Detection limits of Legionella pneumophila in environmental samples after co-culture with Acanthamoeba polyphaga

Background: The efficiency of recovery and the detection limit of Legionella after co-culture with Acanthamoeba polyphaga are not known and so far no investigations have been carried out to determine the efficiency of the recovery of Legionella spp. by co-culture and compare it with that of conventional culturing methods. This study aimed to assess the detection limits of co-culture compared to culture for Legionella pneumophila in compost and air samples. Compost and air samples were spiked with known concentrations of L. pneumophila. Direct culturing and co-culture with amoebae were used in parallel to isolate L. pneumophila and recovery standard curves for both methods were produced for each sample. Results: The co-culture proved to be more sensitive than the reference method, detecting 10(2)-10(3) L. pneumophila cells in 1 g of spiked compost or 1 m(3) of spiked air, as compared to 10(5)-10(6) cells in 1 g of spiked compost and 1 m(3) of spiked air. Conclusions: Co-culture with amoebae is a useful, sensitive and reliable technique to enrich L. pneumophila in environmental samples that contain only low amounts of bacterial cells.