Numbers of L. pneumophila cells in mono and dual-species biofilms. Variation of the number of cells of L. pneumophila in mono-species biofilm quantified by the three different methods: curves represent the variation of total cell number (black diamond), L. pneumophila hybridized with the PNA PLPEN620 probe (dark grey square) and cultivable L. pneumophila (light grey triangle); bars represent standard deviation (n = 3) (a). L. pneumophila PNA-positive numbers/total cells numbers ratio (dark grey bars) and cultivable L. pneumophila numbers/L. pneumophila PNA-positive numbers ratio (light grey bars) for the mono-species biofilm and dual-species biofilms of L. pneumophila and V. paradoxus (Dual-species 1), L. pneumophila and M. chelonae (Dual-species 2), L. pneumophila and Acidovorax sp. (Dual-species 3) and L. pneumophila and Sphingomonas sp. (Dual-species 4); the ratio values were calculated using the average of the values obtained for the six time point samples (b).