Microbiology

Question 1

What is the difference between gram positive and negative micro-organisms?

Answer 1

Gram +ve have thick cell walls exposed to the surface
Gram -ve have thin cell walls protected by a membrane

Question 2

Which are beta lactam antibiotics and how do they work?

Answer 2

Penicillins, carbopenems and cephalosporins

Bactericidal - through cell wall destruction

Mostly broad spectrum - taz, mero, imipenem and ceftazidime cover strep, staph, gram -ve and pseudamonas

Question 3

Which are the glycopeptides, how do they work and which pathogens do they cover?

Answer 3

Vancomycin and teicoplanin

Bactericidal - through cell wall destruction

Active against gram +ve microbes only (strep, staph a. & gram +ve bacilli) - large molecules are unable to cross gram -ve membrane to reach cell wall

Question 4

Which are the aminoglycosides, how do they work and what do they cover?

Answer 4

Gentamycin and amikacin

Bactericidal -inhibit protein synthesis

Main use is for gram -ves (eg ecoli) & pseudamonas

Do have some gram +ve cover but other less toxic antibiotics are more effective

These drugs have a narrow therapeutic index & poor tissue penetration so unlikely to be helpful unless bacteria are present in the bloodstream

Question 5

Which are the macrolides, how do they work and what do they cover?

Answer 5

Clarithromycin, erythromycin and azithromycin

Bacteriostatic - need an active immune system to mop up bacteria otherwise will start multiplying once treatment is stopped

Excellent tissue penetration - covering atypical organisms such as strep, legionella and mycoplasma - NO GRAM -ve COVER

Also cause GI irritation eg diarrhoea

Question 6

Which are the tetracyclines, how do they work and what do they cover?

Answer 6

Doxycycline and tetracycline

Inhibit protein synthesis but not at critical point - bacteriostatic

Good tissue and cell penetration with similar profile to macrolides so can be used interchangeably

Question 7

Which are the quinolones, what do they cover and how do they work?

Answer 7

Levofloxacin & ciprofloxacin

Prevents action of DNA - bacteriocidal

Both have gram -ve & pseudamonas cover
Levo also has some gram +ve cover and is used for resp infections, TB, bone, joint and soft tissue infections

Cipro - UTI & GI and abdo infections
MAJOR ADVERSE EVENTS - ONLY USE IF NO ALTERNATIVE

Question 8

Discuss clindamycin?

Answer 8

Bactericidal
Covers gram +ve cocci & anaerobes
Used for bone, joint, skin and soft tissue infections

Question 9

DIscuss Linezolid

Answer 9

Bacteriostatic
Complicated skin infections, pneumonia & staph a. sepsis

Question 10

Discuss metronidazole

Answer 10

Bactericidal
Anaerobic infections & some protozoa (eg malaria, cryptosporidia)