Increase in Acid Tolerance of Campylobacter jejuni through Coincubation with Amoebae

Campylobacter jejuni is a recognized and common gastrointestinal pathogen in most parts of the world. Human infections are often food borne, and the bacterium is frequent among poultry and other food animals. However, much less is known about the epidemiology ofC. jejuni in the environment and what mechanisms the bacterium depends on to tolerate low pH. The sensitive nature ofC. jejuni stands in contrast to the fact that it is difficult to eradicate from poultry production, and even more contradictory is the fact that the bacterium is able to survive the acidic passage through the human stomach. Here we expand the knowledge onC. jejuni acid tolerance by looking at protozoa as a potential epidemiological pathway of infection. Our results showed that whenC. jejuni cells were coincubated withAcanthamoeba polyphaga in acidified phosphate-buffered saline (PBS) or tap water, the bacteria could tolerate pHs far below those in their normal range, even surviving at pH 4 for 20 h and at pH 2 for 5 h. Interestingly, moderately acidic conditions (pH 4 and 5) were shown to triggerC. jejuni motility as well as to increase adhesion/internalization of bacteria intoA. polyphaga . Taken together, the results suggest that protozoa may act as protective hosts against harsh conditions and might be a potential risk factor forC. jejuni infections. These findings may be important for our understanding ofC. jejuni passage through the gastrointestinal tract and for hygiene practices used in poultry settings.