Of chickens, wild birds and men – host specificity in Campylobacter jejuni

Rule number one in the kitchen: be wary of chickens! Improperly handled, this meat may spice up your dish with unwanted avian gut bacteria. The most notorious chicken bug is Campylobacter jejuni – which gives you really, really bad gastroenteritis (or ‘shits’ as most of you would say).

Campylobacter

C. jejuni is a quite common bug. At the poultry flock level, prevalence vary between 0 and 90% depending on which time of the year it is (more in summer months), which country we are talking about (less at northern latitudes), and of course the hygiene level of the farm in question (greasy farms get more bugs). However, nice Campylobacter-free chickens may be soiled with bacterial cells from infected birds during the long winding road from the farm, through the various stations in the abattoir (de-feathering stations, rinsing etc.) and to the retail level and end-consumer.

In our research we have addressed wild birds as hosts for campylobacters. Over the years we have spent a lot of effort to find out which bird species that are carriers of campylobacters, and which that are not. And what kind of differences there are between bacteria from different bird species. Earlier this year, we published a study in Molecular Ecology, where we genotyped a large collection of C. jejuni collected from Sweden, England and Australia. For a full view, down-load it here: http://onlinelibrary.wiley.com/doi/10.1111/mec.12144/full

We used multilocus sequence typing (MLST), which is equal to sequencing parts of seven different housekeeping genes distributed around the bacterial chromosome. Each unique allele gets a number, and the combined row of numbers of the seven loci is used to create a sequence type (ST). A sort of fingerprinting, you could say. And a very handy technique for C. jejuni, as it is one of the most recombinatory bacteria we know of; tree-based methods for inferring relationships don’t work as good on campylobacters.

mec12144-fig-0001

We found two things: First, C. jejuni populations in wild birds have very different genetic structure from C. jejuni in farm animals. In the figure above, you see how all human and food-animal C. jejuni populations cluster together, and where the different wild bird hosts have distinct populations of bacteria with long branch lengths. Second, we found strong patterns of host specificity.

Have a look at the picture again. If you look carefully, you will see that dunlins in Sweden and sharp-tailed sandpipers in Australia have more or less similar C. jejuni, despite huge geographic distances! Same goes for black-headed gulls and silver gulls, very similar to one another, but very different from the waders! And have a look at the blackbird – introduced to Australia by acclimatization societies in the 19th century they seem to have retained similar genotypes of C. jejuni that modern blackbirds have in Europe! Remarkable!

This really tells you of host adaptations – there are certainly differences in the enteric environment of different bird species, and in their diets, but there may also be differences in ecology that affects transmission properties, or survival in the environment. And why is all this important? Well, it says something about the peculiarity of current food animal C. jejuni. In these hosts, C. jejuni are more genetically similar and have a larger host range, suggesting that particular features involved in survival and transmission in the farm environment has caused expansion of particular genotypes.

In the future, identifying these properties are key. Hopefully we could do that with our wild bird campylobacters. But in the mean time, wash your hands and cook your chicken properly.

Jonas Waldenström

http://onlinelibrary.wiley.com/doi/10.1111/mec.12144/full

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One thought on “Of chickens, wild birds and men – host specificity in Campylobacter jejuni

  1. Pingback: Two new doctors – and some notes on the procedures at a Swedish PhD defense | Zoonotic Ecology and Epidemiology

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