Transmission of Monospecies and Dual-Species Biofilms from Smooth to Nanopillared Surfaces

The transmission of bacteria in biofilms from donor to receiver surfaces precedes the formation of biofilms in many applications. Biofilm transmission is different from bacterial adhesion, because it involves biofilm compression in between two surfaces, followed by a separation force leading to the detachment of the biofilm from the donor surface and subsequent adhesion to the receiver surface. Therewith, the transmission depends on a balance between donor and receiver surface properties and the cohesiveness of the biofilm itself. Here, we compare bacterial transmission from biofilms of an extracellular-polymeric-substance (EPS)-producing and a non-EPS-producing staphylococcal strain and a dual-species oral biofilm from smooth silicon (Si) donor surfaces to smooth and nanopillared Si receiver surfaces. Biofilms were fully covering the donor surface before transmission. However, after transmission, the biofilms only partly covered the donor and receiver surfaces regardless of nanopillaring, indicating bacterial transmission through adhesive failure at the interface between biofilms and donor surfaces as well as through cohesive failure in the biofilms. The numbers of bacteria per unit volume in EPS-producing staphylococcal biofilms before transmission were 2-fold smaller than in biofilms of the non-EPS-producing strain and of dual species. This difference increased after transmission in the biofilm left behind on the donor surfaces due to an increased bacterial density for the non-EPS-producing strain and a dual-species biofilm. This suggests that biofilms of the non-EPS-producing strain and dual species remained compressed after transmission, while biofilms of the EPS-producing strain were induced to produce more EPS during transmission and relaxed toward their initial state after transmission due to the viscoelasticity conferred to the biofilm by its EPS. IMPORTANCE Bacterial transmission from biofilm-covered surfaces to surfaces is mechanistically different from bacterial adhesion to surfaces and involves detachment from the donor and adhesion to the receiver surfaces under pressure. Bacterial transmission occurs, for instance, in food processing or packaging, in household situations, or between surfaces in hospitals. Patients admitted to a hospital room previously occupied by a patient with antibiotic-resistant pathogens are at elevated infection risk by the same pathogens through transmission. Nanopillared receiver surfaces did not collect less biofilm from a smooth donor than a smooth receiver, likely because the pressure applied during transmission negated the smaller contact area between bacteria and nanopillared surfaces, generally held responsible for reduced adhesion. Biofilm left behind on smooth donor surfaces of a non-extracellular-polymericsubstance (EPS)-producing strain and dual species had undergone different structural changes than an EPS-producing strain, which is important for their possible further treatment by antimicrobials or disinfectants.