When bacteria and free-living amoebae (FLAs) live both in natural waters and man-made aquatic systems, they constantly interact with each other. Some bacteria can survive and grow within FLAs. Therefore, it has recently been thought that FLAs play an important role in spreading pathogenic bacteria in aquatic systems. In this study we investigated the intracellular growing ability of 7 different Gram-negative bacteria (Pseudomonas fluorescens, Pseudomonas putida, Pasteurella pneumotropica, Aeromonas salmonicida, Legionella pneumophila serogroup I, L pneumophila serogroup 3, L. pneumophila serogroup 6) in four different FLA isolates (A1-A4). Among these, four bacterial isolates (P. fluorescens, P. putida, P. pneumotropica, A. salmonicida) and two free-living amoebae isolates (A3, A4) were isolated from the tap water in our city (Istanbul). It was found that 4 different Gram-negative bacteria could grow in A1, 2 different Gram-negative bacteria could grow in A2, 4 different Gram-negative bacteria could grow in A3, 1 Gram-negative bacterium could grow in A4. In conclusion, we think that this ability of growth could vary according to the characteristics of both bacteria and FLA isolates. Also, other factors such as environmental temperature, bacterial concentration, and extended incubation period may play a role in these interactions. This situation can be clarified with future studies. (C) 2014 Elsevier Inc. All rights reserved.