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Molecular basis of florfenicol-induced increase in adherence of Staphylococcus aureus strain Newman
Maren Blickwede1, Ralph Goethe, Christiane Wolz
1Institut für Tierzucht, Bundesforschungsanstalt für Landwirtschaft (FAL), Höltystrasse 10, 31535 Neustadt-Mariensee, Germany.
Objectives:
The aim of this study was to determine the molecular basis of the florfenicol-dependent increased adherence of Staphylococcus aureus strain Newman to HEp-2 cells.
Methods And Results:
Northern slot blot analysis showed that mRNA expression of fnbA, fnbB, coa, emp and eap, coding for adhesins, was increased in the presence of 0.5 x MIC of florfenicol. Under the same conditions expression of cap5, coding for type 5 capsular polysaccharides, was distinctly decreased. Since global regulatory systems can modulate the expression of adhesins, their role in this process was investigated by including three isogenic mutants with functionally inactive global regulator systems, agr, sar or sae. Growth in the presence of 0.5 x MIC of florfenicol significantly increased the adherence to HEp-2 cells, fibronectin and fibrinogen of the Deltaagr and Deltasar mutant strains, but not that of the Deltasae mutant strain. In contrast to components of the agr or sar system, expression of saeRS was increased, suggesting a potential sae-directed decrease in the expression of cap5 and increase in the expression of genes coding for adhesins under the influence of florfenicol. Analysis of RNA stability revealed that the increased amount of transcripts of saeRS and adherence-associated genes was due to a stabilization of the respective mRNAs by florfenicol.
Conclusions:
Our data provide evidence that an activation of the global regulator sae and a stabilization of mRNA coding for specific adhesins seem to act synergically in generating a more adherent phenotype in the presence of a high subinhibitory concentration of florfenicol.
Insights
Florfenicol increases Staphylococcus aureus adherence by stabilizing adhesin mRNA and activating the sae global regulator. This leads to a more adherent bacterial phenotype, particularly in agr and sar mutants.
Area of Science:
- Microbiology
- Molecular Biology
- Bacterial Pathogenesis
Background:
- Staphylococcus aureus adherence to host cells is crucial for infection.
- The antibiotic florfenicol can modulate bacterial virulence factors.
- Global regulatory systems (agr, sar, sae) control S. aureus gene expression.
Purpose of the Study:
- To elucidate the molecular mechanisms behind florfenicol-induced adherence of S. aureus Newman to HEp-2 cells.
- To investigate the role of global regulators (agr, sar, sae) in this florfenicol-mediated effect.
Main Methods:
- Northern slot blot analysis to assess mRNA expression of adhesins and capsular polysaccharides.
- Utilizing isogenic mutants (Deltaagr, Deltasar, Deltasae) to study regulatory systems.
- RNA stability assays to determine transcript half-lives.
Main Results:
- Florfenicol (0.5 x MIC) upregulated mRNA for adhesins (fnbA, fnbB, coa, emp, eap) and downregulated capsular polysaccharide (cap5) expression.
- Adherence to HEp-2 cells, fibronectin, and fibrinogen increased in Deltaagr and Deltasar mutants but not Deltasae mutant under florfenicol exposure.
- Florfenicol exposure increased saeRS expression and stabilized mRNAs for saeRS and adhesin-associated genes.
Conclusions:
- Activation of the sae global regulator and mRNA stabilization of adhesins synergistically enhance S. aureus adherence.
- High subinhibitory concentrations of florfenicol promote a more adherent bacterial phenotype through specific molecular pathways.
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