Identification of free-living amoebas and amoeba-resistant bacteria accumulated in Dreissena polymorpha

To identify the free-living amoeba (FLA) and amoeba-resistant bacteria (ARB) accumulated in zebra mussels and in the water in which they are found, mussels were collected at two locations in the Ebro river basin (North East Spain). FLAs and bacteria were isolated from mussel extracts and from natural water. PCR techniques were used to identify the FLAs and endosymbiont bacteria (Legionella,Mycobacterium,Pseudomonasand cyanobacteria), and to detectGiardiaandCryptosporidium. The most frequently found FLAs wereNaegleriaspp. The presence ofLegionella,MycobacteriumandPseudomonasinside the FLA was demonstrated, and in some cases bothLegionellaandPseudomonaswere found together. Differences between FLAs and ARB identified inside the mussels and in the water were detected. In addition,Escherichia coli,Clostridium perfringens,Salmonellaspp. andEnterococcusspp. were accumulated in mussels in concentrations unconnected with those found in water. The results show the ability of the zebra mussel to act as a reservoir of potentially pathogenic FLAs, which are associated with potentially pathogenic ARB, although the lack of association between microorganisms inside the mussels and in the water suggests that they are not useful for monitoring microbiological contamination at a specific time.