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 micros copy, and confocal scanning laser microscopy were used to study the physiol ogy of Staphylococcus aureus in the early stages of surface-attached cultur e, and to make direct comparisons with planktonic bacteria grown under the same conditions. Attached bacteria growing in nutrient-rich batch culture w ere found to go through the same growth phases as equivalent planktonic cul tures, but with an exponential growth rate of about half that of the plankt onic bacteria. Viability of attached bacteria was very high (around 100 %) throughout the first 24 h of growth. The sire and protein content of attach ed bacteria varied with growth phase, sind both measurements were always sm aller 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 c ell division) and declined from then on, whereas in planktonic bacteria it peaked in late exponential phase. Attached and planktonic bacteria showed t hicker cell walls in stationary phase than in exponential phase. Membrane p otentials of planktonic and attached bacteria were similar in stationary ph ase, but were much lower in exponential-phase attached cells than in the eq uivalent planktonic cells. It is apparent that a range of significant physi ological adaptations occur during the early phases of attached growth.