The pmrHFIJKLM operon is directly regulated by PmrAB, is induced during phagocytosis and is required for survival from host antimicrobial peptide production [16]. The pmr operon encodes

an LPS modification system that is responsible for aminoarabinose modification of the lipid A moiety of LPS. Reducing the negative charge of the bacterial surface with aminoarabinose is critical for MRT67307 research buy reducing the membrane damaging effects of cationic antimicrobial peptides. We recently demonstrated that DNA is a cation chelator that induces expression of the Pseudomonas aeruginosa arnBCADTEF-ugd (PA3552-PA3559; pmr) operon in DNA-enriched planktonic cultures and biofilms [17]. DNA sequesters cations and creates a condition that resembles a Mg2+-limited environment, similar to known chelators like EDTA. Expression of this operon was required for very high levels of biofilm resistance to antimicrobial peptides and partially contributed to aminoglycoside resistance [17]. During Mg2+ limiting growth conditions, the P. aeruginosa PhoPQ and PmrAB systems are both required for expression of the arn operon [18, 19]. Both the PhoPQ and PmrAB systems respond to this website Mg2+ limitation in P. aeruginosa, and there is no PmrD ortholog to connect the two pathways. In addition, the P. aeruginosa PhoQ sensor does not directly detect antimicrobial peptides, and the PmrB sensor does not respond to trivalent metals [18]. Extracellular DNA also induces the expression

of PmrAB-regulated spermidine synthesis genes, which results in the production of the polycation spermidine on the surface and protection of the outer membrane from antimicrobial peptide treatment [20]. Both the arn and spermidine synthesis (PA4773-PA4775) clusters were induced

in biofilms Go6983 order formed by a bfmR mutant of P. aeruginosa that accumulated more eDNA than wild-type biofilms [21]. When sufficient DNA accumulates in P. aeruginosa biofilms, or in the cystic fibrosis (CF) lung where the concentration of DNA is very high and leads to viscous sputum production in CF patients [22, 23], the expression of these DNA-induced surface modifications likely protect from host antimicrobial peptide killing. Therefore, we wanted to determine if extracellular DNA plays a general role in learn more antimicrobial peptide resistance by imposing a cation limitation on S. Typhimurium biofilms and activating the PhoPQ/PmrAB systems, similar to P. aeruginosa. Results and discussion Extracellular DNA induces expression of the Salmonella pmr operon A low copy, plasmid-encoded transcriptional lux fusion to the pmrH promoter [24] was expressed in Salmonella enterica serovar Typhimurium 14208 under various planktonic growth conditions. At pH 7.4, the pmrH-lux reporter was repressed at 1 mM Mg2+ but was induced 13-fold in a stepwise fashion as the Mg2+ concentration was decreased to 0.06 mM (Figure  1A). The pmrH-lux fusion was most highly expressed under low pH (5.5) (Figure  1B), even with the addition of up to 50 mM Mg2+ (data not shown).