Microbiology Flashcards
Give some examples of penicillins.
Flucloxacillin
amoxillicin
benzylpenicillin
penicillin V
Describe the mechanism of action of penicillins.
- attaches to penicillin-binding proteins on forming bacterial cell walls
- this inhibits transpeptidase enzyme which cross-links bacterial cell wall
- failure to cross-link induce cell autolysis
When should flucloxacillin be used?
- soft tissue infection
- staphylococcal endocarditis
- otitis externa
Which drug should be used in non-severe CAP?
amoxicillin
List common side effects of penicillins.
- diarrhoea
- vomiting
- liver function impairment
- hypersensitivity reactions (anaphylaxis)
Clavulonic acid is often given alongside which drug? And why?
amoxicillin, as it is beta-lactamase susceptible (mechanism of resistance) - forming co-amoxiclav
Gentamicin is an example of which type of antibiotics?
aminoglycosides
How does gentamicin work?
- binds to 30s ribosomal subunit, inhibiting protein synthesis, inducing a prolonged post-antibiotic bacteriostatic effect
- bactericidal action on cell wall results in rapid killing early in dosing interval and is prominent at high doses
- provides a synergistic effect when used alongside other antibiotics (e.g. flucloxacllin or vancomycin in gram+ve infections)
When should gentamicin be used clinically?
- severe gram -ve infections e.g. biliary tract infection, pyelonephitis, HAP
- some severe gram +ve infections e.g. soft tissue infection, endocarditis
Nephrotoxicity and ototoxicity are caused by high-dose prolonged exposure to which antibiotic?
Gentamicin
Describe the importance of careful dosing in gentamicin prescribing.
- give high initial dose to take advantage of rapid killing
- leave long dosing interval to minimise toxicity
- measure trough level to ensure it is not accumulating
How many days should you limit gentamicin use to?
3 days - minimise risk of SE
Which antibiotics work by interfering with bacterial DNA replication and repair? Give an example of one.
Quinolones
e.g. ciprofloxacin
Describe the spectrum of use and action of ciprofloxacin.
Broad spectrum bactericidal - both gram+ve and gram-ve cover
List the indications of quinolone antibiotic use.
- gram-ve bacterial infection
- respiratory tract infection
- upper urinary tract infection
- peritoneal infection
- gonorrhoea
- prostatitis
Give some side effects of ciprofloxacin.
- GI toxicity
- QT wave prolongation
- C. diff. infection (antibiotic associated diarrhoea)
- tendonitis (rare)
Ceftriaxone and cephalexin are examples of which type of antibiotic?
Cephalosporin
What is the mechanism of action of cephalosporins?
- attaches to penicillin-binding-proteins on forming bacterial cell walls
- this inhibits transpeptidase enzyme which cross-links bacterial cell wall
- failure to cross-link induces bacterial cell autolysis
Are penicillins or cephalosporins more susceptible to beta-lactamases?
penicillins
Describe the coverage of cephalosporins.
both gram+ve and gram-ve
When should cephalosporins be used?
serious infection - septicaemia/pneumonia/meningitis
What are the common side effects of cephalosporins?
- hypersensitivity reactions
- antibiotic-associated C. diff. diarrhoea
- liver function impairment
How is cephalosporins excreted?
kidneys
Cephalosporins have a long half-life, what impact does this have on their use?
needs to be given once daily
Which antibiotic group is bactericial, inhibiting cell-wall synthesis in gram+ve bacteria?
glycopeptides e.g. vancomycin
Which antibiotic is most commonly utilised in MRSA infection?
vancomycin
What are the clinical uses of vancomycin?
- severe gram+ve infections
- MRSA
- severe C. diff. infection
Vancomycin has many side effects. What are they?
- fever
- rash
- local phlebitis at site of injection
- nephrotoxicity
- ototoxicity
- blood disorders - neutropaenia
- anaphylactoid reaction if infusion rate too fast
How is vancomycin administered?
either given as a continuous IV infusion or as a pulsed infusion regimen
Why is therapeutic drug monitoring undertaken with vancomycin?
it has a narrow therapeutic range
Give two examples of macrolides.
clarithromycin
erythromycin
Describe the mechanism of action of macrolides.
- bacteriostatic and bacteriocidal
- binds to 50s ribosomal subunit
- inhibits bacterial protein synthesis
When should macrolides be used?
