Ecological behaviour of three serogroups of Legionella pneumophila within a model plumbing system

Three Legionella pneumophila strains isolated from water samples and belonging to serogroups (sgs) 1, 6, and 9 were analysed for their capability to colonise an experimental model simulating a domestic hot water distribution system. Ecological factors that could influence the persistence of sgs as intracellular life within protozoan hosts and bacterial interference by the production of antagonistic compounds were also studied. L. pneumophila viable counts incremented both in the planktonic and in the sessile phases. Serogroup 6 had a marked prevalence during the whole experiment and exhibited the highest host infection efficiency. Serogroup 1 was significantly less represented, but showed the highest capability to reproduce inside the protozoan hosts. Serogroup 9 was poorly isolated and less adapted to the intracellular life. Among 14 bacteria continuously isolated in the system, five (35.7%) produced antagonistic substances against legionella, with differences according to the bacterial strain and L. pneumophila serogroups.