Nutrient limitation affects growth and attachment of two food spoilage bacteria, Bacillus subtilis and Pseudomonas fluorescens

The attachment was studied of the food spoilage bacteria Pseudomonas (P.) fluorescens and Bacillus (B.) subtilis to stainless steel test surfaces suspended in Minimal Salts Medium (MSM) or Standard One Nutrient Broth (SONB). Attached cells were enumerated on Standard One Nutrient Agar after being dislodged from test surfaces by being shaken with beads. Counts of planktonic cells grown in SONB and MSM were evaluated in parallel with counts of attached cells. Higher counts of attached P. fluorescens and B. subtilis cells (c. 1 log cfu cm(-2)) were recovered from surfaces suspended in SONB compared to those in MSM. Counts of planktonic B. subtilis cells grown in SONB exceeded those in MSM by c. 1 log cfu ml(-1). By contrast, counts of planktonic P. fluorescens in SONB and MSM were not significantly different (P > 0.05). Scanning electron microscopy showed attached cells of B. subtilis grown in SONB to be rod-shaped, while coccoid shapes were observed for corresponding cells grown in MSM. Attached cells of P. fluorescens were rod-shaped in both SONB and MSM. Evidence of extracellular polymeric substance formation was observed for attached cells of both bacteria in SONB and MSM. These findings have implications for the contamination of foodstuffs by these bacteria.