S. flexneri cells used as inoculum were taken from a 30 C
exponential phase culture diluted in phosphate buffered saline
(PBS) to reach 2.6 0.5 107
bacteria per ml. Six microliters of the suspension undiluted, diluted 10-fold and 100-fold (corresponding
to 1.6 0.3 105
,1.6 0.3 104
, and 1.6 0.3 103
bacteria,
respectively) were added to the frozen pellets, in triplicate, and
then transferred back to the freezer until DNA isolation.