotic cell
Beta lactams arent so useful for bacteria that can enter euk cells
which antibiotics work on protein synthesis
*Tetracyclines and aminoglycosides working on 30s
*macrolides clindamycin etc working on 50s
what are some consequences (bodily) of antibiotics
Direct- destroy phagocytes cells which bacteria replicate
Indirect - inflammation
Diarrhoea
Toxins- exotoxin (protein product) and endotoxin ( gr -ve)
The amount of antibiotic needed is called …..
minimum inhibitor conc (MIC)
what is used to treat staph aurious
Flucloxacillin
why cannot vancomyocin treat gram negative
Cannoy penetrate the cell membrane.
what are some things to consider when prescribing antibiotics
*Drug interactions
*risk of c diff
*pregnancy
*Allergies
*age
*Renal and liver function
gram +ve and catalyse +ve =
Staph coccus
gram +ve and Catalase -ve =
Strep coccus
Streptococcus when undergoing haemolysis on blood agar if beta will be …..
Group A C G
Streptococcus when undergoing haemolysis on blood agar if alpha will be …..
tested with optochin and if sensitive will be Streptococcus pneumoniae
What are A C G groups of s. aurius
Flucloxacillin
Why cant you treat a CNS infection with vancomycin
Vancomycin does not effectively cross the blood-brain barrier.
what could you use to treat necrotizing facsch
Clindamycin
which gram negative use lactose as a food source
Klebs, e.coli
