Purpose: The aim of this study was to evaluate the biofilm-forming ability of C. sakazakii and Bacillus subtilis under mono- or mixed-culture conditions.
Methods: Biofilm formation was studied on stainless steel (SS) coupons utilizing a two-step procedure: SS coupons were initially incubated in saline bacterial suspensions at 15°C for 3 h (attachment step) and afterwards, coupons carrying strongly attached bacteria were further incubated at 37°C for 72 h or at 20°C for 144 h. Viable biofilm bacterial populations were determined, using the bead vortexing method, after initial attachment, and at 24-h and 48-h intervals during incubation at 37°C and 20°C, respectively.
Results: Biofilm formation was found to be influenced by time, bacterial species and culture conditions (mono- or mixed-culture). Regarding the mono-culture conditions, B. subtilis exhibited a significantly (P<0.05) lower biofilm formation compared to C. sakazakii for the first 48 h of incubation at 20°C. Co-culture with B. subtilis within a dual-species community significantly (P<0.05) enhanced the biofilm-forming ability of C. sakazakii at 37°C; nonetheless, no corresponding difference was observed with regard to biofilm formation at 20°C.
Significance: Multi-species biofilms are dynamic systems with variable interactions among the different species, and the above results reinforce the aspect that bacteria have developed different strategies to adapt to environmental conditions and exist within biofilm communities.