Abstract
Staphylococcus aureus strain Newman was investigated for changes in its growth pattern, its morphology and its viability when grown in the presence of 3 microg/ml florfenicol (Ff). This concentration corresponds to the 0.75-fold strain-specific minimum inhibitory concentration (MIC). Under these conditions, S. aureus Newman showed a distinct retardation in its growth pattern and 20% dead cells were detected in a fluorescence microscopic viability assay. However, bactericidal activity - defined as a 3-log drop in the staphylococcal population - was not recorded at this Ff concentration. Further analysis of the cell wall revealed a significant increase in cell wall thickness of S. aureus Newman when grown in the presence of 3 microg/ml Ff. This might result in a compression of the protoplast with subsequent disruption of single staphylococcal cells. Accordingly, 20% of the staphylococcal cells analysed by electron microscopy proved to be disrupted. These observations suggest that Ff can cause a thickening of the cell wall accompanied by impaired viability of the staphylococcal cells.
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