JAC Advance Access originally published online on June 27, 2005
Journal of Antimicrobial Chemotherapy 2005 56(2):315-323; doi:10.1093/jac/dki233
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Molecular basis of florfenicol-induced increase in adherence of Staphylococcus aureus strain Newman
1 Institut für Tierzucht, Bundesforschungsanstalt für Landwirtschaft (FAL), Höltystrasse 10, 31535 Neustadt-Mariensee; 2 Institut für Mikrobiologie, Zentrum für Infektionsmedizin, Tierärztliche Hochschule Hannover, Bischofsholer Damm 15, 30173 Hannover; 3 Institut für Medizinische Mikrobiologie und Hygiene, Universität Tübingen, Wilhelmstrasse 31, 72074 Tübingen, Germany
Received 8 December 2004; returned 9 May 2005; revised 19 May 2005; accepted 3 June 2005
* Corresponding author. Tel: +49-5034-871-241; Fax: +49-5034-871-246; E-mail: stefan.schwarz{at}fal.de
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 
agr and sar mutant strains, but not that of the sae 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.
Keywords: fibronectin , fibrinogen , capsule , RNA stability , HEp-2 cells
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