Interaction of Pseudomonas putida and Listeria monocytogenes in mixed culture biofilms / by Greg Kepka.

Abstract

"Listeria monocytogenes is a foodborne pathogen that causes problems in many food processing plants because it produces biofilms and thus is difficult to control by regular cleaning and sanitizing procedures. It has been stated that the growth of L. monocytogenes is enhanced in mixed culture biofilms, but little information is available that provides a mechanistic explanation for this. Mixed culture biofilms with Pseudomonas putida (labeled with green fluorescent protein) and L. monocytogenes EGD were examined to determine whether one organism would enhance growth of the other. Mono and mixed culture biofilms were grown on glass cover slips, in M9 1x minimal salt medium supplemented with 1mM glucose at 22C for 24 hours using a flow cell. Images were taken using a scanning electron microscope and with a confocal scanning laser microscope, after staining Listeria cells with a Texas Red-X conjugate of wheat germ agglutinin. Confocal images captured at inlet, middle and outlet of the flow cell were analyzed with the novel biofilm program PHLIP for total biovolume and mean thickness. At the inlet, almost all biofilms produced highest total biovolume and mean thickness; this was significant for P. putida (P < 0.05). In mixed culture biofilms at the inlet of the flow cell, biovolume contributed by L. monocytogenes cells, though not statistically significant, was higher than in monoculture L. monocytogenes biofilms (532% increase). In contrast, in mixed biofilms in the middle section and at the outlet, biovolume contributed by P. putida cells was much lower than in monoculture P. putida biofilms, with reductions of 183 % (middle) and 793% (outlet).