TABLE 2.

Effect of treatment of bacteria or expression of virulence properties on invasion of HeLa cells by Y. pestis^a

Conditions	No. of exptb	Fold effectc (mean ± SD)
Pgm+; hemin (50 μM) vs. none; 26°C	6	0.96 ± 0.21
Pgm+; Fe (10 μM) vs none; 26°C	4	1.2 ± 0.34
Pgm+ vs Pgm−; 26°C, Fe starved	2	2.3 ± 1.2
Pgm+ vs Pgm−; 26°C, +10 μM Fe	2	1.8 ± 0.58
Pgm+ vs Pgm−; 26°C, +50 μM hemin	2	4.1 ± 2.6
pCD1+ (Lcr+) vs pCD1−; growth at 26°C	8	0.73 ± 0.46
pCD1+ (Lcr+) vs pCD1−; 26°C growth, then 3 h at 37°C	4	0.73 ± 0.19
pCD1+ (Lcr+); 26°C growth, then 3 h at 37 vs 26°C	2	0.32 ± 0.039
pCD1−; 37 vs 26°C for ca. 7 generations	2	0.057 ± 0.026
PsaA+ vs PsaA−; pH 6, 37°C, 7 generations	2	1.3 ± 0.20d
PsaA+ pCD1−; pH 6 vs pH 7, 37°C, 7 generations	2	3.5 ± 1.0
PsaA+ pCD1−; pH 8 vs pH 7, 37°C, 7 generations	2	2.5 ± 0.53
pPCP1+ vs pPCP1−; 26°C	4	18 ± 8.1

^aMid-exponential-phase bacteria were used for studies of the effect of iron status and of the Pgm⁺ locus on invasion; the other studies used late-exponential-phase yersiniae. 

^bExperiments were done on different days. 

^cFold effect is percent invasion by yersiniae treated or expressing a virulence property divided by percent invasion by yersiniae lacking treatment or the virulence property (e.g., for hemin versus none, percent invasion for yersiniae grown in the presence of hemin divided by percent invasion for iron-starved yersiniae). Fold effects on invasion differing from 1.0 by more than two standard deviations or more than twice the half-range are indicated in boldface. 

^dDone only in the 24-well configuration.