Analysis of bacterial detachment from substratum surfaces by the passage of air-liquid interfaces

A theoretical analysis of the detachment of bacteria adhering to substratum surfaces upon the passage of an air-liquid interface is given, together wi th experimental results for bacterial detachment in the absence and presenc e of a conditioning film on different substratum surfaces. Bacteria (Strept ococcus sobrinus HG1025, Streptococcus oralis J22, Actinomyces naeslundii T 14V-J1, Bacteroides fragilis 793E, and Pseudomonas aeruginosa 974K) were fi rst allowed to adhere to hydrophilic glass and hydrophobic dimethyldichloro silane (DDS)-coated glass in a parallel-plate flow chamber until a density of 4 x 10(6) cells cm(-2) was reached. For S. sobrinus HG1025, S, oralis J2 2, and A. naeslundii T14V-J1, the conditioning film consisted of adsorbed s alivary components, while for S, fragilis 793E and P. aeruginosa 974K, the film consisted of adsorbed human plasma components, Subsequently, air bubbl es were passed through the Row chamber and the bacterial detachment percent ages were measured. For some experimental conditions, like with P. aerugino sa 974K adhering to DDS-coated glass and an air bubble moving at high veloc ity (i.e., 13.6 mm s(-1)), no bacteria detached upon passage of an air-liqu id interface, while for others, detachment percentages between 80 and 90% w ere observed, The detachment percentage increased when the velocity of the passing air bubble decreased, regardless of the bacterial strain and substr atum surface hydrophobicity involved, However, the variation in percentages of detachment by a passing air bubble depended greatly upon the strain and substratum surface involved. At low air bubble velocities the hydrophobici ty of the substratum had no influence on the detachment, but at high air bu bble velocities all bacterial strains were more efficiently detached from h ydrophilic glass substrata, Furthermore, the presence of a conditioning fil m could either inhibit or stimulate detachment, The shape of the bacterial cell played a major role in detachment at high air bubble velocities, and s pherical strains (i.e., streptococci) detached more efficiently than rod-sh aped organisms. The present results demonstrate that methodologies to study bacterial adhesion which include contact with a moving air-liquid interfac e (i.e., rinsing and dipping) yield detachment of an unpredictable number o f adhering microorganisms. Hence, results of studies based on such methodol ogies should be referred as "bacterial retention" rather than "bacterial ad hesion".