Antibiotics Flashcards
How are bacteria classified?
They are stained and looked at
What is the difference in structure between a gram positive and gram negative bacteria?
Gram positive:
- has a peptidoglycan cell wall
- stains purple with gram stain
Gram negative:
- the outermost layer is the outer cell membrane
- the cell wall is protected in the middle
- stains pink with gram stain
What are the 2 shapes of bacteria?
Cocci:
- these are round in shape
- in pairs, chains or groups
Rods:
- these are elongated
- in groups, chains or solo
Complete the table showing the results of the Gram stain and further tests
WHy is the catalase test used?
To distinguish between staphylococcus and streptococcus
these are both gram positive cocci
How do b-lactams work?
B-lactams are a group of antibiotics which all contain the b-lactam group
they are cell wall synthesis inhibitors
What are the 4 types of b-lactams?
Penicillins:
- amoxicillin
- penicillin V
Cephalosporin:
- cefuroxime
Carbapenem:
- Meropenem
Glycopeptides:
- vancomycin
What are the 4 antibiotics which interfere with translation (protein synthesis)?
- Tetracyclin (doxycycline)
- Macrolides (erythromycin)
- Chloramphenicol
- Aminoglycosides (gentamycin)
The shape and composition of the bacterial ribosome is different so it can be exploited through antibiotic use
Which antibiotic interferes with RNA synthesis?
Rifamycin (rifampicin)
Which antibiotics interfere with DNA replication?
Quinolones:
- ciprofloxacin
Metronidazole
- used in anaerobic infections
Anti-folates:
- trimethoprim
- sulfadrugs
- folate is needed for nucleotide synthesis, so bacteria are prevented from making DNA
What are the 4 mechanisms of drug resistance?
- Drug inactivation or modification
- Alteration of target or binding site
- Alteration of metabolic pathway
- Reduced drug accumulation
How does “drug inactivation or modification” work as a mechanism of resistance?
Bacteria produce an enzyme that will break down the antibiotic
staphylococcus aureus produces penicillinase
e. Coli produces carbapenemase
How does “alteration of target” work as a mechanism of resistance?
Antibiotics have to bind to something (e.g. cell wall, ribosome)
bacteria may have evolved a binding site that is different so that the antibiotic can no longer bind to its target site
staphylococcus aureus alters the penicillin binding protein
How does “alteration of metabolic pathway” work as a mechanism of drug resistance?
Sulfa-resistant bugs can use pre-formed folic acid
e.g. Trimethoprim inhibits the folate pathway of bacteria
enterococcus will use folate from the blood surrounding it instead
How does “reduced drug accumulation” work as a mechanism of drug resistance?
This involves actively pumping out the antibiotic that is penetrating into the cell
“efflux pump”
Which types of bacteria are resistant to amoxicillin?
Which infections is it used against?
- Most beta lactams have some gram positive and gram negative activity
- amoxicillin is used for ENT, respiratory and urinary infections
- bacteria with B-lactamase will break down B-lactams
What is used to overcome bacteria that produce B-lactamase?
Co-amoxiclav
this is a combination of amoxicillin and clavulanic acid
it is used against beta-lactamase producing bacteria
How does flucloxacillin work?
What types of bacteria are they used against?
It inhibits cell wall synthesis and binds to penicillin binding protein
it is mainly used to treat staphylococcus aureus infections
it is only active against gram positive bacteria
What does MRSA stand for?
Why is it resistant to flucloxacillin?
Methicillin resistant S aureus
it has a mutation in the penicillin binding protein so is resistant flucloxacillin
What is the difference between MRSA and staphylococcus aureus?
It has an extra resistant disease that gives resistance to methicillin
This means that beta-lactams can’t be used to treat MRSA
another antibiotic class needs to be used (vancomycin)
What is the antibiotic treatment for community acquired pneumonia?
How is this worked out?
Use the CURB65 score
confusion, urea >7, respiration > 30, BP < 90/60, age > 65
in LOW risk pneumonia - amoxicillin
in HIGH risk pneumonia - co-amoxiclav + clarithromycin
What is shown on the blood culture?
Gram positive coccus - diplococci
this is streptococcus pneumoniae
What is the most common cause of community acquired pneumonia?
Streptococcus pneumoniae
klebsiella and other gram negative bacteria are commoner in hospital acquired pneumonia
What is the best treatment for community acquired penicillin caused by streptococcus pneumoniae?
Streptococcus pneumoniae is sensitive to penicillin
this has fewer side effects compared to co-amoxicillin and clarithromycin
these are broader spectrum antibiotics
Why should a broad spectrum antibiotic not be used in long term?
Broad spectrum antibiotics cover a wide range of bacteria, some of which are not causing a problem
the best treatment is the most targeted treatment as you only want to kill the bacteria that is causing the problem
What bacteria is shown here?
