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Title: COMPARISON OF SCANNING ELECTRON AND ATOMIC FORCE MICROSCOPY OF SURFACE FINISHES ON STAINLESS STEEL THAT REDUCE BACTERIAL ATTACHMENT

Author
item ARNOLD, JUDY
item BAILEY, G. - EPA

Submitted to: Scanning
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/21/2000
Publication Date: 4/30/2000
Citation: ARNOLD, J.W., BAILEY, G.W. COMPARISON OF SCANNING ELECTRON AND ATOMIC FORCE MICROSCOPY OF SURFACE FINISHES ON STAINLESS STEEL THAT REDUCE BACTERIAL ATTACHMENT. SCANNING. 2000.

Interpretive Summary: The use of surface materials that are resistant to bacteria could enhance food safety. Two methods of microscopy were partnered in a novel way to compare the structure and functionality of surfaces. Differences in the structure of surfaces were measured by atomic force microscopy (AFM) and compared with changes in bacterial attachment and early biofilm formation shown by scanning electron microscopy (SEM). For AFM, treated stainless steel disks were examined, and measurements were made such as surface roughness, bearing ratio, and center line average. For SEM, samples of meat rinses were incubated in broth overnight to culture bacteria. Then the disks were added, and the cultures were incubated to allow time for bacteria to attach. The disks were removed from the cultures and processed. Bacteria readily attached to untreated steel. Sandblasting pitted the surface, and formed microscopic "craters" to which bacteria attached even more frequently. The steel-ball burnished surface was much smoother, but was not the least resistant to bacteria. Electropolished steel showed significantly fewer bacterial cells than other treatments. Changes in the structure were related to the bacterial counts, with the electropolished finish showing the most reduced roughness parameters. Partnering the microscopy methods provides useful data on materials for equipment manufacturers and processors.

Technical Abstract: The use of surface materials that are resistant to bacterial contamination could enhance food safety in processing facilities. Two methods of microscopy were partnered in a novel way to correlate form and function of surface finishes. Differences in the morphology of surface finishes were measured by atomic force microscopy (AFM) and compared with bacterial attachment and biofilm formation shown by scanning electron microscopy (SEM). For AFM, stainless steel disks were examined directly. Dimensions were measured for surface roughness, bearing ratio, & center line average. For SEM, aliquots (1- ml) of meat rinses were incubated in trypticase soy broth 18 hr, 37C. The culture was diluted in broth to Absorbance (410nm) of .3. Disks (1-cm diameter) were added, and the cultures were grown to .6, 37C. Then the disks were removed and processed. Bacteria readily attached to untreated steel. Sandblasting pitted the surface, and with SEM the pit-marks seen by visual observation appeared as "craters" to which bacteria attached even more frequently. The steel-ball burnished surface was much smoother, but was not the least resistant to bacteria. Stainless steel that had been electropolished showed significantly fewer bacterial cells than the other treated surfaces. Changes in the AFM parameters had the same relative differences as the data from the bacterial counts for the SEM studies, with the electropolished finish showing the most reduced roughness parameters. Partnering the microscopy methods provides useful data on materials for processing equipment manufacturers and processors.