Biofilm formation Escherichia coli O157:H7 and Salmonella on spinach harvester blades

Authors: Patel, Jitu; Sharma, Manan; Millner, Patricia; Callaway, Todd

Submitted to: ARS Food Safety and Inspection Service Research Workshop
Publication Type: Abstract Only
Publication Acceptance Date: 2/18/2009
Publication Date: 2/18/2009
Citation: Patel, J.R., Sharma, M., Millner, P.D., Callaway, T.R. 2009. Biofilm formation Escherichia coli O157:H7 and Salmonella on spinach harvester blades. ARS Food Safety and Inspection Service Research Workshop. ARS-FSIS Workshop Poster #5.

Interpretive Summary:

Technical Abstract: Outbreaks associated with leafy greens have focused attention on the transfer of human pathogens to leafy greens during mechanical harvesting. Harvesting of baby spinach presents an opportunity for contaminated blades to transfer bacterial foodborne pathogens to recently harvested spinach. Biofilm forming ability of Escherichia coli O157:H7 and Salmonella on harvester blades immersed in spinach extract was studied. Individual cocktails of five Salmonella isolates and five nalidixic acid (NA)-resistant E. coli O157:H7 isolates were prepared. Twenty-five ml of spinach extract were inoculated with either E. coli O157:H7 or Salmonella cocktail at inoculum levels of 1 (low) and 4 (high) log CFU/ml. A sterilized spinach harvester blade (2 x 1”) was placed in inoculated extract and incubated at room (22 deg C) or dynamic temperature (30 deg C-day, 20 deg C-night) for up to 48 h. At specific times, 2 blades at each inoculum level were analyzed for E. coli O157:H7 and Salmonella populations. Populations in biofilms were determined by scraping the blade with a Teflon spatula, followed by spiral plating on SMAC containing 50 µg/ml NA (SMAC-NA) and XLT4 media for E. coli O157:H7 and Salmonella, respectively. When inoculated at 1 log CFU/ml, E. coli O157:H7 adherence to blades after 24 and 48 h incubation at dynamic temperature (6.09 and 6.37 log CFU/ml) was significantly higher than to those incubated at 22 deg C (4.84 and 5.68 log CFU/ml), respectively. E. coli O157:H7 populations recovered from blades after 24 and 48 h were similar (P>0.05) when inoculated at 4 log CFU/ml. The adherence of Salmonella to blade varied (P<0.05) with incubation temperature and time. Salmonella populations recovered from the blade when inoculated with 1 and 4 log CFU/ml (3.96 and 5.97 log CFU/ml) and stored at 22 deg C were significantly higher than those recovered at dynamic temperature (2.50 and 3.85 log CFU/ml), respectively. Biofilms were formed by E. coli O157:H7 and Salmonella on harvester blades under both static and dynamic temperatures. Effective cleaning to remove pathogens adhered to harvesting equipment would help prevent potential cross contamination with these pathogens during spinach harvest.