Flow cytometry and other techniques show that Staphylococcus aureus undergoes significant physiological changes in the early stages of surface-attached culture

The techniques of flow cytometry, scanning and transmission electron microscopy, and confocal scanning laser microscopy were used to study the physiology of Staphylococcus aureus in the early stages of surface-attached culture, and to make direct comparisons with planktonic bacteria grown under the same conditions. Attached bacteria growing in nutrient-rich batch culture were found to go through the same growth phases as equivalent planktonic cultures, but with an exponential growth rate of about half that of the planktonic bacteria. Viability of attached bacteria was very high (around 100%) throughout the first 24 h of growth. The size and protein content of attached bacteria varied with growth phase, and both measurements were always smaller than in planktonic bacteria at equivalent growth phases. Respiratory activity per bacterium, as measured by flow cytofluorimetry, and corrected for cell volume, peaked very early in attached cultures (before the first cell division) and declined from then on, whereas in planktonic bacteria it peaked in late exponential phase. Attached and planktonic bacteria showed thicker cell walls in stationary phase than in exponential phase. Membrane potentials of planktonic and attached bacteria were similar in stationary phase, but were much lower in exponential-phase attached cells than in the equivalent planktonic cells. It is apparent that a range of significant physiological adaptations occur during the early phases of attached growth.