PmrA–PmrB‐regulated genes necessary for 4‐aminoarabinose lipid A modification and polymyxin resistance

Abstract

SummaryAntimicrobial peptides are distributed throughout the animal kingdom and are a key component of innate immunity. Salmonella typhimurium regulates mechanisms of resistance to cationic antimicrobial peptides through the two-component systems PhoP-PhoQ and PmrA-PmrB. Polymyxin resistance is encoded by the PmrA-PmrB regulon, whose products modify the lipopolysaccharide (LPS) core and lipid A regions with ethanolamine and add aminoarabinose to the 4Ј phosphate of lipid A. Two PmrA-PmrB-regulated S. typhimurium loci (pmrE and pmrF ) have been identified that are necessary for resistance to polymyxin and for the addition of aminoarabinose to lipid A. One locus, pmrE, contains a single gene previously identified as pagA (or ugd ) that is predicted to encode a UDP-glucose dehydrogenase. The second locus, pmrF, is the second gene of a putative operon predicted to encode seven proteins, some with similarity to glycosyltransferases and other complex carbohydrate biosynthetic enzymes. Genes immediately flanking this putative operon are also regulated by PmrAPmrB and/or have been associated with S. typhimurium polymyxin resistance. This work represents the first identification of non-regulatory genes necessary for modification of lipid A and subsequent antimicrobial peptide resistance, and provides support for the hypothesis that lipid A aminoarabinose modification promotes resistance to cationic antimicrobial peptides.

An Undecaprenyl Phosphate-Aminoarabinose Flippase Required for Polymyxin Resistance in Escherichia coli

“…After transport to the outer surface of the inner membrane, presumably by ArnE (PmrL) and ArnF (PmrM) as shown in the present study, the membrane enzyme ArnT (31) transfers the L-Ara4N moiety to lipid A. B, order of genes and direction of transcription (left to right) of the pmr operon (16). The preferred arn terminology (2,45), which is consistent with the generalized bacterial polysaccharide gene nomenclature (94), is shown in red.…”

“…2B and Table 2. The pmr designations (11,12,16) were originally used to describe genes required for the maintenance of polymyxin resistance in S. typhimurium (Fig. 2B).…”

“…2B) (16), which display distant sequence similarity to the multidrug efflux pump exporter EmrE (37)(38)(39). In-frame chromosomal deletion mutants of pmrL and pmrM, generated in a polymyxin-resistant pmrA c parental strain, regain polymyxin sensitivity.…”

Proteomic analysis of Pseudomonas aeruginosa grown under magnesium limitation

“…PhoP orthologues regulate expression of genes essential for virulence and magnesium acquisition in several Gram-negative bacteria [14,20,11]. Some of the PhoP-induced enzymes promote increased bacterial resistance to antimicrobial peptides, a key component of host's innate immunity [10,17,21,22]. For example, PhoP-activated LPS modifications, including the addition of aminoarabinose and palmitate to lipid A, promote resistance to the antibiotic polymyxin and other cationic antimicrobial peptides [10,21,23].…”

“…Some of the PhoP-induced enzymes promote increased bacterial resistance to antimicrobial peptides, a key component of host's innate immunity [10,17,21,22]. For example, PhoP-activated LPS modifications, including the addition of aminoarabinose and palmitate to lipid A, promote resistance to the antibiotic polymyxin and other cationic antimicrobial peptides [10,21,23]. Consistent with the addition of aminoarabinose to LPS, homologues of S. enterica enzymes necessary for aminoarabinose addition and resistance to polymyxin (PA3552-3554) were among the most highly induced proteins in this study (Table 2).…”