How is infection often contracted?
Clostridium difficile
a long course of broad spectrum antibiotic wipes out all the “good” bacteria
C. Difficile will overcrowd the gut as there is less competition
How is C. Difficile infection contracted?
- Gut flora contains many bacteria
- these are all in competition with each other
- broad spectrum antibiotics destroy a majority of species allowing a few to overgrow
- clostridium difficile is a toxin producer - colitis
What are the worst antibiotics for inducing C. Difficile infection?
Ciprofloxacin, cerfuroxime, co-amoxiclav
worse in elderly patients
How is C. Difficile infection treated?
Stop current antibiotics (broad spectrum) and start oral metronidazole
What is the difference in symptoms for an upper and lower urinary tract infection?
Upper urinary tract infection:
- fever
- loin pain
- tachycardia
- low blood pressure
Lower urinary tract infection:
- dysuria
- frequency
What drugs are used to treat upper and lower urinary tract infections?
Upper urinary tract infections:
- IV cerfuroxime
Lower urinary tract infections:
- nitrofurantoin
- trimethoprim
- pivmecillnam
What bacteria commonly cause UTIs?
70% of all UTIs are caused by E. coli
What is shown here?
Gram negative coccus
It is meningitis caused by Neisseria meningitides
What is the treatment for meningitis caused Neisseria meningitides?
IV ceftriaxone
What is meningitis?
What is it caused by?
It is an infection of the meninges
In children and young adults it is caused by N. Meningitides
In elderly patients it is caused by Streptococcus pneumoniae
It was previously also caused by Haemophilus influenza, but this is now vaccinated
What is the difference between meningitis and meningococcal septicaemia?
Meningitis affects the CNS only
Meningococcal septicaemia is a CNS and bloodstream infection
What is the definition of systemic inflammatory response syndrome (SIRS)?
2 of the following must be present:
- temperature > 38
- heart rate > 90
- resp rate > 20
- White blood cells > 12
What is the definition of sepsis?
SIRS and a suspected focus of infection
What is the definition of septic shock?
Sepsis and a low blood pressure ( < 90 / 60 )
What technique is used in the management of sepsis?
BUFALO
Blood cultures:
- 2 sets should be taken
Urine output:
- catheterise to measure
Fluids:
- 500 ml IV saline over 15 minutes
- aim for 30 ml/kg in 1 hour
Antibiotics:
- start with a broad spectrum antibiotic until you know what is causing the infection
- then use as per suspected infection
Lactate:
- arterial blood gas for lactate and pH
Oxygen:
- 15 l/min via reservoir face mask
What is cellulitis?
What is it caused by?
It is a skin and soft tissue infection
It is caused by gram positive cocci - staphylococcus aureus AND streptococcus pyogenes
S. Aureus is found on the skin and doesn’t usually cause problems, but trauma to the skin can lead to the bacteria entering the tissue and causing an infection there
What is the treatment for cellulitis?
Flucoloxacilln
What can happen if cellulitis is left untreated?
What causes this infection?
Necrotising fasciitis
this is a severe skin and soft tissue infection caused by a polymicrobial mix
it usually involves streptococcus pyogenes, which is a potent pathogen
What is the treatment for necrotising fasciitis?
1 - debridement:
- this involves cutting away dead skin
- dead skin is not penetrated by antibiotics as there is no blood flowing through it
2 - meropenem + clindamycin
What is shown here?
What condition is it associated with?
Splinter haemorrhages
associated with infective endocarditis
small emboli break away from the heart valves and lodge in small capillaries
What is infective endocarditis?
What is it caused by?
It is an infection of the heart valves
it can be caused by many bacteria but mainly:
- Staphylococcus aureus
- Streptococci
What is the treatment for infective endocarditis?
6 week IV antibiotics, depending on the cause
it is difficult to remove the bacteria from the heart valves as they form a biofilm
What is shown on this image?
What predispositions could make someone more susceptible?
Brain abscess
- Immunosuppression
- HIV
- Intravenous drug use
- Endocarditis
What are the most common bacteria that cause brain abscess?
What is the treatment?
Staphylococcus aureus and streps
but it can be caused by anything
it is treated with drainage and antibiotics for 4 weeks, depending on the bug
What are the most well tolerated antibiotics in pregnancy?
Beta-lactams
these are the most well tolerated antibiotics and safe in pregnancy
penicillins, cephalosporins, meropenem
Which 3 antibiotics should be avoided in pregnancy and why?
Quinolones:
- e.g. ciprofloxacin
- they cause damage to cartilage
Trimethoprim:
- this is a folic acid antagonist
Tetracyclins:
- depositis and stains bones and teeth
