Pathogen-Antibiotic Matching 1 Flashcards
How do gram positive bacteria stain? Why?
- Purple
- Due to thick peptidoglycan cell wall
- This takes up purple stain
- Due to this thick cell wall, it does not need an additional outer membrane
How do gram negative bacteria stain? Why?
- Pink
- Thinner peptidoglycan cell wall BUT has an additional outer membrane
- This membrane stops the crystal violet stain from penetrating the cell wall and hence does not become purple in response to the crystal violet stain
- Also due to the lack of peptidoglycan, meaning the stain cannot be retained
Describe cocci shape
Round - can be in pairs, chains or groups
Describe bacilli shape
Rods - groups, chains
gram positive/negative cocci/bacilli
Examples of classifications
What classification is S. aureus and S. epidermis?
Gram positive cocci
What classification is Strep pneumoniae and Strep pyogenese?
Gram positive cocci
What classification is clostridium difficile?
Gram positive bacilli
What classification is Listeria?
Gram-positive bacilli
What classification is Neisseria meningitides and Neisseria gonorrhoea?
Gram negative cocci
What classification is E. coli?
Gram negative bacilli
What classification is salmonella?
gram negative bacilli
What is the most common mechanism of antibiotics?
- Antibiotics that interfere with cell wall synthesis
- Prevent rigid cell wall from being assembled
- This includes the beta-lactams
- Prevent peptidoglycan from being incorporated into the cell wall
- Bacteria fall apart
What are the 2 main classes of antibiotics that inhibit cell wall synthesis?
- Beta-lactams:
- Penicillins: amoxicillin, penicillin V
- Cephalosporin: cefuroxime
- Carbapenem: meropenem
- Glycopeptides: vancomycin
Antibiotics can also target protein synthesis (translation), causing bacteria death. What are 4 important examples of these antibiotics?
- Tetracyclin (doxycycline)
- Macrolides (erythromycin)
- Chloramphenicol
- Aminoglycosides (gentamycin)
Antibiotics can also target RNA synthesis. Which antibiotic targets this?
Rifampicin
Antibiotics also target DNA replication. What are 3 examples of these?
- Quinolones (Ciprofloxacin)
- Metronidazole
- Anti-folates (folate is key in DNA replication)
- Trimethoprim
- Sulfa drugs
What are the 4 mechanisms by which antibiotics kill bacteria?
- Inhibit cell wall synthesis
- Inhibit protein synthesis/translation
- Inhibit RNA synthesis
- Inhibit DNA replication
All these targets are specific to bacteria - don’t harm human cell
What is the zone of inhibition? What is it used to measure?
- The Zone of inhibition is a circular area around the spot of the antibiotic in which the bacteria colonies do not grow
- Bigger zone = more effective antibiotic
- Can be used to measure the susceptibility of the bacteria to wards the antibiotic.
What are the 4 mechanisms of drug resistance? What are examples for each?
-
Drug inactivation or modification
-
Bacteria produce enzyme that destroys antibiotic
- Staph aureus –> penicillinase
- E. coli –> carbapenemase
-
Bacteria produce enzyme that destroys antibiotic
-
Alteration of target or binding site
-
Target of antibiotic changes shape so antibiotic can no longer bind and interfere with it
- Staph aureus –> alteration of penicillin binding protein
-
Target of antibiotic changes shape so antibiotic can no longer bind and interfere with it
-
Alteration of metabolic pathway
- Sulfa resistant bacteria can use pre-formed folic acid (instead of having to rely on making some)
-
Reduced drug accumulation
- Bacteria can express a drug pump in their cell membrane so antibiotics are pumped out of cell and back into environment and do not accumulate in cell
What type of antibiotic is Amoxicillin? Mechanism?
- Beta-lactam antibiotic, penicillin type
- Broad-spectrum activity against different types of infections caused by both Gram-positive and Gram-negative bacteria
- Mechanism: Inhibits cell wall synthesis
What is Amoxicillin used for?
ENT, respiratory and urinary infections
How can bacteria can resistance to Amoxicillin? What has been developed in response to this resistance?
- Produce B-lactamase enzymes which break down B-lactams
- Developed Co-Amoxiclav in response to this:
- Amoxicillin + clavulanic acid
- Clavulanic acid inhibits b-lactamase to help stop bacteria breaking down Amoxicillin
- Amoxicillin + clavulanic acid
- Co-Amoxiclav is therefore useful against B-lactamase producers
What is Tazocin a combination of?
Works same way as Co-Amoxiclav:
- Piperacillin (antibiotic) + Tazobactam (inhibits the action of bacterial β-lactamases)
What type of antibiotic is Flucloxacillin? Mechanism?
