Theme 3 Lecture 17, 19, 20: Pathogen-antibiotic matching Flashcards
Why do gram-positive bacteria stain dark purple?
because the carbohydrate rich cell wall on outside takes up purple dye
Why do gram negative bacteria stain pink?
because the outer cell membrane prevents the dye from penetrating the peptidoglycan
Other than gram stain, how else can we classify bacteria?
by shape:
- cocci - in pairs, chains or groups
- bacilli (rods) - in chains, groups or solo
what is the shape of streptococci?
chains of cocci e.g strep pneumoniae
What is the shape of staphylococci?
bunches of cocci e.g staph aureus
What do the most widely used antibiotics interfere with?
cell wall synthesis e.g b-lactams and glycopeptides
What are the 4 different mechanisms by which antibiotics can develop resistance?
- Drug inactivation or modification
- drug produces an enzyme that destroys the antibiotic - alteration of target - or binding site
- target of antibiotic can change shape so the antibiotic can no longer bind - alteration of metabolic pathway
- reduced drug accumulation
- drugs are pumped out of cell and back into environment
What is amoxicillin and what is it commonly used for?
- very commonly used B-lactam (inhibits cell wall synthesis of bacteria)
- used for ENT, respiratory and urinary infections
What is B-lactamase?
resistant enzyme that breaks down B-lactams
What is co-amoxiclav?
- amoxicillin+ clavulanic acid
- useful against beta-lactamase as clavulanic acid inhibits B-lactamase so it cannot break down
How does flucloxacillin work and what is it used for?
- inhibits cell wall synthesis
- B-lactam
- only active against gram +ve
- mainly used to treat staph aureus infections
- binds to penicillin binding proteins
Why can Beta lactams not be used to treat MRSA?
MRSA = methicillin resistant S.aureus
- has a mutation in PBPs - resistant to flucoxacillin
- have to use other antibiotic class e.g vancomycin
What are the 3 types of B-lactams in order from the broadest spectrum to narrowest spectrum?
- carbapenems (broad spectrum)
- cephalosporins
- penicillin (narrower spectrum)
What does purulent mean?
pus containing
what is the treatment for a high risk patient with community acquired pneumonia?
co-amoxiclav and clarithromycin
what is the treatment for a low risk patient with CAP?
Amoxicillin
What is the most common cause of community acquired pneumonia?
streptococcus pneumoniae
What are the common causes of hospital acquired pneumonia?
klebsiella pneumoniae and other gram -ve
What is a common complication of broad spectrum antibiotic use?
C.difficile
How do you treat C.difficule?
stop current antibiotics and start oral vancomycin - very targeted for C.difficile as it is absorbed by the gut
What are the symptoms of lower urinary tract infection?
- dysuria
- frequency (increased urination)
What are the symptoms of upper UTI?
- fever
- loin pain
- tachycardia
- low BP
Where is the infection in a lower UTI?
Infection of urethra and bladder
Where is the infection in a upper UTI?
infection that reaches kidney
is more severe and can cause sepsis - requires broad spectrum until we know cause
What is the treatment for meningitis?
IV broad spectrum antibiotic: IV ceftriaxone
What bacteria causes meningitis in children/ young adults?
neisseria meningitides
What bacteria causes meningitis in elderly patients?
streptococcus pneumoniae
What would be the diagnosis if a patient with meningitis also had a non-blanching rash and was systemically unwell with low BP and tachycardia?
meningococcal septicaemia - bloodstream infection
What is sepsis?
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
What is the acronym for management of sepsis?
BUFALO: B-blood cultures U-urine output F-fluids A-antibiotics L-lactate O-oxygen
If a patient presents with a tense, red and swollen leg, what would you suspect?
- cellulitis IF there is a history of trauma
- if not, DVT
what is cellulitis caused by?
gram positive cocci - staph aureus and strep pyogenes
What do we treat cellulitis with?
treated with flucloxacillin
What is necrotising fasciitis and how do we treat?
- a severe SSTI caused by a polymicrobial mix, but usually involving streptococcus pyogenes
- treatment: first debridement, then meropenem + clindamycin
What is infective endocarditis?
- infection of heart valves
- most common bacteria are S.aureus and streptococci
Which are the most well tolerated antibiotics in pregnancy?
Beta lactams - penicillins and cephalosporins
Which antibiotics should be avoided in pregnancy?
- quinolones - damage to cartilage
- trimethoprim - folic acid antagonist
- tetracyclins - deposits and stains bones/teeth
What patient factors might influence antibiotic prescriptions?
- allergies
- elderly can’t take some drugs
- some patients can’t take oral or IV antibiotics
- some patients have renal impairment so we have to avoid nephrotoxic drugs
- pathogen might be resistant
- some antibiotics interact with drugs a patient is alreayd on
What are the symptoms and signs of community acquired pneumonia?
- cough
- sputum production
- pleuritic chest pain
- sore throat
- runny nose
- hypoxia
- tachypneoea
- abnormal chest examination
- lower lobe consolidation on X-ray
What is tachypnoea?
abnormally fast breathing
Which tests would you perform on a patient with suspected CAP?
- blood cultures
- sputum culture
- chest X-ray
- lumbar puncture
- CT/ MRI
- HIV blood test
What is diagnostic iteration?
a procedure in which repetition of a sequence of operations (tests) yields results successfully closer to a desired result (a high diagnostic probability)
doing something again and again, usually to improve it
CURB Guidelines: If a patient has.... 1. Low severity CAP 2. Low severity CAP but penicillin allergy 3. Medium severity CAP 4. Medium severity CAP but penicillin allergy 5. High severity CAP 6. High severity CAP
- Amoxicillin
- Doxycycline or clarithromycin
- Amoxicillin + clarithromycin
- doxycycline or levofloxacin
- Co-amoxiclav IV + Clarithromycin
- Levofloxacin
What is ESBL?
- Extended spectrum B-lactamase
- antibiotic resistant enzyme in gram -ve bacteria like E.coli
Give 6 antibiotics used to provide cover for gram +ve pathogens
- teicoplanin
- vancomycin
- flucloxacillin
- linezoid
- macrolides e.g clarithromycin
- penicillin/amoxicillin
Give 3 antibiotics used to provide cover for gram -ve pathogens
- aztreonam
- ciprofloxacin
- gentamicin
Give an example of antibiotic used to treat E.coli cystitis
- nitrofurantoin
- trimethoprim
- cephalexin
What should be considered before a test is performed?
- whether it is indicated or not indicated e.g a urine culture test is not indicated in a patient with suspected cellulitis
- how easy they are to do
- how quick they are to do
- how expensive
- how practical
What are the 4 steps in selecting an antibiotic?
- determine what is the infection diagnosis (or working/differential diagnosis)
- identify which bacteria cause this infection
- identify which antibiotics are effective against these bacteria
- of the antibiotics in 3, which have the right charachteristics e.g can be give orally etc
What does PO stand for?
oral formulation available (drugs can be given orally)
If a patient has an intravascular catheter-associated blood stream infection (CRBSI), what test would you perform to confirm the diagnosis?
paired through-catheter and peripheral blood cultures (blood culture from catheter)
What is the treatmenT for CAP?
Amoxicillin/clavulanate and clarithromycin
If the bacteria causing an infection is coagulase negative staphylococci infection, what antibiotic would you prescribe?
vancomycin- very broad gram +ve antibiotic
