Using an atomic force microscope to probe the surface of glass, mica, and quartz at the molecular level, Penn State engineers have, for the first time, identified the bacteria-sized peaks and valleys in this tiny terrain as an important factor in microbes1s ability to adhere to some of these materials.
Dr. Bruce E. Logan, the Kappe professor of environmental engineering, says, "Reducing bacterial adhesion is necessary for preventing tooth decay, the contamination of implants in humans, and the contamination of silicon chip surfaces during manufacture. On the other hand, it1s important to increase bacterial adhesion for the proper operation of water treatment filters and to limit pathogen migration in soil. Bacterial cell adhesion properties have been difficult to control, however, because we hadn1t sufficiently developed techniques to probe, study and describe the adhesion forces."
Logan explains that now, new forms of molecular-level microscopy have made it possible for the first time to scan both the individual microorganisms and the surfaces to which they attach and also to measure directly their topography and adhesion properties.
He and co-author Karl Shellenberger, a master1s degree candidate in environmental engineering, presented their findings Tuesday, Aug. 22, at the national meeting of the American Chemical Society in Washington, D. C., in a paper, "Probing Chemical-Microbiological Interactions Using Atomic Force Microscopy."
Using an atomic force microscope, it is possible to probe at the molecular level for charge distribution and to test the currently popular hypothesis that some sites on a particular surface are stickier than others because of a concentration of attractive or repulsive electric charge., he explains. Repeated scans of the surfaces of glass beads, mica, and glass slides showed no evidence of appreciably attractive or less repulsive areas on the order of the size of a bacterium or larger.
Logan says, "Our results do not support theories that electric charge differences result in favorable and unfavorable sites of attachment on these surfaces."
On the other hand, the researchers found that molecular scale surface roughness was important. In experiments, they controlled the size of the peak-and-valley surface protrusions on glass beads, leaving some the size of bacteria and smoothing others to smaller than a bacterium. Suspensions of bacteria and fluorescent microspheres were then passed through columns packed with either rough or smooth beads. The experiments showed that greater adhesion was produced with the molecularly-rough beads than with smooth beads.
"Traditionally, bacterial adhesion is described using theory which generally predicts less adhesion than found experimentally. New molecular-level tools such as atomic force microscopy, may make it possible to better predict and control these properties," Logan notes. The research was supported by a grant from the National Institute of Environmental Health Science.
EDITORS: Dr. Logan, is at 814-863-7908 or blogan@psu.edu by email.