MFD46/48 Practical: Control of infections Flashcards
Describe what amoxicillin is effective against? (spectrum)
2) What can it be combined with to make it more effective?
3) Why does 2 work?
4) what is this combo called?
1) is a moderate-spectrum antibiotic active against a wide range of Gram-positive, and a limited range of Gram-negative organisms.
2) clavulanic acid
3) some resistance to b-lactam-based antibiotics such as amoxicillin is due to the bacteria producing a b-lactamase which hydrolyses the lactam ring. Clavulanic acid binds to and inactivates the enzyme.
4) Amoxicillin and Clavulanic acid
What metronidazole effective against?
Is active against most Gram-positive and Gram-negative anaerobic bacteria
Describe steps of carrying out antibiotic sensitivity test:
- isolate and culture suspected micro. in broth
- spread 100 microlitres of broth over an agar plate, designed for antibiotic suscptibility testing
- suitable range of antibiotics is selected and ring placed agar (mastring) , incubate
- observe
What are breakout colonies in antibiotic susceptibility test?
2) Why do they occur
Sometimes a few of the bacteria in the sample grow and produce colonies within the general area of inhibition.
2) . It occurs when bacteria develop partial resistance to the antibiotic while they are incubated on the agar plate. The lawn of bacteria will soak up the antibiotic to some extent, and the antibiotic concentration reduces as it moves further from the disc. Partial resistance allows the bacteria to grow where the antibiotic is present, but at a relatively low concentration.
What is used to detemine the amount of antiobiotic loaded onto each disc in mastring?
chosen to reflect the amount of that antibiotic which can realistically be expected to achieved at the intended site of action in the body.
What do you measure to assess the sensitvity of the bacteria to the antiobiotic?
2) Why does this work?
1) The size of the ring of inhibition
2) As the antibiotic diffuses out of the Mastring into the growth medium a concentration gradient is set up.
What does MIC stand for?
2) What does MBC stand for?
3) What are they measure of?
4) what essential info do they tell?
5) does it help you work out if there is resistance?
6) is MIC greater or MBC?
Minimum Inhibitory Concentration (MIC) & Minimum Bacteriocidal Concentration (MBC)
3) is a measure of an antibiotic’s efficacy
4) provide essential information regarding delivery of the drug
5) are helpful in determining the appearance of resistance
6) MBC
- In an antibiotic sensitivity test what does the diameter of the zone of inhibition tell us?
It provides an indication of the potency of the antibiotic.
Did the handwashing eliminate, reduce or have no effect on the numbers of bacteria present?
Generally, handwashing does reduce the bacterial load. Sometimes this is not so clear, particularly if hands were fairly clean in the first place.
Hand hygiene is one of the most important methods of ___A___ and there is strong evidence that good hand hygiene can help to limit the spread of infectious diseases in clinical settings.Bacteria presence is ____b___ – it is ___C___ to sterilise skin. You will probably be inoculating your patient with their own bacteria from the ___D________.
A) infection control
B)inevitable
c) impossible
d) epithelial tissue surface
What is the Staph. aureus carriage incidence for the UK population? and MRSA
25-30% of people in the UK carry Staph. aureus in the nose, and about 1-3% harbour MRSA.
The acronym MRSA stands for Methicillin Resistant Staphylococcus aureus. What is methicillin (sometimes called meticillin) and why is resistance to this significant with respect to Staph. aureus?
HINT
start with why are they resistant to penicillin
why methicillin?
how to link the to?
Before MRSA, Staph. aureus had already started to gain resistance to some forms of penicillin (e.g. pen G) due to the spread of a β-lactamase enzyme. However, the main mechanism of methicillin resistance comes from the acquisition of an altered form of a penicillin binding protein, PBP2A, from a foreign source. This protein is a transpeptidase with low affinity for the β-lactam ring of penicllins. Following acquisition of PBP2A, some Staph. aureus strains effectively became resistant to all penicillins.
- Why is the MIC for a particular antibiotic almost always lower than the MBC?
MIC is the concentration required to inhibit growth, whereas MBC is the concentration needed to kill cells. It is easier to stop growth than to actually kill cells, so it always takes at least as much antibiotic to kill cells compared with simply stopping growth
- A microbiologist simply reports that the presumptive microorganism is either sensitive or resistant to the antibiotics used in the test. But how does he decide what concentration of the antibiotic to prescribe for a patient?
The aim of antibiotic prescribing is to reach the MIC of antibiotic at the site of infection. For a localised infection, it may be sufficient to apply the antibiotic topically at the MIC. More often, antibiotics are applied systemically either orally or intravenously. Orally administered antibiotics must be absorbed in the gut before reaching the bloodstream. There they will be diluted and possibly metabolised. Achieving the MIC at the infection site therefore depends on the pharmacokinetic properties of the antibiotic
