Viability and infectivity of viable but nonculturable Legionella pneumophila strains induced at high temperatures

WATER RESEARCH

卷:158

Article

Cervero-Arago, Silvia^1,2  Schrammel, Barbara¹  Dietersdorfer, Elisabeth³  Sommer, Regina^1,2  Lueck, Christian⁴  Walochnik, Julia³  Kirschner, Alexander^1,2,5 

[1] Med Univ Vienna, Inst Hyg & Appl Immunol, Water Hyg, Kinderspitalgasse 15, A-1090 Vienna, Austria

[2] Interuniv Cooperat Ctr Water & Hlth, Vienna, Austria

[3] Med Univ Vienna, Inst Specif Prophylaxis & Trop Med, Kinderspitalgasse 15, A-1090 Vienna, Austria

[4] Tech Univ Dresden, Inst Med Microbiol & Hyg, Med Fac Carl Gustav Canis, Helmholtzstr 10, D-01069 Dresden, Germany

[5] Karl Landsteiner Univ Hlth Sci, Div Water Qual & Hlth, Dr Karl Dorrekstr 30, A-3400 Krems, Austria

关键词: Legionella;    VBNC;    Acanthamoeba;    Macrophages;    Thermal disinfection;    Viability;   

DOI  :  10.1016/j.watres.2019.04.009

来源: Elsevier

【 摘 要 】

Thermal disinfection is commonly used to prevent the proliferation of culturable Legionella in engineered water systems (EWS). In response to such stress, culturable Legionella populations can switch into a viable but nonculturable (VBNC) state. The importance of such VBNC Legionella cells is currently hotly debated. Here, we investigated the stress response patterns and transitions of the bacteria to the VBNC state at 55 degrees C, 60 degrees C and 70 degrees C on two L. pneumophila strains for >80 days using a combination of cell-based viability indicators. Complete loss of culturability at 55 degrees C, 60 degrees C and 70 degrees C occurred after 3-8 h, 60 min and <2 min, respectively. In contrast, L. pneumophila strains required 9 days at 55 degrees C, 8 h at 60 degrees C and 20 min at 70 degrees C to achieve a 2 log reduction in cells with intact membranes and high esterase activity; a 4 log reduction was achieved only after 150, 8-15 and 1-4 days, respectively. In parallel, the presence of diagnostic outer-membrane epitopes (OMEs) and changes in the infectivity patterns of the two strains towards amoebae and THP-1 cells were assessed. OMEs were more persistent than viability indicators, showing their potential as targets for VBNC Legionella detection. L. pneumophila strains infected amoebae and THP-1 cells for at least 85 days at 55 degrees C and 60 degrees C and for up to 8 days at 70 degrees C. However, they did so with reduced efficiency, requiring prolonged co-incubation times with the hosts and higher Legionella cell numbers in comparison to culturable cells. Consequently, infection of amoebae by thermally induced VBNC L. pneumophila with lowered virulence can be expected in EWS. Although the gold standard method cannot detect VBNC Legionella, it provides important information about the most virulent bacterial subpopulations. Our results indicate that a prolonged thermal regime >= 60 degrees C at the central parts of warm water systems is not only effective against culturable L. pneumophila but in the long run even against VBNC cells. (C) 2019 Elsevier Ltd. All rights reserved.

【 授权许可】

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