polyphaga Epigenetics inhibitor which, together with A. castellanii, is one of two FLA frequently used in co-culture experiments. We used trophozoites of the A. polyphaga because this species can be easily infected with L. pneumophila and can be effortlessly grown in vitro[13, 14]. This study aimed to determine the detection limits of co-culture with A. polyphaga compared to conventional culturing methods for L. pneumophila in compost and

air samples. Methods Bacterial and amoebal strains L. pneumophila Philadelphia 1 (Lp1) strain (ATCC 33152) was grown on BCYE (bioMérieux, Geneva, Switzerland) at 36°C for 48 h, re-suspended and adjusted to 1.5 × 108 CFU/ml in 2.5 ml of API® suspension medium (bioMérieux) with an ATB 1550 densitometer (bioMérieux) to prepare the dilutions to be used for spiking. One millilitre of serial dilutions of Lp1 suspension were prepared to obtain a range of 1 × 10 to 1 × 108 bacteria/ml in Page’s saline solution (PAGE: 120 mg/l NaCl, 4 mg/l MgSO4 · 7H2O, 4 mg/l CaCl2 · 2H2O, 142 mg/l Na2HPO4 and 136 mg/l KH2PO4). Acanthamoeba polyphaga (strain ATCC 50362) was grown overnight in peptone-yeast extract-glucose (PYG) medium [17]. The trophozoites were then washed three times and re-suspended in PAGE. Finally, the amoebae were counted and their concentration was adjusted to approximately 9 × 105 cells/ml. Sterile compost and selleck chemicals air samples The compost

was collected in an open-air composting facility in southern Switzerland. Compost samples were sterilized for 15 min at 121°C before spiking to eliminate Legionella cells potentially

present in the compost [4]. Air samples are usually collected in the field with a portable cyclonic air sampler (Coriolis μ, Bertin technologies, Montigny, France) with a flow rate of 250 l/min during 4 minutes and the aspirate is diluted in 10 ml PAGE. Hence, for our experiments we used 10 ml sterilized PAGE samples spiked with known amounts of Legionella cells. Spiking of the compost and air samples the To assess the detection limits and the recovery efficiency of culture and co-culture, 9 aliquots of 5 g sterile compost or of 9 ml of sterile PAGE were spiked with 1 ml of serial dilutions of Lp1 suspension to obtain a dilution range of 1 to 1 × 108 cells per 5 g of compost or per 10 ml PAGE. Ten millilitres of sterile PAGE or 5 g sterile compost re-suspended in 10 ml sterile PAGE were used as negative controls. After spiking, compost and PAGE were thoroughly mixed to distribute bacteria homogeneously in the samples and 9 ml of sterile PAGE were added to the compost. The compost suspensions were mixed during 30 min at room temperature. Recovery of Legionella from spiked samples by conventional culture Ten microlitres of the compost supernatants and of the PAGE samples were diluted 1:100 with 0.2 M HCl-KCl acid buffer (pH 2.2), vortexed three times during 10 min and incubated at room temperature as previously described [18].