Extracellular DNA-induced antimicrobial peptide resistance in Salmonella enterica serovar Typhimurium

BMC Microbiology

Shawn Lewenza²  Michael G Surette¹  Heidi Mulcahy²  Amy L Turnbull²  Laetitia Charron-Mazenod²  Shawn R Horsman²  Lori Johnson² 

[1]Department of Medicine, Farncombe Family Digestive Health Research Institute, Health Sciences Centre, McMaster University, Rm 3N6-9, 1280 Main Street West, Hamilton, ON, L8S 4K1, Canada

[2]Department of Microbiology, Immunology and Infectious Diseases, University of Calgary, HRIC Building, Room 2C66, 3330 Hospital Drive NW, Calgary, AB, T2N 4N1, Canada

关键词: Immune evasion;    Biofilms;    Extracellular DNA;    Antibiotic resistance;    Antimicrobial peptides;    pmrAB;    phoPQ;    Salmonella;   

Others  :  1143692
DOI  :  10.1186/1471-2180-13-115

 received in 2013-01-23, accepted in 2013-05-17,  发布年份 2013

【 摘 要 】

Background

The Salmonella enterica serovar Typhimurium PhoPQ two component system (TCS) is activated by low Mg²⁺ levels, low pH and by antimicrobial peptides (AP). Under Mg²⁺ limitation, the PhoPQ system induces pmrD expression, which post-translationally activates the PmrAB TCS. PhoPQ and PmrAB control many genes required for intracellular survival and pathogenesis. These include the polymyxin resistance (pmr) operon, which is required for aminoarabinose modification of LPS and protecting the outer membrane from antimicrobial peptide disruption and killing. Extracellular DNA is a ubiquitous polymer in the matrix of biofilms and accumulates in some infection sites. Extracellular DNA chelates cations and thus activates the Pseudomonas aeruginosa PhoPQ/PmrAB systems, leading to expression of the orthologous arn (pmr) operon.

Results

Here we show that extracellular DNA induces expression of the S. Typhimurium pmr antimicrobial peptide resistance operon in a PhoPQ and PmrAB-dependent manner. Induction of the pmr genes by DNA was blocked when present with excess Mg²⁺. Exogenous DNA led to increased resistance of planktonic cultures to aminoglycosides, antimicrobial peptides (AP) and ciprofloxacin, but only AP resistance was PhoPQ/PmrAB-dependent. Extracellular DNA was shown to be a matrix component of S. Typhimurium biofilms cultivated in flow chambers and on glass surfaces. A pmrH-gfp fusion was highly expressed in flow chamber biofilms cultivated in medium with repressing levels of 10 mM Mg²⁺ and co-localized with eDNA. Expression of pmrH-lux was monitored in plastic peg biofilms and shown to require PhoPQ and PmrAB. Biofilms had higher levels of pmrH expression compared to planktonic cultures. We propose that DNA accumulation in biofilms contributes to the increased pmrH-lux expression in biofilms.

Conclusions

The Salmonella PhoPQ/PmrAB systems and antimicrobial peptide resistance are activated by the cation chelating properties of extracellular DNA. DNA-induced AP resistance may allow immune evasion and increased survival of S. Typhimurium biofilms formed during extracellular growth stages of an infection or outside the host.

【 授权许可】

   
2013 Johnson et al.; licensee BioMed Central Ltd.

【 图 表 】

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