TABLE 3.

Plaque size on BHK cell monolayers for S. flexneri SF622 expressing ipaD, ipaD^Δ41-80, or ipaD^Δ81-120

Strain	Relative invasion (%)a	Plaque size (mm)b
None	0.0 ± 0	NAc
M90T	115 ± 7	1.28 ± 0.23
BS547 (mxiM)	0.0 ± 0	NA
ipaD	100 ± 10	1.21 ± 0.51
ipaDΔ41-80	68 ± 17d	1.18 ± 0.15
ipaDΔ81-120	48 ± 13d	0.91 ± 0.08d

^aInvasion is shown relative to that of SF622 expressing wild-type ipaD and with a multiplicity of infection of 1 in six-well tissue culture plates. The data shown are averages of three measurements from a single representative experiment.

^bPlaque size was determined on day 4 following a 3-day incubation of bacteria with BHK cells and including a 1-day incubation in the presence of neutral red (average ± standard deviation obtained with ≥15 randomly selected plaques in each of two independent experiments).

^cNA, not applicable because the complete absence of invasion did not give rise to observable plaques.

^dP ≤ 0.06 by the paired Student t test.