<i>S. paratyphi</i> B requires PmrD to express PmrA-dependent genes and to resist polymyxin B during growth in Fe³⁺.

<p>(A) β-galactosidase activity (Miller units) produced from a <i>pbgP-lac</i> transcriptional fusion in the following strains: <i>S. typhimurium</i> (EG9241), <i>S. paratyphi</i> B (EG16652), <i>S. paratyphi</i> B <i>(pmrA G211</i>) (EG16275), <i>S. paratyphi</i> B Δ<i>pmrD</i> (EG16277), <i>S. paratyphi</i> B <i>pmrA</i> (<i>G211</i>) Δ<i>pmrD</i> (EG16276), and <i>S. paratyphi</i> B Δ<i>pmrA</i> (DC167). Bacteria were grown in N-minimal medium at pH 7.7 with low Mg²⁺, high Mg²⁺ or low Mg²⁺ and high Fe³⁺. Data correspond to the mean values of three independent experiments performed in duplicate, and error bars show standard deviation. Asterisks indicate statistically significant differences based on a two-tailed Student t-test (p<0.05). (B) β-galactosidase activity (Miller units) produced from a <i>pbgP-lac</i> transcriptional fusion in isogenic <i>pmrD⁺</i> or <i>pmrD⁻ S. typhimurium</i> strains harboring either the <i>pmrA</i> (<i>E211</i>) or (<i>G211</i>) allele (EG9241, EG11775, EG14331 and DC300) were determined as described in (A). (C–D) Growth of <i>S. enterica</i> strains harboring either the <i>pmrA</i> (<i>E211</i>) or the <i>pmrA</i> (<i>G211</i>) allele in the presence of the antibiotic polymyxin B (2.5 µg/ml) on plates containing 10 µM Mg²⁺ and 100 µM Fe³⁺. <i>S. paratyphi</i> B growth was determined in the wild-type (SARA46), in a strain harboring either the <i>pmrA</i> (<i>E211</i>) (DC282) or <i>pmrA</i> (<i>G211</i>) (DC280) gene, in a Δ<i>pmrD</i> mutant expressing the <i>pmrA</i> (<i>E211</i>) (DC165 and DC287) or <i>pmrA</i> (<i>G211</i>) gene (DC285), and in a Δ<i>pmrA</i> mutant (DC167) (C). As a control, growth of <i>S. typhimurium</i> 14028s was monitored on the same plate (C). <i>S. typhimurium</i> growth was determined in the wild-type (14028s), in a strain harboring a 3′ FLAG-tagged <i>S. typhimurium pmrD</i> gene and the <i>pmrA</i> (<i>E211</i>) (EG16279) or <i>pmrA</i> (<i>G211</i>) (EG13404) allele, in a Δ<i>pmrD</i> mutant expressing the <i>pmrA</i> (<i>E211</i>) (DC46) or <i>pmrA</i> (<i>G211</i>) (EG14088) gene, and in a <i>pmrA</i> mutant (EG7139) (D).