2004 - 2007
Understanding how Campylobacter jejuni colonizes poultry
Principal Investigator: Brenda Allan, Vaccine & Infectious Disease Organization
BackgroundCampylobacter jejuni is the leading cause of bacterial gastroenteritis in humans in North America. In poultry, the bacterium resides in the gut without detriment to the bird. Poultry products contaminated with the bacterium are implicated as a source of human infection. The long-term goal of this research program is to decrease or eliminate the level of C. jejuni in poultry by vaccination. The first step towards achieving this goal is to better understand the mechanism by which this bacterium colonizes the avian gut.
Research ProgressIt has been shown that some strains of C. jejuni are more adept at colonizing the avian gut than others. The proposed research aims to identify the factors which contribute to these differences. One approach is to introduce random genetic mutations into lab strains of the bacterium and test for their virulence. Differences in ability to colonize can then be correlated with specific genetic differences. The researchers first proposed the use of Sequence Tagged Mutagenesis (STM) to introduce and assess the mutants. However, during the planning stage, another group of scientists began a very similar project using the same technology. Rather than duplicate this effort, Dr. Allan decided to utilize Recombination-based In-Vivo Expression Technology (RIVET), which, at least in other organisms, can detect genes missed by STM. Unfortunately, Dr. Allan’s group was unable to clear some technical hurdles (mainly associated with plasmid construction) necessary to make use of the RIVET method. As a result, the project took a different tact: to screen cattle, poultry and human samples for C. jejuni and compare isolates for the relative frequencies of various genes thought to be involved in virulence.
Forty-nine samples from cattle and 50 from humans were screened for the presence of 14 putative virulence genes (as indicated in the literature). Results of this screen were compared to results on poultry samples tested under a different project.
OutcomesAll putative virulence genes were detected in 20% of the samples. Approximately 60% of the samples were positive for all the genes, except for virB11. No differences were found between cattle and human samples. Although several genes were found less often in poultry samples, there were no clear differences in gene frequency among cattle, human or poultry samples. These results suggest that cattle may serve as a reservoir for strains of Campylobacter that colonize both poultry and humans.
Future WorkSome C. jejuni isolates have many putative virulence genes, while others have few. These 2 classes of strains will be tested for their ability to colonize chicks. Two animal models will be used:
In the Standard Model, all birds will be orally challenged with the appropriate dose of C. jejuni in a 0.5 mL volume. Colonization of the birds will be monitored by culturing cloacal swabs on Karmali Medium (Bacto) and growing under microaerophilic conditions. Five birds in each group will be tested for colonization by C. jejuni before the group was challenged. Birds will be maintained for seven days after challenge then euthanized by cervical dislocation. Ceca will be aseptically collected for quantitative assessment of colonization on day 7.
The Horizontal Transfer Model will assess the ability of C. jejuni to colonize orally challenged birds and unchallenged birds that are placed in contact with them. Only 20% of the birds will be challenged and marked for identification. All birds will be treated as described above. The use of the two models assesses the full range of colonization potential and will discriminate between different mutants.This work may lead to information useful in determining what factors are involved in gut colonization by C. jejuni.
PublicationsHannon SJ, Taboada EN, Russell ML, Allan B, Waldner C, Wilson HL, Potter A, Babiuk L, Townsend HG. Genomics-based molecular epidemiology of Campylobacter jejuni isolates from feedlot cattle and people in Alberta, Canada. J Clin Microbiol. 2008 Nov 26