Publication of two companion papers about Legionella in the top journal Water Research
As a result of a recent FWF project (PI: Alexander Kirschner) entitled "Relevance of viable but non-culturable legionellae", two publications have now been published as companion papers in the renowned top journal Water Research.
In the first paper ("Differential development of Legionella sub-populations during short- and long-term starvation"*), our PhD student Barbara Schrammel was able to show that Legionella develop differentiated, non-cultivable sub-populations with different viability signs under long-term starvation stress. These sub-populations remain stable for several months. The majority of the populations showed low intracellular activity and partially damaged cell membranes, but a small proportion remained with intact cell membranes and high intracellular enzyme activity for up to one year.
In the second part of the study, which was led by our post-doc assistant Sílvia Cervero-Aragó ("Starved viable but non-culturable (VBNC) Legionella strains can infect and replicate in amoebae and human macrophages"**) we were able to show for the first time, that these non-culturable legionella which have long been under starvation stress can infect and proliferate intracellularly in amoebae and human macrophages. However, high cell numbers of non-culturable legionellae were necessary for a successful infection and the infection was significantly slower than with culturable cells.
In summary, these studies show for the first time that of the high numbers of non-culturable legionellae often found in engineered water systems, a large proportion are probably not viable or infectious, but a small, highly active viable subpopulation is present that can potentially cause infection. Whether these slow-running infections of macrophages can actually lead to pneumonia in immunocompromised persons still needs to be clarified.
* Schrammel B, Cervero-Arago S, Dietersdorfer E, Walochnik J, Lück C, Sommer R, Kirschner AKT (2018): Differential development of Legionella sub-populations during short- and long-term starvation. Water Research, in press; doi: 10.1016/j.watres.2018.04.027
** Dietersdorfer E, Kirschner AKT, Schrammel B, Ohradanova-Repic A, Stockinger H, Sommer R, Walochnik J, Cervero-Aragó S (2018): Starved viable but non-culturable (VBNC) Legionella strains can infect and replicate in amoebae and human macrophages. Water Research, in press; doi: 10.1016/j.watres.2018.01.058