Influence of a medium pH and ionic strength on the adhesion of Streptococcus thermophilus microorganisms to human erythrocytes

Abstract

Background and Purpose: Diseases caused by bacterial pathogens are the result of the host-pathogen interaction, therefore the contact of bacteria with erythrocytes is highly possible. The aim of this work was to study Streptococcus thermophilus adhesion on human erythrocytes depending on the various pH and ionic strength of the medium. Materials and Methods: Streptococcus thermophilus bacterial cells and human red blood cells have been selected. Erythrocytes were washed with buffer saline and precipitated by centrifugation. Dried bacterial cells were suspended, incubated, washed in buffer saline and precipitated. The precipitate of both types of cells was resuspended in 1:2 ratio in a buffer solution with different physicochemical characteristics. The number of bacteria adhered to each erythrocyte has been counted under light microscope in each field of view and adhesion coefficient has been calculated. Results: Adhesion coefficient is strongly dependent on pH of the medium and reaches maximum at physiological pH for red blood cells. Data for the other examined pH values probabilistically differ at the same confidence level. Adhesion index was the highest in physiological saline (2.21 ± 0.87). Both increase or decrease in the ionic strength (0.2 M salt) resulted in the drop of adhesion rate, it becomes minimal (0.95 ± 0.63) in the medium with the lowest investigated ionic strength (0.25 M sucrose, 0.025 M salt). Conclusions: The results of our experiments indicate that adhesion proceeds through initial nonspecific stage which plays an important role in the adhesion process and affects the possibility of the second irreversible stage of adhesion.