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United States Department of Agriculture

Agricultural Research Service

Research Project: MICROBIAL ECOLOGY AND SAFETY OF FRESH ON-FARM ORGANICALLY GROWN PRODUCE Title: Biofilm formation and bacteriophage inactivation of Escherichia coli O157:H7 on spinach harvester blades

Authors
item Patel, Jitu
item Sharma, Manan
item Millner, Patricia
item Callaway, Todd

Submitted to: Annual Meeting of the Institute of Food Technologists
Publication Type: Abstract Only
Publication Acceptance Date: February 10, 2009
Publication Date: June 6, 2009
Citation: Patel, J.R., Sharma, M., Millner, P.D., Callaway, T.R. 2009. Biofilm formation and bacteriophage inactivation of Escherichia coli O157:H7 on spinach harvester blades. IFT 2009 Annual Meeting Book of Abstracts. Paper No. 123-04. p. 148.

Technical Abstract: Outbreaks associated with leafy greens have focused attention on the transfer of human pathogens to leafy greens during harvest with commercial equipment. The role of this equipment should be investigated to develop mitigation strategies. Biofilm formation by Escherichia coli O157:H7 on a spinach harvester blade covered with spinach extract was studied. Bacteriophages specific for E. coli O157:H7 were evaluated to kill cells in these biofilms. A cocktail of five nalidixic acid (NA)-resistant E. coli O157:H7 isolates was transferred at two inoculum levels (1 and 4 log CFU/ml) in a 25-ml spinach extract. A piece of sterilized spinach harvester blade (2 x 1") was placed in a tube and incubated at room (22 deg C) or dynamic temperature (30 deg C-day, 20 deg C-night). At specific times, two blades at each inoculum level were analyzed for E. coli O157:H7 populations. Bacterial 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). Two blades were sprayed on each side with a cocktail of E. coli O157-specific bacteriophages before scraping the blade and subsequent plating on SMAC-NA. 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. Application of bacteriophages reduced E. coli O157:H7 by 2.5 and 4 log CFU/ml on blades after 10 and 120 min, respectively. Biofilms were formed on harvester blades under static and dynamic temperatures. The application of bacteriophages reduced E. coli O157:H7 on blades after 10 min, indicating its potential as an intervention step.

Last Modified: 10/21/2014