The role of physicochemical and structural surface properties in co-adhesion of microbial pairs in a parallel-plate flow chamber

Real-time quantification of Pseudomonas fluorescens cell removal from glass surfaces due to bacteriophage varphiS1 application

AIMS

To study the efficacy of the lytic phage varphiS1 in eliminating Pseudomonas fluorescens in the early stage of biofilm formation, using an in situ and real time methodology for cell quantification.

METHODS AND RESULTS

Cell adhesion and phage infection studies were carried out in a parallel plate flow chamber under laminar conditions. Cells were allowed to adhere until reaching 1.7-1.8 x 10(6) cells cm(-2) and phage infection was performed with two different phage concentrations (2 x 10(9) PFU ml(-1) and 1 x 10(10) PFU ml(-1)). Phage concentration clearly affects the speed of infection. The less concentrated phage solution promoted a three times slower rate of cell removal but did not affect the overall percentage of cell removal. In fact, after a longer infection period the less concentrated phage solution reached the same 93% cell removal value.

CONCLUSIONS

Phages are efficient in the eradication of bacterial cells at the early stage of biofilm formation and their presence at the surface did not allow bacterial recolonization of the surface.

SIGNIFICANCE AND IMPACT OF THE STUDY

To date, no published studies have been made concerning in situ and real time quantification of cell removal from surfaces due to phage action.

Interactive forces between co-aggregating and non-co-aggregating oral bacterial pairs

The temporo-spatial development of plaque is governed by adhesive interactions between different co-aggregating bacterial strains and species. Physico-chemically, these interactions are due to attractive Lifshitz-Van der Waals and acid-base forces, and occur despite electrostatic repulsion and with a critical influence of temperature. The forces between co-aggregating and non-co-aggregating pairs have never been measured, however. The aim here, thus, is to investigate, by atomic force microscopy, whether there is a difference in interactive forces between co-aggregating and non-co-aggregating bacterial pairs at 10 degrees C, 22 degrees C, and 40 degrees C. Actinomyces naeslundii 147 was immobilized on poly-L-lysine-coated tipless AFM cantilevers, while streptococci were immobilized on poly-L-lysine-coated glass surfaces. Upon approach, a repulsive force was measured, regardless of whether a co-aggregating or non-co-aggregating pair was involved. However, upon retraction, the co-aggregating pair exhibited larger adhesive forces and energies than did the non-co-aggregating pair. Adhesive interactions between the co-aggregating pair were smallest at 40 degrees C.

Path-dependency of the interaction between coaggregating and between non-coaggregating oral bacterial pairs--a thermodynamic approach

Coaggregation, i.e. specific recognition between bacteria from different species, is a well-described phenomenon in the human oral cavity but remains physically poorly understood. With our study we aimed at elucidating some aspects of the mechanism of the coaggregation between the oral bacteria Streptococcus oralis J22 and Actinomyces naeslundii 147, in particular with respect to the driving force for coaggregation and its pathway-dependency. To that end, the macroscopic turbidity of the bacterial suspension, the morphology of the coaggregates, binding isotherms and heats of interaction were compared between the above-mentioned coaggregating bacterial pair and a non-coaggregating pair, Streptococcus sanguis PK1889 and A. naeslundii 147. The coaggregating pair forms large aggregates, which rapidly sediment from the suspension while the non-coaggregating pair forms only very small coaggregates that remain homogeneously suspended. Coaggregation is further characterized by a high affinity between the partner cells that bind to each other in a strong cooperative mode. The interactions between both pairs occur under the release of heat and are thus enthalpically favorable. More heat is released for the coaggregating than for the non-coaggregating pair. Adding the coaggregating bacteria in steps to each other leads to saturation of enthalpically favorable binding sites. This is observed when the streptococcus is added to the actinomyces as well as when the addition is done the other way around. It is concluded that the cooperativity of the coaggregation process is based on an increase of entropy. It is furthermore shown that the density of the coaggregates as well as the heat effect of formation of these coaggregates depend on the number of steps in which the partner cells are added to each other. Adding S. oralis J22 in three steps to A. naeslundii 147 results in the formation of denser coaggregates under the release of less heat, as compared to that of addition in one step. These differences point to a larger entropy increase when in a step-wise mixing the coaggregating bacteria are allowed to form more densely-packed coaggregates.

Adhesive interactions between medically important yeasts and bacteria

Yeasts are being increasingly identified as important organisms in human infections. Adhesive interactions between yeasts and bacteria may contribute to yeast retention at body sites. Methods for studying adhesive interactions between bacterial strains are well known, and range from simple macroscopic methods to flow chamber systems with complex image analysis capabilities. The adhesive interactions between bacteria and yeasts have been studied employing several of the methods originally developed for studying adhesive interactions between bacteria. However, in many of the methods employed the larger size of the yeasts as compared with bacteria results in strong sedimentation of the yeasts, often invalidating the method adapted. In addition, most methods are semi-quantitative and do not properly control mass transport. Consequently, adhesive interaction mechanisms between yeasts and bacteria identified hitherto, including lectin binding and protein-protein interactions, must be regarded with caution. Extensive physico-chemical characteristics of yeast cell surfaces are not available and a physico-chemical mechanism has not yet been put forth. A new method for quantifying adhesive interactions between yeasts and bacteria is proposed, based on the use of a parallel plate flow chamber, in which the influence of adhering bacteria upon the kinetics of yeast adhesion and aggregation of the adhering yeasts is quantitatively evaluated, under carefully controlled mass transport.

Physico-chemical interactions in initial microbial adhesion and relevance for biofilm formation

This paper summarizes initial microbial adhesion events in dental plaque formation, including the physico-chemistry of the interaction between micro-organisms and solid substrata, detachment phenomena under the fluctuating shear of the oral cavity, co-adhesion between pairs of microbial strains, and biosurfactant release. A hypothesis is forwarded on how these initial events might influence the final microbial composition and structure of the plaque, although it is simultaneously emphasized that the necessary techniques for verification of the hypothesis have only recently become available, and supporting evidence is still to be collected.