 Food @-@ borne pathogens that can survive on lettuce include Listeria monocytogenes , the causative agent of listeriosis , which multiplies in storage . However , despite high levels of bacteria being found on ready @-@ to @-@ eat lettuce products , a 2008 study found no incidences of food @-@ borne illness related to listeriosis , possibly due to the product 's short shelf life , indigenous microflora competing with the Listeria bacteria or inhibition of bacteria to cause listeriosis . 
