Micro help (again) please?

angeldelight

We were doing tests on antimicrobial susceptibility to antibiotics in the lab and I just ended up really confused. We were trying to identify the MIC for a given antibiotic (ampicillin), so we did serial diffusions with different concentrations of the antibiotic + standard innoculated broth. We had 10 tubes, tube 1 had 1ml of antibiotic (10microg/ml) soln. + 1ml of innoculated broth. Tube 2 had slightly less conc antibiotic + broth etc up to tube 9. Ten just had 1ml of antibiotic @ 10 microg/ml. Tubes 1 and 10 were clear, the others were turbid and that's what I dont get....what do these results mean? Are they susceptible/resistant? Thank you and sorry if this was confusing

Capt'n Midnight

The cloudy tubes have surviving microbes.
Tube 10 had no microbes added so it should be clear (a control)
Tube 1 had the most concentrated antibiotic and since it was clear then the concentration is high enough to stop the little beggers breading.

If only one organism survived in tube 2 (probably resistant) and the incubation time was long enough and the doubling time was short enough it could still be cloudy as now there are more of them. Tube 9 should have a lot more organisms surviving so less natural selection there.

John

Capt'n Midnight wrote:

The cloudy tubes have surviving microbes.
Tube 10 had no microbes added so it should be clear (a control)
Tube 1 had the most concentrated antibiotic and since it was clear then the concentration is high enough to stop the little beggers breading.

If only one organism survived in tube 2 (probably resistant) and the incubation time was long enough and the doubling time was short enough it could still be cloudy as now there are more of them. Tube 9 should have a lot more organisms surviving so less natural selection there.

What he said. Basically it means that from your sample, tube 1 was the only concentration of antibiotic prepared that was strong enough to kill the bacteria. Antibiotics aren't all or nothing, just because a bacterium is resistant to it at one concentration it doesn't mean that it will survive a higher concentration.

What college are you in angeldelight?

angeldelight

Thank you both! I'm in RCSI

John

pity, if you were in TCD I think I have all my corrected micro labs from last year tucked away somewhere.

angeldelight

That IS a pity!! Nice of you to thik of it though, thanks I finish micro at easter anyways. I actually really enjoy it, am gonna look into careers as a hosp pharmacist who specialises in micro

GuanYin

angeldelight wrote:

That IS a pity!! Nice of you to thik of it though, thanks I finish micro at easter anyways. I actually really enjoy it, am gonna look into careers as a hosp pharmacist who specialises in micro

LOL! Erm you're either looking to work abroad or have a rather unrealistic perception of hospital pharmacy job ops.

angeldelight

Well I'm thinking about the UK although I've been speaking to one of the heads of clinical microbiology in one of the hospitals in Dublin and it's something they'll be bringing on board soon

GuanYin

angeldelight wrote:

Well I'm thinking about the UK although I've been speaking to one of the heads of clinical microbiology in one of the hospitals in Dublin and it's something they'll be bringing on board soon

With which money is this now?

Don't hold your breath, there is gonna be a major review of the hospital administration in light of the beaumont scandal and the bed shortage. I'd focus on positions that actually exist.

angeldelight

Afaik they already have funding, some of which is from private sector, cause of resistance strains. I'm mainly focusing on community actually,its that I want to do my masters in. just want to do a few years in hospital at some stage and if I do I'd prefer to do it as someone who does ward rounds with clinical microbiologists. Happens occasionally already, wouldn't be a full-time thing just an extra duty