Viable but Not Culturable Forms of Legionella pneumophila Generated After Heat Shock Treatment Are Infectious for Macrophage-Like and Alveolar Epithelial Cells After Resuscitation on Acanthamoeba polyphaga.

[legionellosis]

Legionella pneumophila , the causative agent of legionellosis is transmitted to human through aerosols from environmental sources and invades lung 's macrophages . It also can invade and replicate within various protozoan species in environmental reservoirs . Following exposures to various stresses , L . pneumophila enters a non-replicative viable but non-culturable (VBNC ) state . Here , we evaluated whether VBNC forms of three L . pneumophila serogroup 1 strains (Philadelphia GFP 008 , clinical 044 and environmental RNN ) infect differentiated macrophage-like cell lines (U 937 and HL-60 ), A 549 alveolar cells and Acanthamoeba polyphaga . VBNC forms obtained following shocks at temperatures ranging from 50 to 70 Â Â°C for 5 to 60 Â min were quantified using a flow cytometric assay (FCA ). Their loss of culturability was checked on BCYE agar medium . VBNC forms were systematically detected upon a 70 Â Â°C heat shock for 30 Â min . When testing their potential to resuscitate upon amoebal infection , VBNC forms obtained after 30 Â min at 70 Â Â°C were re -cultivated except for the clinical strain . No resuscitation or cell lysis was evidenced when using U 937 , HL-60 , or A 549 cells despite the use of various contact times and culture media . None of the strains tested could infect A . polyphaga , macrophage-like or alveolar epithelial cells after a 60 -min treatment at 70 Â Â°C . However , heat-treated VBNC forms were able to infect macrophage-like or alveolar epithelial cells following their resuscitation on A . polyphaga . These results suggest that heat-generated VBNC forms of L . pneumophila (i ) are not infectious for macrophage-like or alveolar epithelial cells in vitro although resuscitation is still possible using amoeba , and (ii ) may become infectious for human cell lines following a previous interaction with A . polyphaga .

Diseases
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Diseases presenting "alveolar epithelial cells" symptom

congenital diaphragmatic hernia

legionellosis

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