none5noIn man-made water distribution systems, Legionella community interactions remain unknown, due to their ability to change
from sessile to planktonic states or live in viable but non-culturable forms, in response to anthropic and environmental stress.
During 7 years of hospital Legionella surveillance, in 191 hot water positive samples, the interactions among the Legionella
species, temperature, and disinfection treatment were evaluated. Legionella was isolated following ISO 11731:2017, and
identification was performed by mip gene sequencing and sequence-based typing (SBT) for L. anisa or L. rubrilucens
and L. pneumophila, respectively. The species with the higher frequency of isolation was L. pneumophila serogroup 1
(78.53%; 4865.36 ± 25,479.11 cfu/L), followed by L. anisa (54.45%; 558.79 ± 2637.41 cfu/L) and L. rubrilucens (21.99%;
307.73 ± 1574.95 cfu/L), which were sometimes present together. Spearman’s rho correlation test was conducted among the
species with respect to temperature and disinfectant (H2O2/Ag+). The results showed a generally positive interaction among
these species sharing the same environment, except for competition between L. anisa and L. rubrilucens. High temperature
(48.83 ± 2.59 °C) and disinfection treatment (11.58 ± 4.99 mg/L) affected the presence of these species. An exception was
observed with L. anisa, which showed disinfection treatment resistance. For the purposes of environmental surveillance, it
is fundamental to better understand the interactions and dynamic of the Legionella community in man-made water systems
in order to choose the proper physical or chemical treatments. The simultaneous presence of different Legionella species
could result in an increased resistance to high temperature and disinfectant treatment, leading to changes in contamination
level and species diversity.openLuna Girolamini, Silvano Salaris, Maria Rosaria Pascale, Marta Mazzotta, Sandra CristinoLuna Girolamini, Silvano Salaris, Maria Rosaria Pascale, Marta Mazzotta, Sandra Cristin