Shigella boydii 18: Characterization and biofilm formation

Shigella boydii 18 Chicago Department of Public Health (CDPH) was the cause of a foodborne outbreak involving bean salad. The S. boydii CDPH strain was found to be more acid tolerant than the S. boydii ATCC (American Type Culture Collection) type strain in tryptic soy broth acidified with glacial acetic acid. These microorganisms were found to survive in bean salad for the duration of the shelf life of the salad. Shigella boydii ATCC and CDPH grow on parsley and cilantro at room temperature and survive for over two weeks at refrigeration temperatures. Fit(TM) produce wash and water reduced S. boydii CDPH populations on inoculated parsley by 1.5 orders of magnitude, but did not completely eliminate this organism. Fit(TM) produce wash completely eliminated S. boydii planktonic cells.{09}Baking soda, lemon juice, salt, and white vinegar were not effective against S. boydii CDPH planktonic cells. Shigella boydii may be forming a biofilm on the surface of the parsley, which may explain why produce wash is effective against S. boydii planktonic cells, but ineffective against S. boydii on parsley. Scanning electron micrographs and environmental scanning electron micrographs reveal the presence of cells in biofilms on the surface of parsley and cilantro treated with produce wash. In order to examine the mechanism of S. boydii biofilm formation transformants containing the ompR and csg genes were generated. The S. boydii ATCC transformants produced copious amounts of curli as revealed in scanning electron micrographs. Fit(TM) produce wash and water yielded reductions in populations of S. boydii transformants on parsley similar to those observed with the wild type.