Download 14–16 Video transcript: Chickens and Campylobacter

14–16 Video transcript: Chickens and Campylobacter – the lab story
It’s the small things:
Chickens and Campylobacter:
the lab story
So what happens next when the material's back at the lab is that we isolate and grow the Campylobacter. Then we
boil the bacterial cells to extract the DNA, and then we sequence the DNA and this means that we compare the
isolates we've collected this morning with a whole database full of isolates that we have already sequenced. So this
is a way that we can start to investigate how the Campylobacter transfers between different host sources.
We use a black agar plate for Campylobacter, which is specific for this bacteria. It cuts out a lot of the competition
that you would find in faecal samples. You dip a swab into the faecal sample and mix it round a bit, and then you
spread using a loop on the plate.
It's incubated for 48 hours in a special atmosphere, and then we do follow-on characterisation tests to confirm the
identity of the bacteria. Then we would sub-culture it onto a blood agar, which is the red agar plate, to get a pure
culture, to then go on and extract the DNA.
Once we've got the pure culture of the bacteria, we make a dense suspension in phosphate-buffered saline, and
then we boil it in a water bath for 10 minutes. Then this means that the bacterial cells burst open and release the
DNA.
So then we start off doing a PCR reaction, where we use primers to target the part of the gene that we're interested
in. Actually, for this technique we're using parts of seven genes, and the combination of that, once we've got the
DNA sequenced, is, in effect, like a shop barcode. And it's a way of easily distinguishing between different strains
of the Campylobacter.
Here we're setting up the sequencing reactions by transferring the reagents into a 96-hole plate, which will be run
on the DNA sequencer. So when I've set up the sequencing reactions and they've all been cleaned up, then we
take them to our sequencing lab upstairs, and they're run through an automated DNA analyser.
We get the data back as electropherograms. We then assemble a forward and reverse strand, so that's to doublecheck that the sequence is correct. That then translates into a text file, and the text file is then very easily portable
and checkable against all of the other Campylobacter strains that we already have on the database.
It makes it a very good technique to compare with the research groups around the world. The results from this
study show that chickens and wild birds actually carry, they look to carry for a majority of cases very different
Campylobacter strains. So wild birds aren't implicated in colonising chickens.
So then we need to look for a different source of where chickens are getting chicken-type Campylobacters from.
And the most likely thing is they pick it up from other chickens.
The industry is really complicated and complex, and so it opens up a whole new line of enquiry really.
We know that Campylobacter affects humans. If they come across Campylobacter, they will be ill. Chickens, they
can be colonised with Campylobacter and we don't necessarily see that they have a problem. Recent evidence
suggests that Campylobacter may be causing a bit more of an issue in some circumstances in some birds than
was previously thought.
By understanding more about the bacteria and how it transfers between chickens and humans, we hope to, in the
future, find ways of reducing levels in chickens and then ultimately in human disease.
1