Description:
<jats:title>Summary</jats:title><jats:p>Quantitative data on <jats:italic>Salmonella</jats:italic> gene expression in infected hosts are largely
lacking because of technical problems. One attractive reporter, the green fluorescent
protein (GFP), is widely used <jats:italic>in vitro</jats:italic> but is difficult to quantify in infected
tissues because of the preponderance of background particles with similar fluorescence.
Here, bacterial GFP emission was spectrally distinguished from host autofluorescence
by two‐colour flow cytometry. Using this technique, the <jats:italic>in vivo</jats:italic> activity of
three well‐characterized promoters (P<jats:italic><jats:sub>sicA</jats:sub></jats:italic>, P<jats:italic><jats:sub>ssaH</jats:sub></jats:italic>
and P<jats:italic><jats:sub>pagC</jats:sub></jats:italic>) was determined. Their spatial and temporal activity
patterns are in close agreement with predictions based on previous data and the colonization
defects of corresponding deletion strains. To identify additional <jats:italic>Salmonella</jats:italic>
promoters that are induced in infected animals, a genomic library was sorted by flow
cytometry yielding four independent promoters. Genes expressed from P<jats:italic><jats:sub>pibB</jats:sub></jats:italic>
and P<jats:italic><jats:sub>sifA</jats:sub></jats:italic> contribute to virulence, and chorismate mutase expressed
from P<jats:italic><jats:sub>aroQ</jats:sub></jats:italic> might participate in aromatic acid biosynthesis, which
is also required for virulence. Promoter P<jats:italic><jats:sub>3g</jats:sub></jats:italic> appears to be part of a mobile genetic element that is lacking in the completely sequenced strain LT2.</jats:p>