Microbiology - Antimicrobial Agents 1 Flashcards
What 3 groups of antibiotics are classified as beta lactams?
Penicillins
Cephalosporins
Carbapenems
Name 2 glycopeptide antibiotics
Vancomycin
Teicoplanin
Describe the mechanism of action of beta lactams
Inhibits transpeptidase, which is an enzyme that forms cross links during the formation of the cell wall.
The resulting cell wall is therefore weak, and so the bacteria lyse because of osmotic pressure.
How does the cell wall of gram pos and gram neg bacteria differ?
Gram pos has thick peptidoglycan in cell wall
What bacteria is penicillin active against?
Gram positive
What bacteria is amoxicillin active against?
Broad spectrum: gram pos and many gram neg
Is streptococci gram pos or neg?
Gram pos
Which beta lactam antibiotic is effective against pseudomonas?
Piperacillin
How can beta lactam resistance be overcome? Give 2 examples of drugs?
Include a beta lactamase inhibitor
- Clavulanic acid + amoxicllin (in co-amoxiclav)
- Tazocin (piperacillin & tazobactam)
Is pseudomonas gram pos or gram neg?
Gram neg (Pseudo"moan"as - 'moan' = negative)
Is neisseria meningitis gram pos or gram neg?
Gram neg (Neisseria starts with N = negative)
Recall an antibiotic that is associated with C. difficile
Ceftriaxone (cephalosporin)
Which beta lactam antibiotics are used to treat to ESBL producing organisms?
Carbapenems
as ESBL producing organisms are resistant to cephalosporins
recall a caution of beta lactam antibiotic. do they cross the BBB?
Excreted renally so reduce dose if renal impairment
do not cross BBB
What type of bacteria are glycopeptides effective against?
Gram pos only - they are large molecules so can’t penetrate gram neg cell wall
What 2 infections are glycopeptides particularly useful for?
MRSA infection
C difficile
What is a caution of glycopeptide antibiotics?
They are nephrotoxic
Recall the broad mechanism of action of glycopeptide antibiotics
Prevent peptide cross links in cell wall
inhibit cell wall synthesis
Recall the broad mechanism of action of aminoglycosides
Bind to 30s ribosomal subunit, preventing elongation of polypeptide chain
(inhibit protein synthesis)
-bactericidal
Recall 2 examples of aminoglycoside antibiotics
gentamicin
amikacin
What type of bacteria are aminoglycoside antibiotics effective against?
Gram neg
Recall 2 toxicities of aminoglycosides
Ototoxicity
Nephrotoxicity
What type of bacteria are macrolides effective against?
Gram pos
What are macrolides particularly useful for?
Mild staph or strep infections in patients who are allergic to penicillin
Recall 3 macrolide antibiotics
Azithromycin
Clarithromycin
Eryhromycin
What type of bacteria are tetracylines effective against?
broad spectrum - intracellular organisms
Recall a class of antibiotic you should never give to children or pregnant women
Tetracyclines
Recall one side effect of tetracycline antibiotics
photosensitivity rash (summer effect)
Recall the broad mechanism of action of macrolides
Bind to the 50s subunit of ribosomes
bacteriostatic
Recall the broad mechanism of action of tetracyclines
Bind to 30s subunit of ribosomes
bacteriostatic
What type of bacteria is chloramphenicol effective against?
Many - it is v broad spectrum
Why is chloramphenicol rarely used?
Risk of aplastic anaemia and grey baby syndrome in neonates due to inability to metabolise drug
Recall 2 specific bacteria that macrolides are effective against
Campylobacter sp
Legionella pneumophila
Recall the broad mechanism of action of chloramphenicol
Binds to 50s subunit of ribosomes - inhibits formation of peptide bonds during translation
-bacteriostatic
Recall the broad mechanism of action of oxazolidinones
Binds to the 23s component of 50s subunit of ribosomes to prevent 70s subunit formation
Recall two types of bacteria that oxazolidinones are particularly active against
MRSA and VRE (vancomycin resistant enterococci)
Recall an example of oxazolidinones
Linezolid
Recall 2 potential side effects of oxazolidinones
Thrombocytopaenia & optic neuritis
Recall the broad mechanism of action of fluoroquinolones
Act on alpha subunit of DNA gyrase
(inhibit DNA synthesis)
- bactericidal
Recall 4 uses of fluoroquinolones
UTI
Pneumonia
Atypical pneumonia
Bacterial gastroenteritis
Recall 2 examples of fluoroquinolone antibiotics
Levofloxacin
Moxifloxacin
Give an example of a nitroimidazole antibiotic
Metronidazole
Recall types of organisms that metronidazole is effective against
Anaerobes
Protozoa
When should metronidazole be taken?
