TABLE 4.

Comparison of extracellular and intracellular GFP expression by S. dysenteriae strains

Reporter plasmid and strain	GFP expression in iron-replete culturesa			GFP expression in iron-limited cultures
	Mean fluorescence		Fold repressiond	Mean fluorescence		Fold repression
	Extracellularb	Intracellularc		Extracellular	Intracellular
pSR2 (shuA-gfp)
SDU378	24.5	23.2	1.1	47.2	21.9	2.2e
SDU380	60.1	24.4	2.5	122.4f	21.3	5.7e
SDU402	34.4	22.2	1.5	94.0f	23.6	4.0e
pLR9 (dnaY-gfp)
SDU378	657.0	687.8	1.0	690.7	635.3	1.1
SDU380	599.7	459.3f	1.3	791.5	491.9f	1.6
SDU402	818.3	692.2	1.2	820.2	637.6	1.3

^aPrior to invasion of Henle cells, bacteria were grown to an A₅₉₅ of 0.4. The culture was divided, and EDDA was added to one set of cultures (iron limited) as indicated, and the bacteria were grown for two additional hours. 

^bBacteria were incubated with Henle cells to allow for invasion. After 30 min, the supernatant containing the extracellular bacteria was removed and samples were analyzed by flow cytometry. 

^cFollowing 2 h of intracellular growth, bacteria were harvested from infected Henle cells and samples were analyzed by flow cytometry. 

^dFold repression is the mean fluorescence of extracellular bacteria divided by the mean fluorescence of intracellular bacteria. 

^eIntracellular expression is significantly lower than extracellular expression (P < 0.01). 

^fMean fluorescence is significantly different than that of the wild type (P < 0.025).