No abstract

Transition from reversible to irreversible bacterial adhesion is a highly relevant but poorly understood step in initial biofilm formation. We hypothesize that in oral biofilm formation, irreversible adhesion is caused by bond strengthening due to specific bacterial interactions with salivary conditioning films. Here, we compared the initial adhesion of six oral bacterial strains to salivary conditioning films with their adhesion to a bovine serum albumin (BSA) coating and related their adhesion to the strengthening of the binding forces measured with bacteria-coated atomic force microscopy cantilevers. All strains adhered in higher numbers to salivary conditioning films than to BSA coatings, and specific bacterial interactions with salivary conditioning films were accompanied by stronger initial adhesion forces. Bond strengthening occurred on a time scale of several tens of seconds and was slower for actinomyces than for streptococci. Nonspecific interactions between bacteria and BSA coatings strengthened twofold faster than their specific interactions with salivary conditioning films, likely because specific interactions require a closer approach of interacting surfaces with the removal of interfacial water and a more extensive rearrangement of surface structures. After bond strengthening, bacterial adhesion forces with a salivary conditioning film remained stronger than those with BSA coatings.Oral biofilm ("dental plaque") formation proceeds according to a well-known sequence of events (7,18,19). The first step in this sequence is the adsorption of conditioning film components or, specified to the oral cavity, the adsorption of salivary components that form the acquired enamel pellicle, followed by bacterial transport to the substratum surface. Subsequently, bacteria initially (co)adhere (19) reversibly, after which a transition to an irreversible state sets in, and eventually the adhering bacteria start to grow and form a mature biofilm. The transition from reversible to irreversible adhesion is intriguing as it is largely unknown what actually happens during this transition. The transition is partly due to active bacterial processes such as anchoring through the excretion of extracellular polymeric substances (9). However, also inert polystyrene particles adhering to surfaces have demonstrated a transition from a reversible to a nearly irreversible state which has been attributed to (i) the progressive removal of interfacial water from in between the interacting surfaces, (ii) the reorientation of an adhering particle in order to face a substratum surface with its most favorable site, and (iii) conformational changes of protruding polymer chains (2,3,14). Using image sequence analysis (14, 15), it was found that the desorption probabilities of bacteria and polystyrene particles adhering to inert substrata decrease after their arrival at a surface within 30 to 60 s by a factor of 200 for bacteria and within 100 to 1,000 s by a factor of 100 for polystyrene particles.The change from a reversible to irreversi...

No abstract

Coadhesion between oral microbial pairs is an established factor in the spatiotemporal development and prevalence of mixed-species communities in early dental plaque in vivo. This study compares removal and de novo adhesion of pairs of coadhering and non-coadhering oral actinomyces and streptococci by sonic brushing on salivary pellicles in a non-contact mode as a function of the distance between the brush and the pellicle surface in vitro. First, actinomycetes were adhered to a pellicle surface, after which streptococci suspended in saliva were allowed to adhere. Removal was examined by non-contact, sonic brushing with a wetted brush on a either a wetted or a substratum immersed to a depth of 7 mm. After brushing, de novo adhesion of streptococci to brushed pellicles was studied. For coadhering and non-coadhering pairs, 34% and 9%, respectively, of the adhering bacteria were involved in aggregates comprising more than 10 organisms. Non-contact, sonic brushing removed up to 99% of the adhering bacteria, regardless of the state of immersion of the substratum. Bacterial removal decreased with increasing distance of up to 6 mm between brush and pellicle surface. For the non-coadhering pair, subsequent exposure of pellicles to a streptococcal suspension yielded about 6% of bacteria involved in large aggregates. Alternatively, de novo adhesion of the coadhering streptococcal strain to pellicles brushed on the wetted substratum yielded 31% of bacteria involved in large aggregates, but after brushing the immersed substratum only 12% of the adhering bacteria were found in large aggregates. It is concluded that non-contact sonic brushing, under immersion, removes high percentage of adhering bacterial pairs up to a distance of 6 mm between the brush and the pellicle surface. However, non-contact, sonic brushing with only a thin wet film on the substratum may leave footprints to which streptococci preferentially adhere.