TABLE 2.

Phenotypes of intracellular growth mutants of L. pneumophila

Strain	Pool no.	Fold growth in U937 cellsa	Total errorb	Colocalization with LAMP-1c	Growth on:
					CAA agar	0.65% NaCld
Lp01		1.7 × 103	4.9 × 102	−	+	−
HL900	24	0.56	0.59	+	+	+
HL1000	24	0.68	0.68	+	+	+
HL1300	34	0.66	0.13	+	+	+
HL1400	35	0.72	0.19	+	+	+
HL1600	40	0.34	0.16	+	+	+
HL1700	1	1.1	0.29	+	+	+

^aPhorbol ester-treated U937 cell monolayers were incubated with 10⁵ CFU of L. pneumophila derivatives. Viable counts were determined after 2 h (t₀) and again at 72 h as described (Materials and Methods). Total growth was calculated as total mean CFU at 72 h/total mean CFU at t₀. Values shown are calculated from averages of triplicate samples from a typical experiment. A value of 1 represents equivalent numbers of bacteria at t₀ and 72 h. 

^bTotal growth [(standard error for t₀) + (standard error for 72 h)]. 

^cMeasured as described (Materials and Methods). 

^d+, approximately 100- to 1,000-fold increase in plating efficiency compared to Lp01.