Protozoan Acanthamoeba polyphaga as a potential reservoir for Campylobacter jejuni

Abstract

We showed by a laboratory experiment that four different Campylobacter jejuni strains are able to infect the protozoan Acanthamoeba polyphaga. C. jejuni cells survived for longer periods when cocultured with amoebae than when grown in culture alone. The infecting C. jejuni cells aggregated in amoebic vacuoles, in which they were seen to be actively moving. Furthermore, a resuscitation of bacterial cultures that were previously negative in culturability tests was observed after reinoculation into fresh amoeba cultures. After spontaneous rupture of the amoebae, C. jejuni could be detected by microscopy and culturability tests. Our results indicate that amoebae may serve as a nonvertebrate reservoir for C. jejuni in the environment.

FIG. 1.

Experimental setup (see text for details).

FIG. 2.

Early in the infection model, C. jejuni cells aggregated at certain positions on A. polyphaga cell walls (A and B), and after some time, live bacterial cells were observed in amoebic vacuoles (C and D). Subculturing of culture-negative samples together with fresh amoebae at 37°C resulted in lysis of the amoebae, after which live C. jejuni cells could be retrieved (E).

FIG. 3.

In situ hybridization with a fluorescent EUB338 probe identified the presence of intact bacterial cells within amoebic vacuoles.

FIG. 4.

Mean percentages of retained culturability of C. jejuni grown in different media and at different temperatures. CI, confidence interval.