Improved recovery of Legionella from water samples by use of black membrane filters.

A higher recovery of Legionella bacteria from water samples was achieved using black filters that were directly placed on agar plates after filtration, compared to the traditional method using white filters that are shaken in buffer after filtration. Up to 100 times more Legionella colonies/100 ml were found using black filters compared to the traditional method. The two filtration methods revealed, however, no big differences with pure culture experiments. Treatment with acid solution, directly on the filters without dilution of the concentrated sample, effectively reduced the number of accompanying bacteria.