4Bureau of Microbial Hazards, Health Canada, Frederick G. Banting Building, Ottawa, Ontario, K1A 0L2, Canada

Campylobacter jejuni is a significant food- and waterborne pathogen both in North America and abroad and a considerable cause of child morbidity in underdeveloped countries. The primary source of campylobacter infection in humans is through the consumption of contaminated poultry products although two recent waterborne outbreaks in Canada and the USA demonstrate that water is also an important source for infection

We observed differences in virulence of two C. jejuni NCTC11168 variants, CJ1 and CJ26 when they were tested in the young chick model. CJ1 was much more efficient in colonizing chicks than CJ26. CJ26 had been maintained in the laboratory for many years while CJ1 was obtained from the American Type Culture Collection. We were interested in determining what changes has occurred in the lab adapted strain CJ26 that lead to a decrease in the ability to colonize birds.

To determine what changes had occurred we used a genomic approach. This was facilitated by the fact that the genome of C. jejuni NCTC11168 had been sequenced. As well researchers at the Institute of Biological Sciences have developed a Campylobacter microarray.

A microarray is a glass slide with the many genes spotted on it in an ordered pattern. In this case the microarray contained over 90% of the potential genes in the chromosome of C. jejuni.

To compare the gene expression of CJ1 and CJ26 messenger RNA was isolated from each type of bacteria. The messenger RNA was converted into cDNA. The cDNA from each type of bacteria was labeled with a fluorescent tag. Different tags (red and green) were used so that the samples can be differentiated in subsequent steps. The two labeled samples are mixed and incubated with the microarray. The labeled DNA molecules bind to the DNA on the array corresponding to the genes expressed in each type of bacteria.

After the hybridization (binding) step was complete the microarray was placed in a scanner that consists of at least two lasers, a microscope and a camera. The fluorescent tags were excited by the laser and the microscope and camera produce a digital image of the array. These data were stored in a computer and a special program was used to calculate the intensity of the red to green fluorescence of every spot on the array.

The colour of the spot reflects the level of expression. If both types of bacteria express the gene at the same level the spot will be yellow. If the bacteria with cDNA labeled in green expresses more of the gene than the bacteria with the cDNA labeled in red then the spot will be green. The converse is true. If neither bacterium expresses the gene then the spot will not fluoresce.

When we examined gene expression of CJ1 and CJ26 using this technique we observed that CJ1 expressed many genes responsible for flagella production at higher levels than CJ26. We confirmed using electron microscopy that CJ1 produced more flagella than CJ26. We also observed that many other genes were expressed at a higher level in CJ1 than in CJ26. Some genes were also observed to be expressed at a higher level in CJ26. Genes that are over expressed by CJ1 play a potential role in the colonization of poultry.

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