Plaque size on BHK cell monolayers for S. flexneri SF622 expressing ipaD, ipaDΔ41-80, or ipaDΔ81-120

StrainRelative invasion (%)aPlaque size (mm)b
None0.0 ± 0NAc
M90T115 ± 71.28 ± 0.23
BS547 (mxiM)0.0 ± 0NA
ipaD100 ± 101.21 ± 0.51
ipaDΔ41-8068 ± 17d1.18 ± 0.15
ipaDΔ81-12048 ± 13d0.91 ± 0.08d
  • a Invasion 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.

  • b Plaque 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).

  • c NA, not applicable because the complete absence of invasion did not give rise to observable plaques.

  • d P ≤ 0.06 by the paired Student t test.