Data were analyzed by anova and a Scheffe’s test. Acinetobacter baumanii can be isolated from many surfaces in hospitals (Beggs et al., 2006; Peleg et al., 2008) and recovered from hospital water (Simor et al., 2002; Huang et al., 2008). Moreover, free-living Selleckchem Selumetinib amoebae are also frequently isolated from the same aquatic environment. It has been previously shown that free-living amoebae can interact with a great variety of microorganisms (Greub & Raoult, 2004). In this work, we investigated the relationships

between A. baumanii and two Acanthamoeba species. In the co-cultures in PAS medium, the presence of A. castellanii or A. culbertsoni induced a major increase in A. baumanii growth, as compared with bacterial growth without amoebae (Fig. 1). The results of these co-cultures were similar in filtered tap water (data not shown). In addition, the viability of A. castellanii was not affected by

the conditions of co-culture selleckchem with A. baumanii as shown by trypan blue exclusion experiments (Table 1). As for Shigella sp. (Saeed et al., 2009), the relationships between these microorganisms may consequently be considered symbiotic. Acanthamoeba culbertsoni/A. baumanii co-culture induced a decrease in the viability of the amoeba, whatever the incubation medium used (PAS or filtered water); nevertheless, when incubated alone in the experimentation medium, the mortality of this amoeba was already high after 72 h (Table 1). This is not the first time that a differential effect of a bacterium has been observed on various amoebae. Dey et al. (2009) recently showed that amoebae are not all equally permissive with regard to L. pneumophila and that some amoebae strains can be particularly resistant to this bacterium. The results of electron microscopy have indicated the location of the bacterium. After 2 h of co-culture, bacteria were recovered only Nitroxoline in the medium with intact trophozoites. After 1 and 3 days,

bacteria were found in vacuoles in the cytoplasm of amoebae trophozoites. At that time, a few cysts were observed, without any bacteria (Fig. 2). It has previously been mentioned that A. castellanii enhances growth of some microorganisms (Greub & Raoult, 2004) and Abd et al. (2005) have shown that Vibrio cholerae O139 may be located in the cytoplasm of A. castellanii trophozoites as well as in the cysts of this amoeba. Moreover, it has recently been proven that some eucaryotes including Acanthamoeba species may prolong the survival of Campylobacter for at least 4 weeks (Axelsson et al., 2010). In addition, it had previously been shown by molecular techniques that A. baumanii could survive and be isolated in co-cultivation with Acanthamoeba polyphaga (Pagnier et al., 2008) or A. castellanii (Thomas et al., 2008), but no microscopic observation has shown the interactions between the microorganisms.