Contribution of SecDF to Staphylococcus aureusresistance and expression of virulence factors

Abstract

BackgroundSecDF is an accessory factor of the conserved Sec protein translocation machinery and belongs to the resistance-nodulation-cell division (RND) family of multidrug exporters. SecDF has been shown in Escherichia coli and Bacillus subtilis to be involved in the export of proteins. RND proteins can mediate resistance against various substances and might be of relevance in antimicrobial therapy. The role of RND proteins in Staphylococcus aureus has not yet been determined.ResultsMarkerless deletion mutants were constructed to analyze the impact of the so far uncharacterized RND proteins in S. aureus. While the lack of Sa2056 and Sa2339 caused no phenotype regarding growth and resistance, the secDF mutant resulted in a pleiotropic phenotype. The secDF mutant was cold sensitive, but grew normally in rich medium at 37°C. Resistance to beta-lactams, glycopeptides and the RND substrates acriflavine, ethidium bromide and sodium dodecyl sulfate was reduced. The secDF mutant showed an aberrant cell separation and increased spontaneous and Triton X-100 induced autolysis, although the amounts of penicillin-binding proteins in the membrane were unchanged. The impact of secDF deletion on transcription and expression of specific virulence determinants varied: While coagulase transcription and activity were reduced, the opposite was observed for the autolysin Atl. A reduction of the transcription of the cell wall anchored protein A (spa) was also found. The accumulation of SpA in the membrane and lowered amounts in the cell wall pointed to an impaired translocation.ConclusionsThe combination of different effects of secDF deletion on transcription, regulation and translocation lead to impaired cell division, reduced resistance and altered expression of virulence determinants suggesting SecDF to be of major relevance in S. aureus. Thus SecDF could be a potential target for the control and eradication of S. aureus in the future.

Extracellular protease in Actinomycetes culture supernatants inhibits and detaches Staphylococcus aureus biofilm formation

“…Proteolytic activity was determined using skim milk agar plates (Quiblier et al 2011) containing 5 g of non-fat dry milk and 0.5 g Bacto-agar (Difco) in 50 ml distilled water. To detect the extracellular protease activity, supernatants (10 ll) of Actinomycetes strains were added in a hole in the milk/agar plates and incubated at 37°C after 24 h. GSS medium (10 ll) and proteinase K (Sigma-Aldrich Co.) were used as negative and positive controls, respectively.…”

Antimicrobial Resistance and Virulence: a Successful or Deleterious Association in the Bacterial World?

“…In S. aureus, the SecDF system has been associated with impaired cell division, reduced resistance to the ␤-lactam oxacillin and to the glycopeptide vancomycin, and altered expression of virulence genes (atl, coa, hla, hld, and spa) (103).…”

Membrane Chaperone SecDF Plays a Role in the Secretion of Listeria monocytogenes Major Virulence Factors

“…For example, in E. coli the secDF mutant is characterized by a severe growth defect in rich laboratory medium at 30 and 37°C, yet it grows normally in glucose minimal defined medium at 37°C (31). In Bacillus subtilis and Staphylococcus aureus, secDF deletion mutants exhibit a cold-sensitive growth phenotype (at 15°C) but grow normally at 37°C (22,35). Notably, the cold sensitivity of the B. subtilis secDF mutant is exacerbated when the bacteria overexpress a secretory protein, yet this phenotype disappears if the bacteria are grown at 37°C (22).…”