Right after visiting the toilet as it sits in bladder
Recall the broad mechanism of action of rifamycins
Binds to DNA-dependent RNA polymerase to inhibit RNA synthesis
example is rifampicin
Recall the main use of rifampicin
TB treatment
Recall one side effect of rifampicin
Turns secretions orange
Recall one condition of rifampicin prescription
Should never be prescribed alone as resistance develops very quickly
Colistin is very toxic. Why is it coming back into use?
It is active agianst certain multi-drug resistant bacteria
What is daptomycin licensed for the treatment of?
MRSA
VRE
Recall the 2 classes of antibiotic that inhibit folate synthesis
Sulphonamides
Diaminopyrimidines
Give an example of a sulphonamide
sulfamethoxazole
What is the main use of trimethoprim
Uncomplicated UTI
What are the 4 main mechanisms of resistance? Give examples
BEAT drug action
- Bypass antibiotic sensitive step in pathway e.g MRSA
- Enzyme mediated drug inactivation e.g beta lactamases
- Impairment of accumulation of the drug e.g tetracyclines
- Modification of the drugs target in the microbe e.g quinolone
Which antibiotic is best for treating pneumocystis jiroveci pneumonia?
this is a HIV defining disease
sulphamethoxazole + trimethoprim (co-trimoxazole)
What is the broad mechanism of action of nitroimidazoles?
Inhibit DNA synthesis
Which bacteria typically forms “gram pos cocci in clusters”?
Staphylococcus
Which bacteria typically forms “gram pos cocci in chains”?
Streptococcus
Strep sounds like ‘stripe’ = chain
What gram stain status are enterococci?
Positive
“Enter-o-coccus” = like letting someone in, positive thing to do
Is haemophilus gram pos or neg?
Gram neg
Ha”emo”philus - emo = negative
Is listeria gram pos or neg?
Positive
Lister = good man = positive
name 2 organisms that produce ESBL?
e coli
klebsiella pneumoniae
what 2 classes of antibiotics inhibit cell wall synthesis
beta-lactam antibiotics, glycopeptides
what 3 penicillins are broken down by beta-lactamase?
penicillin
amoxicillin
piperacillin
does ceftriaxone cover psueodmonas?
no
what type of bacteria is colistin used for? what’s a caution?
gram -ve
nephrotoxic and reserved for use against multi-resistant organisms
give an example of a diaminopyrimidine
trimethoprim
What 2 antibiotics classes inhibit cell wall synthesis?
beta-lactam antibiotics, glycopeptides
What 5 antibiotics classes inhibit protein synthesis?
aminoglycosdies tetracyclines macrolides chloramphenicol oxazolidiones
give 2 risks of chloramphenicol?
aplastic anaemia
grey baby syndrome - can’t metabolise drug
what 2 antibiotics classes are inhibitors of DNA synthesis?
fluroquinolones
nitroimidazoles
what drug class inhibits RNA synthesis?
rifamycin
what 2 antibiotic classes are cell membrane toxins?
daptomycin
colisitin
outline the gram staining procedure and results?
first step in gram staining is the use of crystal violet dye for the slide’s initial staining.
next step, also known as fixing the dye, involves using iodine to form crystal violet- iodine complex to prevent easy removal of dye.
finally, a decolorizer, often solvent of ethanol and acetone, is used to remove the dye.
If the bacteria stays purple, they are Gram-positive. If the bacteria turns pink or red, they are Gram-negative.
give an example of a tetracycline
doxycycline
who should not be given tetracylines and why
pregnancy women
growing children
deposits in bone and teeth
what antibiotic should you give as prophylaxis if someone is bitten?
co amoxiclav
what drug works best for MRSA
vancomycin
