Influence of milk proteins on the adhesion and formation of Bacillus sporothermodurans biofilms: Implications for dairy industrial processing

Bacillus sporothermodurans is a producer of highly heat-resistant spores, which is a problem for the dairy industry worldwide. In this work, we studied the attachment and biofilm formation on stainless steel surfaces in contact with milk proteins (casein and whey). The results of the biofilm formation were obtained by the plate count method. In conjunction, biofilms (niches and cell sizes) were measured by scanning electron microscopy (SEM) on the 1st, 5th and 10th day. X-ray photoelectron spectroscopy (XPS) was a complementary technique that probed the conditioning of the substrate surface after 24 h. The milk proteins affected the total bacterial count in the samples, and also influenced the biofilm architecture. Sessile cell counts varied from 4.3 log CFU/cm2 in the attachment stage to up to 10.2 log CFU/cm2 in the matured biofilm stage. The spore counts varied from <1.4 ± 0.02 (1st day) to 3.7 log ± 1.1 log spores/cm2 (10th day). The control group at the biofilm maturation stage (5th day) had higher niches than at the cell fixation (1st day) and was different from the other groups that showed active dispersion in the presence of milk proteins. The same occurred on the 10th day for the control group. Circular patterns in the biofilm with casein, passive dispersal and elongated cells were also observed. Enzyme treatment and disinfectants may be used to remove or reduce biofilm formation.