Effect of Modified Atmosphere Packaging on the Persistence and Expression of Virulence Factors of Escherichia coli O157:H7 on Shredded Iceberg Lettuce

What is it about?

Outbreaks of Escherichia coli O157:H7 infections have been associated with the consumption of bagged leafy green commodities. Fresh cut lettuce and spinach are placed under modified atmosphere packaging (MAP) to preserve quality attributes. However, it may be possible that these MAP conditions may enhance the virulence of this pathogens when stored at refrigeration or abusive temperatures. Our study investigated shredded lettuce inoculated with E. coli O157:H7 under three different MAP conditions at two temperatures, 4oC and 15oC, for up to 10 days. Our results showed that passive MAP conditions that allowed gaseous exchange promoted the largest reduction of E. coli O157 counts on shredded lettuce when stored at 4oC. At 15oC, these same conditions promoted the slowest growth of E. coli O157:H7. However these conditions at 15oC also promoted the highest expression of genetic virulence factors. Our results indicate that passive modified atmosphere conditions can affected the potential virulence of E. coli O157:H7 at abusive temperatures.

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