Surface roughness enhances upward migration of bacteria on polymer fibers above liquid cultures

Monofilament polypropylene (PP) fibers, very similar to fibers that have been used as monofilament tailstrings of interuterine contraceptive devices, were suspended vertically in bacterial liquid monocultures so that a portion of a fiber extended above the liquid surface. In some cases these highly oriented, cold drawn fibers were abraded prior to insertion in the cultures in order to produce surface roughness characterized by axial channels and protruding microfibrils that partially peeled from the fiber surface thereby forming the channels. Extent of migration on a fiber was assessed by aseptically cutting it into small segments, followed by culturing each segment on agar containing growth medium. Such assessment of the PP fibers after 48 h of incubation in the cultures revealed upward migration of Eschericia coli, Pseudomonas aeruginosa, and Staphylococcus aureus over significantly longer distances on the pre-roughened fibers than on those not so pre-treated. Mean measured distances of migration during 48 h were: for E. coli 2.7+/-0.6 mm on roughened fibers (n = 16) and 0.4+/-0.7 mm on fibers not roughened (n = 17); for S. aureus 9.0+/-4.3 mm on roughened fibers (n = 13) and 0.2+/-0.3 mm on fibers not roughened (n = 14); for P. aeruginosa 8.5+/-3.7 mm on roughened fibers (n = 26) and 0.2+/-0.5 mm on fibers not roughened (n = 5). Although no statistically significant (95% confidence level) difference could be discerned between the migration distances of S. aureus and P. aeruginosa, each of these species migrated a greater distance on the PP than did E. coli. The migrations observed are attributed predominantly to wicking of the liquid cultures upward in the axial grooves developed on the surface of the PP by the eruption and peeling of microfibrils from the surface. Surface tension of the growth medium was significantly lower than that of water and its contact angle on PP was less than 90 deg, thereby indicating a tendency to wet the PP. Bacterial growth in the medium further reduced its contact angle on PP, thereby indicating an even greater tendency to wet PP after such growth.