The bacterium called Campylobacter jejuni holds the world record as the bacterium that causes the most gastro-intestinal infections in humans. This bacterium is found in the intestinal tract of healthy poultry where it does not cause problems. Even though the birds are colonized with C. jejuni over their lifetime, it is the contamination of carcasses and water at the slaughterhouse that leads to human infection. For example, water contaminated with poultry feces can contaminate other foods and humans develop illness by eating food (e.g. chicken meat) or ingesting water contaminated with C. jejuni. A significant amount of time and effort are spent reducing the persistence of this pathogen in poultry and trying to eliminate its presence on foods. Another approach that can be used to prevent human infections is to limit the presence of this pathogen in the environment in order to reduce its transmission. To have an effective control strategy, we must first understand how this bacterium survives in environments that are harsher than the digestive tract of poultry. Notably, there are few studies investigating the survival of Campylobater in water.
The protozoa Tetrahymena, (incomplete, in blue) is a unicellular organism living in fresh water. This protozoan is back from hunting bacteria (in green), which forms part of its normal diet. This bacterium is stored with other ingested material in a digestive vacuole. Once digestion is complete, the protozoan compacts residues from its meal into a larger fecal ball as a multilayered sac (in red). However, certain bacteria, such as Campylobacter, survive the digestive process and will get stocked in the multilayered sac. Once the sac is extruded from the protozoan, it protects the bacteria from the hostile environment.
Photo Credit : Alix Denoncourt, Steve Charette and Richard Janvier.
In 2005, researchers demonstrated that drinking water on poultry farms contained Campylobacter as well as protozoans. The majority of these microorganisms live in water while some also live in the intestinal tract of animals. Of the latter, only a few protozoans are dangerous to human or animal health (e.g. malaria, leishmaniasis). Protozoans generally eat bacteria and, interestingly, some bacteria survive within protozoans using them as host organisms.
At McGill University, Sébastien Faucher’s research group is specifically interested in the behaviour of bacteria in water. In his laboratory, postdoctoral fellow Hana Trigui uses the latest technology to monitor how bacteria respond to hostile environments. The McGill group is collaborating with Steve Charette’s group that specialises in the study of protozoans at Université Laval. His research assistant, Valérie Paquet, is an expert in the co-culture of bacteria and protozoa in the laboratory.
With funds from the Swine and Poultry Infectious disease research center (CRIPA) and the MAPAQ (Innov’Action Agroalimentaire Program), this CRIPA member led collaboration demonstrated that Campylobacter survive in the protozoan Tetrahymena pyrformis. In fact, Tetrahymena will ingest these bacteria and following ingestion, these bacteria survive digestion and are excreted by the protozoa in multilayered sacs called multilamellar bodies. Campylobacter uses this protozoan produced sac to survive and remain viable in water for at least 60 hours, which is a half day longer than free-living bacteria that are not protected by a sac.
Is this a strategy to survive to the chlorination or the pH adjustment of water? Do these sacs represent another source of contamination of carcasses at the processing plant? How do we destroy or prevent the formation of these multilayered sacs? These are some of the questions that these groups will try to answer in the future.
Source : Appl. Environ. Microbiol. doi:10.1128/AEM.03921-15. Packaging of Campylobacter jejuni into multilamellar bodies by the ciliate 2 Tetrahymena pyriformis. Auteurs : Hana Trigui, Valérie E. Paquet, Steve J. Charette, and Sébastien P. Faucher