- B-lactam antibiotic
- Only active vs gram positive bacteria
- Mechanism: inhibits cell wall synthesis
- Bidns to penicillin binding protein
What is Flucloxacillin only active against?
Gram positive bacteria
What is Flucloxacillin mainly used to treat?
Staph aureus infections –> binds to penicillin binding protein
What is MRSA?
- Methicillin resistant S. aureus
- Has mutation in penicillin binding protein – resistance to fluclox
Can beta lactams be used to treat MRSA? What needs to be used instead?
- No due to mutation in penicillin binding protein
- Have to use other antibiotic class such as Vancomycin
Compare the spectrum of activity of:
- Penicillin
- Cephalosporins
- Carbapenems
Penicillin (Amoxicillin) < Cephalosporins (Cefuroxime) < Carbapenems (Meropenem)
e.g. Carbapenems are really broad spectrum
Clinical Case:
- 73 year old male is admitted with fever, cough shortness of breath and purulent sputum.
- He is confused, has a blood pressure of 80/55 and a respiration rate over 30
- What is diagnosis?
- What treatment would you start? Why?
- Pneumonia
- Co-amoxiclav + clarithromycin
- This is a systemic combination for community acquired pneumonia for someone who is very unwell
- Broad spectrum as not yet sure what pathogen is causing it
What score is used to calculate the severity of community-acquired pneumonia and, therefore, treatment?
- CURB-65 score
- Confusion
- Urea <7
- Respiration >30
- BP <90/60
- Age >65
What antibiotics are given to low risk pneumonia?
Amoxicillin
What antibiotics are given to high risk pneumonia?
Co-amox + clarithromycin
- What shape and gram-stain is this pathogen?
- If this pathogen is causing pneumonia, what is it likely to be?
- What antibiotic is used to treat this?
- Gram-positive cocci
- Streptococcus pneumoniae
- This is the most common cause of community acquired pneumonia
- Narrow spectrum penicillin (as Strep pneumo is sensitive to this)
- Fewer side effects compared to co-amox and clarithromycin
What pathogen is the most common cause of community acquired pneumonia?
Streptococcus pneumoniae
Which pathogen tends to cause hospital acquired pneumonia?
Klebsiella and other gram negatives
What antibiotic is used to treat pneumonia caused by Strep pneumoniae?
Penicillin
What is the relationship between side effects and the spectrum of an antibiotic?
Broad spectrum = more side effects
Clinical Case 1 Part 2
Your previous patient continues to be treated with co-amoxiclav and clarithromycin for 10 days (not switched to Amoxicillin). His chest improves. On day 10 he develops abdominal pain and green, watery diarrhoea.
- What is your diagnosis?
- How do you treat this?
- Clostridium difficile infection
- Gram-positive bacilli
- Common complication of broad spectrum antibiotic use
- Stop current antibiotics and start oral vancomycin
- As pneumonia has been cured
- Oral vancomycin is very targeted to C. difficile as stays in gut
What is a common side effect of broad spectrum antibiotic use? Why?
- Clostridium difficile infection
- Gut flora contains many bacteria which are all in competition with each other
- Broad spectrum antibiotics destroy a majority of species allowing a few to overgrow (Clostridium difficile)
- Clositridium difficile is a toxin producer –> colitis
Which broad spectrum antibiotics are most likely to lead to C. difficile infection?
Ciprofloxacin, cefuroxime, co-amoxiclav in elderly patients in particular
Clinical Case 2
A 20 year old woman presents to her GP with pain on urinating and frequent urination. She does not have a fever or any loin pain.
- What is your diagnosis?
- Lower urinary tract infection
How do lower UTIs present?
- Dysuria
- Frequency
- Sometimes pain when pressing bladder
What do lower UTIs involve the infection of?
Urethra and bladder
If bacteria migrate up the ureter and into the kidney from a lower UTI, this can lead to an upper UTI. How would patients present?
- Fever
- Loin pain
- Tachycardia
- Low blood pressure
This is a much more severe infection and can lead to sepsis
How would an upper UTI be treated?
- Broad spectrum antibiotics to start –> IV Cefuroxime
- Until you know which pathogen is causing it
How would a lower UTI be treated?
- Narrow spectrum antibiotic –> Nitrofurantoin, trimethoprim, pivmecillinam
What are the most common bacteria to cause UTIs?
- Gram negative bacillus:
- E. coli (most common)
- Proteus, Klebsiella
- Gram positive coccus:
- Staphylococcus saprophyticus
Who is Staphylococcus saprophyticus most likely to cause UTIs in?
Young sexually active females
Clinical Case 3
At the end of fresher’s week a 22 year old student starts feeling unwell. He develops a fever and becomes increasingly confused over the day. His friends ring an ambulance.
