Week 6 Flashcards
(182 cards)
Describe the difference between gram positive and negative bacteria
positive have a thick peptidoglycan wall
negative have thin peptidoglycan wall and periplasm and outer membrane
Where can antibiotics target?
cell wall peptidoglycan
metabolism
DNA
ribosome
Describe the action of bactericidal antibiotics
achieve sterilisation of the infected site by directly killing bacteria
lysis of bacteria can lead to release of toxins and inflammatory material
Describe the action of bacteriostatic antibiotics
suppresses growth but do not directly sterilise infected site
requires additional factors to clear bacteria - immune mediated killing
What is meant by the antibiotic spectrum?
refers to the range of bacterial species effectively treated by the antibiotics
Describe the spectrum of meropenum
active against almost all gram positive and negative species. Resistance is rare except for MRSA
Describe the spectrum of benzyl-penicilin
highly active against streptococci. most other disease causing bacteria are resistant
Describe broad spectrum antibiotics
active against a wide range of bacteria
treat most causes of infection but also have a substantial effect on colonising bacteria
Describe narrow spectrum antibiotics
active against limited range of bacteria
useful where cause of infection is well defined
much more limited effect on colonising bacteria
What are the main gram positive bacteria?
clostridum
streptococcus
enterococcus
staphylococcus
What are the main gram negative bacteria?
bacteroides psuedomonas haemophilus neisseria e.coli other coliform
What is guided therapy?
depends on identifying cause of infection and selecting agent based on sensitivity testing
What is empirical therapy?
best guess therapy based on clinical/epidemiological acumen
used when therapy can’t wait for culture
What is prophylactic therapy?
preventing infection before it begins
What can the disruption of bacterial flora lead to?
overgrowth with yeasts - thrush
overgrowth of bowel - diarrhoea
development of C.dif colitis
future colonisation and infection with resistant organisms
What are the main classes of beta-lactam antibiotics?
penicillins
cephalosporins
carbapenems
monobactams
Describe the overall mechanism of action of b lactams
all share same structural feature
Beta-lactam motif analogue of branching structure of peptidoglycan
inhibits cross linking of cell wall peptidoglycan
causes lysis of bacteria - bacteriocidal
What are beta-lactamases?
enzymes that lyse and inactivate beta-lacta drugs
commonly secreted by gram negatives and S.aureas
confer high level resistance to antibiotic - high doses will not overcome it
Describe the pharmacology of beta-lactams
poorly absorbed in GI tract
usually excreted unchanged in urine, some also via bile
half life varies enormously
effectively distributed to infection sites
Which beta-lactams can be effective orally?
amoxicillin, flucloxacillin
vomiting limits dose
Describe the cross reactivity of penicillin allergy
patients allergic to a penicillin will usually be allergic to others
cross reactivity with other antibiotic classes is much lower
What are common penicillin?
benzyl-penicillin
amoxicillin
flucloxacillin
What is a common cephalosporins?
ceftriaxone
What is a common carbapenem?
meropenem