TABLE 1.

Culture-dependent and real-time PCR-monitored necrotrophic growth of L. pneumophilaa

InoculumL. pneumophila CFU/ml (SD)L. pneumophila mip gene copies/ml (SD)
0 h96 h0 h96 h
L. pneumophila (approx 106 cells)7.8 × 105 (2.5 × 105)2.5 × 105 (1.3 × 105)2.4 × 106 (8.6 × 105)6.2 × 105 (6.3 × 104)
L. pneumophila + 109 live P. putida cellsNA3.7 × 106 (1.9 × 106)
L. pneumophila + 103 dead P. putida cells4.2 × 105 (2.6 × 105)3.5 × 106 (9.6 × 105)
L. pneumophila + 104 dead P. putida cells3.8 × 105 (9.5 × 104)9.8 × 105 (4.5 × 105)
L. pneumophila + 105 dead P. putida cells6.5 × 105 (3.6 × 105)3.5 × 106 (1.8 × 106)
L. pneumophila + 106 dead P. putida cells4.5 × 105 (3.1 × 105)4.6 × 106 (1.7 × 106)*
L. pneumophila + 107 dead P. putida cells6.9 × 105 (2.6 × 105)9.1 × 106 (2.0 × 106)*
L. pneumophila + 108 dead P. putida cells5.3 × 106 (1.1 × 106)*4.8 × 107 (9.6 × 106)*
L. pneumophila + 109 dead P. putida cells1.1 × 107 (7.2 × 106)*8.9 × 107 (2.0 × 107)*
L. pneumophila + 109 dead E. coli cells6.3 × 106 (2.6 × 106)*6.5 × 107 (1.3 × 107)*
L. pneumophila + 109 dead L. plantarum cells6.0 × 105 (4.2 × 105)7.5 × 105 (5.2 × 105)
L. pneumophila + 109 dead B. subtilis cellsNA1.8 × 105 (8.6 × 104)
L. pneumophila + 108 dead A. castellanii cells6.8 × 106 (3.0 × 106)*4.8 × 107 (1.3 × 107)*
L. pneumophila + 109 dead S. boulardii cells5.5 × 106 (2.8 × 106)*1.1 × 107 (8.2 × 106)*
L. pneumophila + heat-treated biofilmNA2.9 × 107 (7.6 × 106)*
  • a Necrotrophic growth of L. pneumophila in sterile tap water on heat-killed (30 min, 60°C) microbial cells was measured. All L. pneumophila starting concentrations were approximately 106 CFU/ml. Quantification of L. pneumophila cells during 96 h was performed using plate counts on BCYE agar and real-time PCR targeting of the mip gene. Numbers presented are mean values of five repetitive experiments for which each separate experiment was measured in triplicate. An asterisk indicates significant necrotrophic growth of L. pneumophila compared to the starting concentration. NA, not available due to bacterial overgrowth.