- atypical organisms causing pneumonia/severe CAP
- severe campylobacter infection
- mild/moderate skin and soft tissue infection
- otitis media
- Lyme disease
- H. pylori eradication therapy
Which antibiotics use the hepatic enzyme cytP450 pathway? And so what drugs do they interact with?
macrolides - and so interact with all drugs using this pathway e.g. simvastatin, atorvastatin, warfarin
What important patient information needs to be given when administering macrolides?
- risk of diarrhoea
- senses of smell and taste may be disturbed
- tooth and tongue discolouration may occur
Describe the mechanism of action of trimethoprim.
- inhibits folate metabolism pathway and leads to impaired nucleotide synthesis
- therefore interferes with bacterial DNA replication
What are the indications of trimethoprim?
- first line antibiotic in uncomplicated UTI
- acute/chronic bronchitis
- pneumocystis pneumonia
- gram -ve, gram +ve and some MRSA cover
List the side effects of trimethoprim.
- elevated serum creatinine
- hyperkalaemia - especially in those with impaired renal function
- depressed haematopoiesis
- rash and GI disturbance
Note some important PK and PD of trimethoprim.
- penetrates well into the prostate - suitable for men with uncomplicated UTI
- avoid in first trimester of pregnancy
- resistant organisms
What are the 4C’s that cause C. diff infection?
clindomycin, co-amoxiclav, cephalosporin, ciprofloxacin
Briefly describe the pathophysiology of C. diff infection.
- infection causes pseudomembranous colitis leading to severe diarrhoea, abdominal pain, fever and nausea
- toxins induce inflammation and cell death
List some anaerobes.
- clostridium
- bacteroids
List some gram+ve coccus bacteria.
- staphylococcus
- streptococcus
- enterococcus
List some gram-ve rod bacteria.
- pseudomonas
- haemophilus
- E. coli
- other coliforms
List the 6 investigations that must be carried out within 1hr of sepsis recognition.
- Perform blood cultures
- Antibiotic administration
- Oxygen to achieve target saturation
- Measure lactate and Hb
- IV fluids
- Monitor urinary output hourly
IV amoxicillin should be administered in?
Group A strep infections
pneumococcus
meningococcus
List some gram+ve rod bacteria.
Clostridia
Bacillus
Listeria
Meningococcus is an example of what type of bacteria?
Gram-ve coccus
What is the SIRS criteria?
- Temperature: <36 °C or >38 °C
- Heart rate: >90/min
- Respiratory rate >20/min or PaCO2 <32 mmHg (4.3 kPa)
- WBC <4x10^9/L or >12x10^9/L
What is the standard short course therapy for tuberculosis?
Isoniazid & rifampicin for full 6 months
Pyrazinamide & ethambutol for first 2 months
Which antibiotics are not safe to use during pregnancy? And why?
Tetracyclines: bone abnormalities
Trimethoprim: neural tube defects
Gentamicin: ototoxicity
Quinolone: bone abnormalities
Horizontal gene transfer has more importance in antimicrobial resistance. What are the three mechanisms of horizontal transfer?
Conjugation
Transduction
Transformation
Describe the four main mechanisms of antibiotic resistance.
- Production of enzyme that inactive or modify antimicrobials eg beta lactamases
- Target modification
- Decreasing cell permeability
- Bacteria export drug from inside cell, drug exchanges for protons
What does MRSA stand for?
Methicillin (flucloxicillin) resistant staphylococcus aureus
Which inherited condition is linked to a defect in the gene coding for NADPH oxidase? What is the consequence of this disease?
Chronic granulomatous disease
Recurrent bacterial and fungal infections - abscesses, lung, lymph nodes, skin
Describe the pathophysiology of neutropenia in cancer patients.
Cytotoxic chemotherapy and therapeutic irradiation
Decreased proliferation of haemopoietic progenitor cells
Neutropenia
What is the clinical definition of neutropenia?
<0.5x10^9/L or <1.0x10^9/L and falling
What antibiotics should be prescribed in the immediate management of neutropenic shock?
Pipercillin & tazobactam
What pathogens commonly cause cellulitis?
Beta haemolytic strep group A
S. Aureus
Which antibiotic should be prescribed initially in cellulitis?
Flucloxicillin
Describe the management plan for necrotising fasciitis.
Urgent surgical debridement
Clindomycin
Immunoglobulin
How would you manage a presentation of COPD exacerbation with green sputum?
Hospitalisation
Administer doxycycline or amoxicillin
<5 days