CLED agar help please

[elainegardener]

I am a student at the University of Portsmouth studying part time for BSc in Applied Science. One of the units taken is clinical microbiology and I have a query relating to CLED agar.

I performed a disk diffusion test on a CLED agar plate inoculated with E.coli. A disk of Trimethoprim was added and incubated to observe growth. The antibiotic disk had some effect upton the growth but had not completely inhibited it - there was no clear zone of inhibition. I have attached a photo of the plate.

http://photos-e.ak.fbcdn.net/hphotos-ak-snc3/hs058.snc3/14564_225395194746_511344746_4206508_7099041_n.jpg

I was wondering if there was a certain substance in the CLED agar that contributed to this?

Regards

Elaine Gardener MSB

[biohazard]

Are you sure you do not have two kinds of microbes growing on the plate now. I cannot quite tell for sure from that photo of yours, but it might be that there is another, resistant microbe growing in addition to E. coli on the plate. There seem to be these larger, whitish colonies that are inhibited (E. coli) and then smaller, deep yellowish ones that are resistant (perhaps some cocci).

You could try to spread some of the bacteria on the plate onto a new one and disperse the bacteria so that you get isolated colonies in order to see if you have two different types of colonies.

CLED should not have any special features regarding E. coli growth, it just prevents the plate being overgrown by e.g. Proteus species. Also, Trimethoprim should not cause this kind of phenomenom if used with pure culture of E. coli .

[elainegardener]

Yes I agree, this is why I was slightly confused with the phenomenon.

We had to spread the E.coli onto DSTA and CLED and observe the results. We then had to discuss the mechanisms involved in the results observed in relation to the effect of culture media and Trimethoprim.

Unfortunately I am unable to do any further investigations on the CLED orgnisms.