On admission he has neck stiffness and struggles with bright light (photophobia).
A cerebrospinal fluid sample shows the following.
- What is classification of pathogen
- What is the diagnosis?
- What pathogen has caused this?
- What is treatment for this?
- Round shaped, pairs –> diplococci
- Pink –> gram negative
- Meningitis caused Neisseria meningitides
- Gram negative cocci
- Treatment: IV broad spectrum antibiotic –> IV Ceftriaxone
How is meningitis treated?
- Broad spectrum antibiotic at first –> IV Ceftriaxone
- Narrow spectrum after pathogen has been found
Which bacteria typically causes meningitis in:
- Children and young adults?
- Elderly patients and neonates?
- N. meningitides
- Streptococcus pneumoniae
- Previously also Haemophilus influenza (now vaccinated)
If a patient with meningitis also presents with a non-blanching rash and was systemically unwell with low blood pressure and tachycardia, what would this be?
Meningococcal septicaemia:
- a bloodstream infection caused by Neisseria meningitidis
- the bacteria enter the bloodstream and multiply, damaging the walls of the blood vessels. This causes bleeding into the skin and organs.
Define sepsis
- Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection - a body’s response to an infection injures its own tissues and organs
- Organ dysfunction = change in SOFA score ≥2
What does sepsis cause?
- Drop in O2 conc
- Impaired coagulation with fall in platelets
- Liver dysfunction with rise in bilirubin
- Impairment of circulatory system with a fall in BP
- Mental impairment with a fall in the Glasgow Coma Scale
- Renal impairment with a rise in creatinine and a fall in urine output
Abbreviated SOFA score for sepsis:
- Low BP
- High respiratory rate
- Altered mental state
Managment of SEPSIS –> BUFALO
- Blood cultures: 2 sets
- Urine output: Patient catherised to measure urine output
- Fluids: 500ml IV saline over 15 minutes. Aim 30ml/kg in 1 hour.
- Antibiotics: As per suspected infection
- Lactate: Arterial blood gas for lactate and pH
- Oxygen: 15 l/min via reservoir face mask
What fluids are given in suspected sepsis? Why?
- 500ml IV saline over 15 minutes
- Aim 30 ml/kg in 1 hour
- The body needs extra fluids to help keep the blood pressure from dropping dangerously low, causing shock
- The fluid is called isotonic, as it does not change the size of the cells.
Clinical Case 4
A 50 year old man sustains a skin scrape while working in the garden. Over the next few days develops the following picture and he has a fever:
Cellulitis
What is cellulitis? How does it present?
- Skin and soft tissue infection
- Bacterial
- The bacteria can infect the deeper layers of your skin if it’s broken – for example, because of an insect bite or cut, or if it’s cracked and dry.
- The affected skin appears swollen and red and is typically painful and warm to the touch.
What bacteria is cellulitis caused by? How is it treated?
- Gram positive cocci e.g. Staph aureus and Step pyogenes
- Treated with Flucloxacillin
What is necrotising fascitis? Which bacteria typically causes it? What is the treatment?
- A severe skin and soft tissue infection caused by a polymicrobial mix, but usually involving Streptococcus pyogenes.
- Treatment:
- Debridement: removing all infected tissue
- Meropenem + clindamycin
- Meropenem: carbapenem-type antibiotic
- Clindamycin: is active against Gram-positive cocci, including streptococci and penicillin-resistant staphylococci, and many anaerobes.
Clinical Case 5
A 25 year old PWID (person who injects drugs) is admitted with a 2 week history of fever, night sweats and shortness of breath.
He has a heart murmur on auscultation.
- What is your top differential?
- Infective endocarditis
- Bacteria has been introduced straight into bloodstream via needle
- N.B. PWID are also at high risk of blood borne viruses (e.g. HIV, hep B, hep C) so also need to screen for these
What is infective endocarditis? What pathogens typically cause it? What is treatment?
- Infection of heart valves
- Many possible pathogens but most common:
- Staph aureus
- Streptococci
- ~6 weeks IV antibiotics depending on bacteria
Why are PWID most at risk of infective endocarditis caused by bacteria that live on your skin?
As needle penetrates skin, it takes bacteria along with it into the blood which can then settle on your valves: Staph aureus and Streptococci
Which antibiotics are the most well tolerated and safe in pregnancy?
Beta lactams: penicillins and cephalosporins
Which antibiotics should be avoided/limited use in pregnancy? What damage can each of these do?
- Quinolones (ciprofloxacin) – damage to cartilage
- Trimethoprim – folic acid antagonist
- Most important to avoid in 1st trimester
- Tetracyclins – deposits and stains bones/teeth
